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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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Discussion Starter · #1 ·
I’m dealing with a very high idle when I shift back to park after driving any distance. I’m dealing with it about 90% of the time. My normal idle is around 750 and I have no tach but feels like 1400-1500 in Park. Occasionally, for some odd reason, it returns normally. Usually if I try to wait it out to come down, it will not. Once in a blue moon, it settles after an extended time in P.

I have:

Checked for vacuum leaks with carb cleaner on cold engine (none found)

Replaced IAC

TPS was recently replaced for another issue

New Throttle cable was recently installed and linkage appears to operate normally

Replace intake plenum gasket

Replaced valve cover gaskets

Inspected intake for damage (there is a hole in the snorkel tube before the filter, but nothing after the box)

I know there are some other posts on this topic. Anything specific about my case that jumps out?
 

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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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8 Posts
Discussion Starter · #2 · (Edited)
Follow up...

Forgot to mention, about 90% of the time the rig will accelerate to almost 25 mph without even touching the pedal when I put it in gear. It seems any time I turn off the truck with the rpm’s surging, it will have way too much initial power in gear when I turn it back on next. Even next day etc.

KOEO:nothing
CM: 34, 63
KOER: 34, 44

About a month ago I re-attached the crossover tube on the passenger side. It was hanging freely. Appeared the bolt had backed out. No sign of the original bolt and threads were intact. Tube snugged back up well.

Only other repair was replacing white vacuum tube for ac near the firewall. Transmission has a fresh re build and Tranny builder requested I solve the rpm issue and bring it back to fine tune shift points.
 

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code 63...
63
Throttle Position Sensor (TPS) signal too low TPS​

My first thought was vacuum leak... surging idle.
Then TPS, But I see you changed it out. (it might still be bad)
So I checked your codes..
63
Throttle Position Sensor (TPS) signal too low TPS​

That could be a bad ground. I didn't look it up, but significant grounds are at the upper radiator support, both left and right. Certainly grounds from the battery are important.
 

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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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8 Posts
Discussion Starter · #4 ·
Thanks. I will check the grounds. I did have to remove some when replacing valve cover gaskets
 

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Yo T,
As BroncoJoe19 advised on a vacuum leak.
166883

Gauge should show approximately 15" of vacuum.

DTC 34 - EGR voltage above closed limit
...in Key On Engine Off (KOEO) or Engine Running (KOER) Self-Tests; indicates that the EGR valve may not be fully seated in the closed position; or the EVP sensor voltage is greater than the closed limit voltage of 0.67 volt. Because of the preload on the installed EVP sensor, it is very difficult to determine whether the EGR valve is seated or the EVP sensor is in contact with the EGR valve stem.
•Faulty Vacuum system - See my Vacuum leak test in post #11 it It includes locations of components that use vacuum.
One way to do a quick check is to grab a vacuum gauge. Some parts stores will loan you a gauge with refundable deposit.
In general, the vacuum gauge should read between 15 and 22 in-Hg depending upon the engine, condition and the altitude at which the test is performed. SUBTRACT ONE INCH FROM THE SPECIFIED READING FOR EVERY 1,000 FEET OF ELEVATION ABOVE SEA LEVEL.
The reading should be quite steady. .
When engine is rapidly accelerated (dotted needle), needle will drop to a low (not to zero) reading. When throttle is suddenly released, the needle will snap back up to a higher than normal figure.

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.

•Damaged EVP sensor
•Corroded or dirty connector
•Damaged EGR valve
•Broken wire in harness
•Grounded harness
•Damaged Computer
Failed sensor, carbon between EGR pintle valve and seat holding the valve off its seat.
Remove the EGR valve and clean it with carbon remover and a brush if necessary

Prior to re-installing see if you can blow air through the flange side of the EGR by mouth.

