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Discussion Starter #1
So i been driving my baby around, fixed a lose wire for the 02 sensor, runs fine
but then i noticed that my idle was slowly getting up and now on a stop light it idles at 1200 RPM

1. im going to check all my vacuum lines to make sure nothing is bad
2. i replaced spark plugs and wires
3. tps is new
4. the previous owner took the thermostat out to make it run cooler, could it be that?
5. engine surges sometimes

could it be the EGR?
i know its a common guestion, so sorry
 

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You're on the right track IMHO. Doubtful it's the EGR as idle speed should fall off with the introduction of exhaust gases (inert gas, kind of) at idle--which shouldn't happen as the PCM won't open the EGR vacuum solenoid until engine speeds are well above idle. I'd revert back to OEM temp thermostat. If a lower temp thermostat was installed because of engine getting hot in warm temperatures, lower temp thermostat won't buy you much as the opening is still the same, it's not going to give you more flow. My Bronco is sensitive to minimum airflow adjustment. To check that, remove the connector to the idle speed controller and see what happens. Engine should slowly die or barely run. As always, check for vacuum leaks, vacuum hose integrity, etc.

Dave
1987 Bronco Custom
4.9L
Mostly stock
 

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Many think a thermostat removed can possibly make the engine run cooler, I am not so sure.

I cant see any good from coming from leaving thermostat out, and I will tell you why:
I have designed numerous heat exchangers (radiators) and a fluid needs a bit of TIME to cool off and transfer heat thru the radiator and out to the atmosphere
Often times I will need to de-rate the pump to a lower GPM so the fluid has enough dwell time in the heat exchanger
When the fluid rips right thru there (without the Tstat restriction) it does not spend enough time transfering heat, and goes back into the engine actually hotter

I cant see any good coming from leaving thermostat out
If you had a flaky connection at the 02 sensor I would think your CEL would come on
What year and engine is your bronco?
There is a throttle dashpot that is famous for getting dirty on my '96 not sure if yours has one....it has a 3 letter acronym TPX, TPsomething
 

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Discussion Starter #5
Many think a thermostat removed can possibly make the engine run cooler, I am not so sure.

I cant see any good from coming from leaving thermostat out, and I will tell you why:
I have designed numerous heat exchangers (radiators) and a fluid needs a bit of TIME to cool off and transfer heat thru the radiator and out to the atmosphere
Often times I will need to de-rate the pump to a lower GPM so the fluid has enough dwell time in the heat exchanger
When the fluid rips right thru there (without the Tstat restriction) it does not spend enough time transfering heat, and goes back into the engine actually hotter

I cant see any good coming from leaving thermostat out
If you had a flaky connection at the 02 sensor I would think your CEL would come on
What year and engine is your bronco?
There is a throttle dashpot that is famous for getting dirty on my '96 not sure if yours has one....it has a 3 letter acronym TPX, TPsomething
yeah im going to put a new thermostat in when i can, also its a 92 5.0 L

the person just took the guts out of the thermostat and put in normally but doesnt have any of the control things to make it open

a few months ago i changed the TPS and at the same time i cleaned the IAC, the owner recently changed it, i have the old one he changed just in case
 

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Discussion Starter #6
You're on the right track IMHO. Doubtful it's the EGR as idle speed should fall off with the introduction of exhaust gases (inert gas, kind of) at idle--which shouldn't happen as the PCM won't open the EGR vacuum solenoid until engine speeds are well above idle. I'd revert back to OEM temp thermostat. If a lower temp thermostat was installed because of engine getting hot in warm temperatures, lower temp thermostat won't buy you much as the opening is still the same, it's not going to give you more flow. My Bronco is sensitive to minimum airflow adjustment. To check that, remove the connector to the idle speed controller and see what happens. Engine should slowly die or barely run. As always, check for vacuum leaks, vacuum hose integrity, etc.

Dave
1987 Bronco Custom
4.9L
Mostly stock
ok ill check the IAC
if the IAC checks out and no vacum leaks, what would be next?

and yeah im going to put a new thermostat in soon
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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Dirty IAC, vacuum lines would be my first thoughts. A friend that I drag race with owned a shop from 1975-2005 when he retired. He saw these trucks from the time they got their first oil change from new, right thru them being maintained as a 30 year old rigs. I had idle issues on mine & was over there one day & he made said pop the hood & he went right to the manifold vacuum tee where all the lines come from & pulled the vacuum lines off, 1 at a time and plugged the metal barb with his finger, so there was no vacuum leak. He pulled one & blocked it & the idle went right down and idled perfectly. It was the line that went to my cruise control. I put a vacuum cap on it & it was fine.

