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Discussion Starter #1
Hi I have a 1991 bronco Eddie Bauer edition with the 5.8l with an automatic tranny and I’m having some issues with it while driving and while idling in the mornings...when I give it gas is jerks a little and won’t get out of its own way...and when I start it in the morning it will do the high idle then drop back down like normal but after that it revs up to about 2200 rpms then drop back down over and over again then it will stop and go into normal idle and if you tap the gas (while it’s still in park) it revs back up and stays at 2200 rpms for a minute or two.... this is my only vehicle and I need it to get to and from school and work so any help will be very much appreciated!
Also I have replaced the IAC,TPS,and the MAP sensor
Thanks!
 

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Discussion Starter #3
Have you pulled codes? Check for vacuum leaks - disconnected or broken plastic vacuum lines and intake gaskets. Check to see if your throttle linkage on top of your throttle body is sticking and not going all the way back to zero.
Have you pulled codes? Check for vacuum leaks - disconnected or broken plastic vacuum lines and intake gaskets. Check to see if your throttle linkage on top of your throttle body is sticking and not going all the way back to zero.
the check engine light comes on when I get to about 25 mph so I haven’t been able to pull codes because it only comes on in drive and my throttle linkage isn’t sticking and I have checked vacuum lines with starter fluid and they all seem good I’m thinking it could be my throttle body is there a way to test it? And if there is how would I go about doing that?
 

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The Tennessee Warden
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You can still pull codes even if you don’t have a code reader, and the codes will still be there in the memory even if the CEL isn’t lit. I would start there and check back with the results. Here’s a link to the procedure:


 

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How much does it cost to have an auto parts store pull codes because I don’t know how to use obd1 very well I’m only familiar with obd2 and what kind of code would it be for the throttle body
 

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The Tennessee Warden
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An auto parts store may pull codes for you for free, but I'm not sure if they will pull OBD1 codes or not. They might - call around. Otherwise, if you follow the procedure I linked in my last post, all you need is a paper clip to jump two plugs on the self test connector and a piece of paper and pencil. You follow the steps and then count flashes of the CEL. That will result in numbers that refer to the Ford OBD1 code list. You can list those numbers here and we can try and help you diagnose your issue.

If the linkage on the TB is sticking, that probably won't throw a code. It may need cleaning though - some throttle body cleaner (not carb cleaner) might help if the butterfly valves are gummed up. When it's high idling, see if you can push the throttle lever to lower the idle.

I have a video of my old 88 here with a sticky TB lever.
 

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Yo Djspeers3,
Call local non-chain auto parts stores for scanning your 91 for codes. Tge chain stores used to do it, but since non obd 2 vehicles are old...

Try a Self Test for Diagnostic Trouble Codes (DTC)s by my pal, BroncoJoe19
http://broncozone.com/topic/14269-code-reader/?pid=74587&mode=threaded
PCM stores the Self-Test program in permanent memory. When activated, Self-Test checks the EEC system by testing memory integrity and processing capability, and verifies that various sensors and actuators are connected and operating properly.
Inspect the air cleaner and inlet ducting. KCheck all engine vacuum hoses for damage, leaks, cracks, blockage, proper routing, etc. Check EEC system including the wiring harness for proper connections, bent or broken pins, corrosion, loose wires, proper routing, etc. Check the Powertrain Control Module (PCM), sensors and actuators for physical damage. TPS, ICM, DISTRIBUTOR, etc. Check the engine coolant for proper level and mixture. Check the transmission fluid & engine oil level and quality. Make all necessary repairs before continuing with SELF TEST.
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test. Run it around to heat the engine up and shift thru all gears including Reverse. Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual & release clutch. Then turn off engine, all accessories/lights (close driver's door) , etc.
Do KOEO test First. Post Code(s) here according to KOEO & KOER.
A helper can assist you by counting the codes. Some use their smart phones to record them.
BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS
Or ask local mom and dad parts stores if they will test it for you.
Or purchase a coder reader such as Equus 3145 Innova OBD I Code Reader for Ford EEC IV Engines at Walmart & most parts stores.
 

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Yo,
Some no code usual suspects by Ford;
Vacuum leak, see my leak diagnosis link in post #11


Air filter, is it relatively clean?
Air inlet atop radiator support to filter box and to throttle body; look for obstruction; damaged tubing, openings in tubing, loose fit at throttle body or if equipped, at MAF sensor.
Fuel quality; Oxidized fuel often turns darker over time and may even smell sour. You can check stored gasoline by pouring some into a clear glass container and comparing it side-by-side with known fresh gasoline. If your old sample looks noticeably darker than the fresh gas, you have strong evidence the gas has gone bad.
Electrical connectors; inspect for corrosion, etc at coil, firewall, ICM, distributor, PCM, etc. especially those with broken locking tabs.
 