EGR Valve Position (EVP) Sensor Testing @ Ford Fuel Injection » EGR Valve Position sensor (EVP)
by Ryan M

63 KOEO TPS circuit below minimum 0.6 volts.
CM TPS circuit has intermittently failed below minimum 0.6 volts.
Test @ Fuel Injection Technical Library » Throttle Position Sensor (TPS) by Ryan

DTC 44 (KOER); AIR system inoperative – Air Injection; "...I had a similar issue that turned out to be the vacuum line to the Thermactor Air Bypass Valve. No CEL, just a code; 1. First check that the two vacuum lines are connected to the Vacuum Reservoir (coffee can) and the resevoir is in good repair with no leaks on the bottom. Frequently the can leaks or the vacuum lines are accidentally knocked off. Check the vacuum hose to the bottom of the TAB (Bypass) Valve. Check the vacuum hose to the TAD ( Diverter) Valve. Check the vacuum hoses to the TAB/TAD Solenoids.
Then check your TAB/TAD Solenoids. These are common easy to miss problems. Once these are ruled out all that is left is: Thermactor Air Supply Hoses. One-way Check Valves. Main TAB/TAD Valves..."*
 

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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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8 Posts
Discussion Starter · #6 ·
Thanks. I will be borrowing a vacuum gauge and pump this weekend.

The first picture represents the vacuum system currently in my truck. The second picture is of the sticker under the hood. It doesn’t match the configuration actually on the truck. I believe PO had the engine rebuilt... Maybe they reconfigured vacuum system then? I’d like to confirm the routing to and from each component. All is pretty simple except which is TAB and which is TAD solenoid. How do I tell the two apart to confirm hose routing? Also, how do I function test those solenoids?

Floor plan Plan Technical drawing Diagram Drawing Text Font Architecture Drawing Electronics
 

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Yo T,

See Booba's vacuum hose replacement in an 89 F150 @ Replace Plastic Vacuum Hoses with Rubber - FSB Forums
It includes Seattle FSB's 90 vacuum hose replacement with silicone.


; "...Key off. Disconnect both AIRB/AIRD solenoid connectors and measure both solenoid resistances. Is each resistance between 51 and 181 ohms?..."
Source: by Jim

Thermactor Air Diverter Solenoid (TAD, AIRD, AM2); "...is controlled by the EEC-IV computer and provides vacuum to the Air Bypass/Air Control Valve. With vacuum present, air flows to the exhaust manifold. With no vacuum, air flows from the air pump to the catalyst..."
Source: by Ted F

The Dual Thermactor Air control Solenoid Valve assembly consists of two normally closed solenoid vacuum valves, the thermactor air bypass valve and the thermactor diverter valve (TAB and TAD). When de-energized both are vented, sourced by the intake manifold vacuum reservoir and controlled by an EEC system (Refer to Computerized Engine Controls for diagnostic procedures).
 

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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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8 Posts
Discussion Starter · #8 ·
Update... Surging issue is more intermittent as of late, but rpms seem to be going higher when it does occur. Also seems the rpm’s will stick/linger at times while driving after I take my foot off the pedal.

Also occasional “cough”/sputter at morning start up recently. It does not stall, but does hiccup initially.

I have also noticed in Park when the rpm’s are surging they will fluctuate as I cycle through functions on the ac system.

Last thing to report, probably unrelated, but I have significant clunk when dropping into reverse. Occasionally it does not clunk.

Would broken/stuck check valve in TAB or TAD valve produce surging engine RPM in park? That’s one thing I have not been able to test yet.
 

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Yo T,

Update... Surging issue is more intermittent as of late, but rpms seem to be going higher when it does occur. Also seems the rpm’s will stick/linger at times while driving after I take my foot off the pedal.
Vacuum Leak, borrow a vacuum gauge and do my test

Also occasional “cough”/sputter at morning start up recently. It does not stall, but does hiccup initially.
TPS

I have also noticed in Park when the rpm’s are surging they will fluctuate as I cycle through functions on the ac system.
Vacuum leak.

Last thing to report, probably unrelated, but I have significant clunk when dropping into reverse. Occasionally it does not clunk.
Could be dreiveshaft u joints

Would broken/stuck check valve in TAB or TAD valve produce surging engine RPM in park? That’s one thing I have not been able to test yet.
A broken check valve will cause a vacuum leak.
 

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1989 Custom, 5.8L. C6, Manual Tcase, Manual Hubs
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Discussion Starter · #10 ·
Thank you very much
 
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