Good test method if you ask me.

I had a vacuum leak in the cruise control module, caused by it being rusted thru. I got a new module, & have the vacuum lines hookd back up with no issues.
 

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Discussion Starter #8
Dirty IAC, vacuum lines would be my first thoughts. A friend that I drag race with owned a shop from 1975-2005 when he retired. He saw these trucks from the time they got their first oil change from new, right thru them being maintained as a 30 year old rigs. I had idle issues on mine & was over there one day & he made said pop the hood & he went right to the manifold vacuum tee where all the lines come from & pulled the vacuum lines off, 1 at a time and plugged the metal barb with his finger, so there was no vacuum leak. He pulled one & blocked it & the idle went right down and idled perfectly. It was the line that went to my cruise control. I put a vacuum cap on it & it was fine.

Good test method if you ask me.

I had a vacuum leak in the cruise control module, caused by it being rusted thru. I got a new module, & have the vacuum lines hookd back up with no issues.
ill check it out! thanks !!
 

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1986 Eddie Bauer 5.0EFI AOD Full length headers Y pipe into single 3" Magnaflow 3" factory exit
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Its always good to listen to the old timers! They know a lot! Obviously your map sensor can't be pulled, or it dies (ask me how I know) Lol

absolutely put a thermostat in there, as others have said, heat transfer need time for the coolant to soak in the heat the engine, just as I needs time in the radiator to release the heat into the atmosphere.
 

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Discussion Starter #10
Its always good to listen to the old timers! They know a lot! Obviously your map sensor can't be pulled, or it dies (ask me how I know) Lol
HAHAHA good to know
 

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Yo FOX,
See my Vacuum leak test in post #11 @ Help with dtc codes and idle
When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.


High idle with no applicable codes is usually caused by a vacuum leak,

Other perpetrators are:
Intake manifold leak.
Sticking throttle linkages or throttle body plate is stuck - we had this occur recently! Sprayed throttle body cleaner on linkage atop throttle body and then light coat of WD 40 on linkage. Don't try to lubricate the cable internally.

Throttle Body top view pic in an 88 5.0 by jem270

Speed Control chain is binding, if equipped
Air intake tube is damaged
Throttle body return spring is loose
Throttle body is loose
Idle Air Control Valve (IAC)

"Start the Bronco and bring the engine up to operating temperature. Allow the engine to idle without any driver input to the throttle or pedal. Go under the hood, and disconnect the electrical connector to the
Idle Air Control Valve (IAC). If the engine begins to stubble or stalls the IAC is functional and does not need to be repaired. If the engine idle does not change you should remove the IAC for inspection.

The IAC can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAC to function properly. Remove the IAC and clean it. There are 2 halves to the IAC, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAC needs to be replaced." by Ryan M

How to Clean and Test your IAC by Seattle FSB @ How to Clean and Test your IAC

TPS Overview & Testing by Seattle FSB @ TPS Overview & Testing by Seattle FSB @ Bronco Forum - Full Size Ford Bronco Forum
¤
Mikey350 wrote, "Does your throttle body have a yellow warning sticker that says not to clean the throttle bores?
Try this: Take off the air intake hoses so you can access the throttle bores. Start the engine and place a piece of stiff cardboard over the throttle bores. That should NOT change a correctly configured engine, as the idle air is only from the opening of the IAC, and nothing through the throttle bores.
If that make a difference, then the throttle plates are slightly open due to the removal of the Teflon coating, or the linkage/return spring/throttle stop is screwed up.
If the engine still runs too fast with the throttle opening blocked, try taking off the IAC and blocking those openings.
What you have done is (supposedly) removed all the "normal" air intakes, and if the engine still runs, you have a vacuum leak.
You could then try leaving the air intakes (throttle and IAC) blocked and cap off the vacuum lines coming off the vacuum tree. (except the MAP line) If one of those makes a difference, investigate the leak.
Check the vacuum line from the vapor canister (on the left side of the throttle, when facing the throttle assembly) (cap it, on the outside chance that the solenoid has failed open) (if equipped)
Pull the EGR connection to the intake and plug or cover it. (if you have wide duct tape, use that to cover the hole)
If it still is running with the throttle blocked and the IAC and the lines from the vacuum tree capped, then you have a manifold or PCV line leaking. Plug the PCV line to the intake, then the vacuum line to the brake booster (if it has it's own fitting on the manifold)

