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Discussion Starter · #1 ·
Is there a good way to clean the TPS (does it open up)? Or do I just blast it with contact cleaner and hope for the best?
 

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Contact cleaner would be my guess. Ifyou plan on making it to North Bend maybe we can set up a meet.
 

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Before you start spending time on the TPS, are you sure there's anything wrong with it? This is copied from Fred Lane's advice;

If the ECU doesn't realise the throttle is closed, it won't start controlling the idle. So correct setting of the throttle position sensor, either switches (Bosch LH2.2. and 2.4) or potentiometer (Lucas and Bosch 2.4.2) is essential. The instructions for the Lucas system are:-
a) Connect a voltmeter between terminal 2 and 3 on the throttle pot.
b) Slacken the screws securing the throttle pot to the inlet manifold.
c) Turn on the Ignition, and rotate the throttle pot so that the reading on the voltmeter is maximum of 400 mV,or 0,4 Volts. If this is not possible, you might need to enlarge the holes (for screws) on the T. pot.
d) Retighten the securing screws.
Note that the voltmeter should read between 4.2 and 4.9 volt at full throttle.

The Bosch settings for idle switches (LH2.2 and 2.4) are in the Bentley manual. The idle switch (pins 1&2) should open as the throttle just comes off idle. The full throttle switch (pins 2&3) should close at 72 degrees of opening. Bentley notes that the switch assembly, if wrongly adjusted, can hold the throttle open. For Bosch LH 2.4.2, the potentiometer, pins 2&3, should give 0.25volts at idle and 4.0volts at full throttle. The ECU also checks road speed before running the AIC, there's a sensor in the speedometer. On Lucas jack up one front wheel and spin it, you can then measure a signal at pin 6 of the ECU that varies between 0.5 and 5.0volts. On automatic cars the ECU also detects when you move to D or R. If you have air con the Bosch system detects whether it's on."
 

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Discussion Starter · #4 ·
This is a Bosch LH 2.4.2 system (should have mentioned that).
I'm going to restart my troubleshooting process this weekend.
The car is running rich, has a hard time idling without driver intervention and stutters randomly. I have redone all the grounds, I replaced the Lambda sensor last fall but I'll bet it's sooted up (it is producing voltage). I'm 90% sure there are no vacuum leaks, but I haven't checked the brake booster (pedal is hard, but works) - can I isolate that for vacuum testing?
 

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LH2.4.2 and LH2.4 ECUs should be able to give you some error codes to assist you in the diagnosis.

If the ECU and the Check Engine light are fully functional, AND if the car is running rich, I expect the ECU to have either the CE lamp on or at least some logged (stored) error codes painting fuel mixture troubles.

The TPS as a rule only dictates fuel discharge at wide open.........."full enrichment mode".

For fuel mixture irrregularities, I would be more suspicious of the AMM or NTC probe.....Exhaust O2 (lambda) probe is primariliy reporting the issue after the fact....not the cause.

Good Luck
 

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This is a Bosch LH 2.4.2 system (should have mentioned that).
I'm going to restart my troubleshooting process this weekend.
The car is running rich, has a hard time idling without driver intervention and stutters randomly. I have redone all the grounds, I replaced the Lambda sensor last fall but I'll bet it's sooted up (it is producing voltage). I'm 90% sure there are no vacuum leaks, but I haven't checked the brake booster (pedal is hard, but works) - can I isolate that for vacuum testing?
Yes you can conduct 3 tests to determine if your brake booster is faulty. If it fails any of these tests it is likely to be leaking vacuum.

air tightness test - engine off - pump brake pedal several times, with each subsequent pump pedal travel should decrease, if it doesn't brake booster is faulty

air tightness test under load - engine on - depress brake pedal firmly, hold brake pedal down and switch engine off - pedal should not rise or fall for 30 seconds (maintain pressure) if it does brake booster is faulty.

booster function test - engine off - depress pedal firmly and hold in, start engine, pedal should sink substantially - if it doesn't brake booster is faulty.

A simple test is to apply vacuum to the line of the brake booster, if it pulls air through it's faulty. You can buy reconditioned boosters for around $150. I have one, it's amazing how light the pedal is, barely needs any foot pressure to produce braking effort.
 

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If the car is LH2.4.2 MY91 on, there's a fair chance the car will have ABS.........no vacuum booster.
All hydraulic.
 

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........now what?
Well this,
........but I haven't checked the brake booster (pedal is hard, but works) - can I isolate that for vacuum testing?.......
you don't need to consider.
Check the error codes from the ECU and it may start to tell some hints as to what is wrong.
 

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This is a Bosch LH 2.4.2 system (should have mentioned that).
I'm going to restart my troubleshooting process this weekend.
The car is running rich, has a hard time idling without driver intervention and stutters randomly. I have redone all the grounds, I replaced the Lambda sensor last fall but I'll bet it's sooted up (it is producing voltage). I'm 90% sure there are no vacuum leaks, but I haven't checked the brake booster (pedal is hard, but works) - can I isolate that for vacuum testing?
Time for stupid question...when was the last time you checked your air filter. Sometimes we forget the simple things, and my 93 did not pass smog until the air filter was changed. If it is clogged with pollen, or bypass oil, it will lean out the airflow and cause a rich condition. Vacuum to the ABS does not exist. I would also look for hardened grommets in the intake manifold and the valve cover to cause vacuum leaks. All the elbows and T's should be GENTLY flexed to check for cracks/cracking.
 

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Discussion Starter · #12 · (Edited)
TPS tested OK
AMM tested OK
Cleaned TB, AMM
Very recent air filter
New VC grommet
Still looking for a weakness...
After doing the above (and clearing codes), now runs fine :-/
 

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Discussion Starter · #13 ·
Mysterious CEL codes

Well, that little interlude is over - got the same codes today; cleared them and got them again right away.
Is it time to suspect the ECU? I'm dreading that.
 

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Well, that little interlude is over - got the same codes today; cleared them and got them again right away.
Is it time to suspect the ECU? I'm dreading that.
Uh, little thing about Check engine lights and codes. It may take up to 30 minutes of driving to totally clear them out of the system. An O2 sensor change took 15 min of driving to clear on my stepson's 88.
 

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Uh, little thing about Check engine lights and codes. It may take up to 30 minutes of driving to totally clear them out of the system. An O2 sensor change took 15 min of driving to clear on my stepson's 88.

To clear codes once you have read them turn your jumper switch back on and wait for 3 short flashes then turn the switch to the off position.
 
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