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Discussion Starter #9
My air filter is brand new I think I found my problem it’s a vacuum line but I have no clue where it goes I’ll post a pic of it too it’s the darker yellow one
 

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Yo d,
150904

thermactor air-bypass (TAB) valve Pic in a 90 by SeattleFSB
on passenger side of engine
 

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Discussion Starter #12
Do u have a link to the specific vacuum line I need to purchase or can I just plug it for now?
 

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Yo D,
Plug it for now.
Sorry, I posted the wrong pic yesterday, poor vision.
Here is correctt color:
Yellow Vacuum Line goes from the TAD Solenoid (driver's side forward solenoid) to the TAD (Diverter) Valve located at the rear of the Intake Manifold on Crossover (aka "Y") tubing.
150963
 

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Discussion Starter #14
Do I plug the yellow line and the spot it’s supposed to be connected to or just the yellow line
 

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Ok thanks just wasn’t sure I’ll plug it and take it for a drive and I’ll let you know how it goes
 

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Discussion Starter #17
So I plugged the line and it has much better power but it still idles up and down when it’s cold so what could that be?
 

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Yo Dj,
Try unplugging the Idle Air Control (IAC)

Location pic by Steve
Testing..
"First let me say this little thing has many names. But they all talk about the same item under the hood. Here all the names I've had the torture of learning throughout the years:
•Idle Air Bypass •Idle Air Control •Idle Speed Control •Throttle Bypass Air •Idle Bypass •Inlet Air Controller
•Inlet Air Bypass •Intake Air Bypass •Intake Air Control.
This is really easy to test. First as with all problems you should gather the trouble-codes from the computer. Follow the codes for testing and repair. If you get a code that points to a problem with the IAB start the vehicle 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 IAB. If the engine begins to stubble or stalls the IAB is functional and does not need to be repaired. If the engine idle does not change you should remove the IAB for inspection.
The IAB 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 IAB to function properly. Remove the IAB and clean it. There are 2 halves to the IAB, 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 IAB needs to be replaced." By Ryan M.
...
This is by Nelbur; "I have spent some time this week trying to set up an air bypass around the IAC valve by cutting away some of the gasket between the IAC in and out air holes, rather than pay big bucks for Fords spacer kit. I cut away the center of the original IAC gasket from the outside of each hole to the outside of the other hole, giving about 1/2" gap for the air to pass through. I noticed an immediate improvement in the engines starting behavior, but it would still die occasionally.

For most of my trucks life it has been dying when it was started hot. It would rev up and then drop the idle so low it would die unless I would catch the idle with the accelerator. It would never die when cold as the IAC would keep the idle speed up, and it never died at stop lights. Now it's worst situation seems to be when it has been shut down for a half hour or so, and restarted. I wonder if the heat soak is fooling the ETC into thinking the engine is warmer than it really is.
I decided that more improvement could be had if I had a thicker gasket, because the original IAC gasket was very thin (0.018"). I had some 0.030" gasket material so I made my own with the same 1/2" cut out. This gave enough bypass to noticeably raise the idle speed and almost eliminate the dying. After maybe 50 starts in the last few days, it only died twice. After so many years of catching it with the accelerator it is darned hard to leave my foot off it. It is clear to me that by trial and error one can tune the air bypass without the need for the expensive Ford kit. I may combine the two gaskets for more bypass, but the idle is about as fast as I would want now, especially for driving in snow."

Nelbur mentioned this Ford kit in..Idle Air Control (IAC) Sludge; Poor Idle TSB 91-25-07 for 85-92 Bronco & F Series & many others; "...Hard cold starts, hesitation and stalls on initial start-up or during idle or decel may be caused by sludge in the throttle body and/or idle by-pass valve. Sludge deposits or oil film on the throttle body bore and plate or the idle air by-pass valve may cause one or more of the following conditions. Hard Cold Start, Stall On Initial Start-Up, Stall During Idle, Stall During Decel, Rough Idle, Rolling Idle, Hesitation During Acceleration. A new idle air by-pass service kit (F2PZ-9F939-A) is now available for service use to correct sludge contamination concerns of the throttle bore and plate only. It eliminates the need to clean the majority of past model throttle body applications. Cleaning is not required on sludge tolerant throttle body designs released for 1991 and newer model years..."
 
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