Something is causing that high idle, and 95% of the time it is a vacuum leak
Good Luck
 

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Discussion Starter #12
Yo FOX,
See my Vacuum leak test in post #11 @ Help with dtc codes and idle
When vacuum leaks are indicated, search out and correct the condition. Excess air leaking into the system will upset the fuel mixture and cause conditions such as rough idle, missing on acceleration, or burned valves. If the leak exists in an accessory unit, such as the power brake, the unit will not function correctly. Or Air Conditioning when in MAX mode may switch to Defrost.


High idle with no applicable codes is usually caused by a vacuum leak,

Other perpetrators are:
Intake manifold leak.
Sticking throttle linkages or throttle body plate is stuck - we had this occur recently! Sprayed throttle body cleaner on linkage atop throttle body and then light coat of WD 40 on linkage. Don't try to lubricate the cable internally.

Throttle Body top view pic in an 88 5.0 by jem270

Speed Control chain is binding, if equipped
Air intake tube is damaged
Throttle body return spring is loose
Throttle body is loose
Idle Air Control Valve (IAC)

"Start the Bronco and bring the engine up to operating temperature. Allow the engine to idle without any driver input to the throttle or pedal. Go under the hood, and disconnect the electrical connector to the
Idle Air Control Valve (IAC). If the engine begins to stubble or stalls the IAC is functional and does not need to be repaired. If the engine idle does not change you should remove the IAC for inspection.

The IAC can pass and still need repair, or it can fail and not need replacing. The plunger and internal spring can get clogged with dirt and oil. This will slow down the air flow and not allow the IAC to function properly. Remove the IAC and clean it. There are 2 halves to the IAC, and you can not buy just one half, but you can take it apart to clean it. But if the internal solenoid is faulty the IAC needs to be replaced." by Ryan M

How to Clean and Test your IAC by Seattle FSB @ How to Clean and Test your IAC

TPS Overview & Testing by Seattle FSB @ TPS Overview & Testing by Seattle FSB @ Bronco Forum - Full Size Ford Bronco Forum
¤
Mikey350 wrote, "Does your throttle body have a yellow warning sticker that says not to clean the throttle bores?
Try this: Take off the air intake hoses so you can access the throttle bores. Start the engine and place a piece of stiff cardboard over the throttle bores. That should NOT change a correctly configured engine, as the idle air is only from the opening of the IAC, and nothing through the throttle bores.
If that make a difference, then the throttle plates are slightly open due to the removal of the Teflon coating, or the linkage/return spring/throttle stop is screwed up.
If the engine still runs too fast with the throttle opening blocked, try taking off the IAC and blocking those openings.
What you have done is (supposedly) removed all the "normal" air intakes, and if the engine still runs, you have a vacuum leak.
You could then try leaving the air intakes (throttle and IAC) blocked and cap off the vacuum lines coming off the vacuum tree. (except the MAP line) If one of those makes a difference, investigate the leak.
Check the vacuum line from the vapor canister (on the left side of the throttle, when facing the throttle assembly) (cap it, on the outside chance that the solenoid has failed open) (if equipped)
Pull the EGR connection to the intake and plug or cover it. (if you have wide duct tape, use that to cover the hole)
If it still is running with the throttle blocked and the IAC and the lines from the vacuum tree capped, then you have a manifold or PCV line leaking. Plug the PCV line to the intake, then the vacuum line to the brake booster (if it has it's own fitting on the manifold)

Something is causing that high idle, and 95% of the time it is a vacuum leak
Good Luck
Thanks again miesk5!!
i checked and its 90% sure its the throttle getting stuck since i had to push back the throttle back to make it idle.

checked vacum and took each one off and nothing changed the idle if i stopped it with the finger or plugged it in to the hose

Also i unplugged the IAC and the engine stalled/died so im sure thats working good
 
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Thanks again miesk5!!
i checked and its 90% sure its the throttle getting stuck since i had to push back the throttle back to make it idle.

checked vacum and took each one off and nothing changed the idle if i stopped it with the finger or plugged it in to the hose

Also i unplugged the IAC and the engine stalled/died so im sure thats working good
Yo,
In 2018, we had a sticking throttle linkage in our 96.
Our throttle lever atop throttle body stuck.
Cleaned it with WD 40; but don't try to lube the cable as per Ford.

"...Throttle plates in the throttle body not returning to the proper closed position...
Refer to the following procedure for service details. Visually inspect the throttle body and linkage for: * Binding or sticking throttle linkage. * Tight speed control linkage or cable. * Vacuum line interference. * Electrical harness interference. NOTE: AFTERMARKET GOVERNORS, THROTTLE LINKAGE AND CABLES ASSOCIATED WITH POWER TAKE-OFF UNITS, MAY ALSO INTERFERE WITH PROPER THROTTLE RETURN. SERVICE AS NECESSARY..."
Source: by Ford motorcraftservice.com

from 1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual

High Engine Idle Speed
Cable ball socket extends beyond the throttle lever ball stud - REFER to the throttle body diagnosis procedure in the appropriate section of the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII

foot pedal operation - ADJUST carpet, mat or wiring as required. CHECK the foot pedal assembly for free operation - my gas pedal popped off & it went to WOT when I wore snow pac boots once... it was a helluva ride/thrill!

Worn or damaged cable - GO to Pinpoint Test B.
B1 CHECK CABLE BINDING IN HOUSING
Disconnect the cable end from ball stud at throttle body.
Make sure the disconnected end of the cable does not come in contact with any of the surrounding parts.
From inside the vehicle, pull the wire through its entire travel.
Does it feel rough, sticky or restricted?
Yes - REPLACE as required. USE appropriate part with base No. 9A758. (VERIFY PN w/dealer, this if for a 96, but should be da same)

=
Installation

Follow removal procedures in reverse order.

Some new accelerator cables come with a plastic core protector over the end that goes through the instrument panel. Do not remove core protector until accelerator cable has been installed in instrument panel. Refer to the appropriate illustration for accelerator cable-to-instrument panel holding screw tightening specifications.

Fully seat accelerator cable grommets into slotted hole in accelerator pedal and shaft and dash reinforcement hole.


No - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required. GO to B2.

B2 CHECK CABLE RETURN
Let go of the wire after pulling on it.
Does the wire stick or hesitate to return to its original position?
YES - REPLACE as required. USE appropriate part with base No. 9A758.

NO - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required. GO to B3.

B3 CHECK RETURN SPRING
Compress the spring at the throttle body end of the cable.
Observe the cable as it returns to the original position.
Does the spring stick or fail to return to the original position at a rapid rate?
Yes - REPLACE as required. USE appropriate part with base No. 9A758

NO - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required.
 

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Discussion Starter #14
Yo,
In 2018, we had a sticking throttle linkage in our 96.
Our throttle lever atop throttle body stuck.
Cleaned it with WD 40; but don't try to lube the cable as per Ford.

"...Throttle plates in the throttle body not returning to the proper closed position...
Refer to the following procedure for service details. Visually inspect the throttle body and linkage for: * Binding or sticking throttle linkage. * Tight speed control linkage or cable. * Vacuum line interference. * Electrical harness interference. NOTE: AFTERMARKET GOVERNORS, THROTTLE LINKAGE AND CABLES ASSOCIATED WITH POWER TAKE-OFF UNITS, MAY ALSO INTERFERE WITH PROPER THROTTLE RETURN. SERVICE AS NECESSARY..."
Source: by Ford motorcraftservice.com

from 1996 F-150, F-250, F-350, F-Super Duty and Bronco Workshop Manual

High Engine Idle Speed
Cable ball socket extends beyond the throttle lever ball stud - REFER to the throttle body diagnosis procedure in the appropriate section of the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII

foot pedal operation - ADJUST carpet, mat or wiring as required. CHECK the foot pedal assembly for free operation - my gas pedal popped off & it went to WOT when I wore snow pac boots once... it was a helluva ride/thrill!

Worn or damaged cable - GO to Pinpoint Test B.
B1 CHECK CABLE BINDING IN HOUSING
Disconnect the cable end from ball stud at throttle body.
Make sure the disconnected end of the cable does not come in contact with any of the surrounding parts.
From inside the vehicle, pull the wire through its entire travel.
Does it feel rough, sticky or restricted?
Yes - REPLACE as required. USE appropriate part with base No. 9A758. (VERIFY PN w/dealer, this if for a 96, but should be da same)

=
Installation

Follow removal procedures in reverse order.

Some new accelerator cables come with a plastic core protector over the end that goes through the instrument panel. Do not remove core protector until accelerator cable has been installed in instrument panel. Refer to the appropriate illustration for accelerator cable-to-instrument panel holding screw tightening specifications.

Fully seat accelerator cable grommets into slotted hole in accelerator pedal and shaft and dash reinforcement hole.


No - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required. GO to B2.

B2 CHECK CABLE RETURN
Let go of the wire after pulling on it.
Does the wire stick or hesitate to return to its original position?
YES - REPLACE as required. USE appropriate part with base No. 9A758.

NO - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required. GO to B3.

B3 CHECK RETURN SPRING
Compress the spring at the throttle body end of the cable.
Observe the cable as it returns to the original position.
Does the spring stick or fail to return to the original position at a rapid rate?
Yes - REPLACE as required. USE appropriate part with base No. 9A758

NO - Cable is functioning properly. REFER to the throttle body diagnosis procedures in the appropriate section in the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII or ADJUST carpet as required.
( Worn or damaged cable - GO to Pinpoint Test B.
B1 CHECK CABLE BINDING IN HOUSING
Disconnect the cable end from ball stud at throttle body.
Make sure the disconnected end of the cable does not come in contact with any of the surrounding parts.
From inside the vehicle, pull the wire through its entire travel.
Does it feel rough, sticky or restricted?
Yes - REPLACE as required. USE appropriate part with base No. 9A758. (VERIFY PN w/dealer, this if for a 96, but should be da same) )

This is the problem im having, the small ball join with spring and everything, is pretty well......... used, kinda bendy and not returning all the way

also the throttle body spring might have to change it, whats the part number for that? or do i have to get a whole new assembly ?
 

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( Worn or damaged cable - GO to Pinpoint Test B.
B1 CHECK CABLE BINDING IN HOUSING
Disconnect the cable end from ball stud at throttle body.
Make sure the disconnected end of the cable does not come in contact with any of the surrounding parts.
From inside the vehicle, pull the wire through its entire travel.
Does it feel rough, sticky or restricted?
Yes - REPLACE as required. USE appropriate part with base No. 9A758. (VERIFY PN w/dealer, this if for a 96, but should be da same) )

This is the problem im having, the small ball join with spring and everything, is pretty well......... used, kinda bendy and not returning all the way

also the throttle body spring might have to change it, whats the part number for that? or do i have to get a whole new assembly ?
Yo Fox,
I haven't found a part number.

EntireThrottle Cable with its Spring in 92-96 BR PU @ Throttle Cable, 8 Cyl. 302,351W 92-97 BR PU-Broncograveyard.com
Item Number: 30792C
Unit Price: $36.00

Or take a chance on a yard queens cable.
For a YARD SEARCH on-line, I use;
https://www.hollanderparts.com
A yard that uses Hollander Interchange can search other yards and have it shipped.
 

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Discussion Starter #16
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Hopefully that cable fixes your problem if not, what brand tps did you buy. I went through 3 from Oreillys, all lasted about a month, before I ended up buying a motorcraft tps. When I installed them the bronco would run and idle great then the idle rpms would gradually creep up and up until I couldn't stand it and when I checked my voltage the tps would be out of range and I'd have to replace it again. Its been about a year since I put the motorcraft one on and I haven't had a problem since.
 

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Discussion Starter #18
Hopefully that cable fixes your problem if not, what brand tps did you buy. I went through 3 from Oreillys, all lasted about a month, before I ended up buying a motorcraft tps. When I installed them the bronco would run and idle great then the idle rpms would gradually creep up and up until I couldn't stand it and when I checked my voltage the tps would be out of range and I'd have to replace it again. Its been about a year since I put the motorcraft one on and I haven't had a problem since.
hhhmmmm i see, its a duralast one from autozone, i think i might have to check that, ill look into how much a motor craft is on rock auto
 

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Discussion Starter #19
Yo Fox,
I haven't found a part number.

EntireThrottle Cable with its Spring in 92-96 BR PU @ Throttle Cable, 8 Cyl. 302,351W 92-97 BR PU-Broncograveyard.com
Item Number: 30792C
Unit Price: $36.00

Or take a chance on a yard queens cable.
For a YARD SEARCH on-line, I use;
https://www.hollanderparts.com
A yard that uses Hollander Interchange can search other yards and have it shipped.
Also i noticed the TAB connector broken and not staying in place, whats the name for it so i can replace it? and maybe replace the relays as well

172914
 

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