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strange idling problem- need help now

yosh18981898

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I've got a 92 X sport. Lately it has had a problem idling when it is cold, When you start it up cold, the engine revs to about 2000 rpms then after about 20 seconds the rpm's quickly fall to about 400 then it sudders and dies. After you restart it about 4 times, it wont die anymore but still revs to 2000, falls to 500, shudders, revs to 2000, falls to 500, shudders......
In the last week it has started to continue having the problem once it is warmed up, I mean, every time I push the clutch in to shift the rpms quickly fall to 500 then rev to 1000 then back to 500 until I reengage the clutch. Everything seems to work fine once you put your foot on the gas. My 16 year old mechanic wantabe friend told me I might need a whole new computer for $800 bucks, but I find this hard to believe seeing as how the truck only has 84000 miles on it.

This is driving me crazy I want it fixed now! Can anyone help me?
 



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yosh18981898

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I cleaned the IAC and replaced the Idle Air Control Motor. This helped but the problem is definately still there. Any more Ideas?
 






fastcougar

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Pull the spark plugs and ensure that the plug gap is within range (.054 IIRC). This is the most likely culprit and very easy to fix. As long as you are in there getting your hands dirty, might as well replace them with new plugs.
 






yosh18981898

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I just replaced and gapped the plugs about 5000 miles ago. That can't be the problem. I'm pretty sure this a computer/electrical problem because the engine will run fine until some part makes this click noise then the rpm's fall, the engine shudders and sometimes dies and other times recovers.
 






88vert

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What about the TPS?
 






yosh18981898

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I just cleaned the Throttle Position Sensor. Didn't help. I'm beginning to think I might actually need a new ECM. Has anyone ever heard of a 1st generation ECM going out?
 






MrShorty

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It's rare, but not unheard of for the PCM to go out. Can you identify the part that "clicks" just before the engine performance goes south?
 






yosh18981898

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I'm almost positive it is the Idle air control motor, but that was the first part I replaced in my attempt to fix the problem. I just had another idea, it wouldn't be the fuel filter, would it? I mean what if the idle air control motor is functioning properly and is supposed to click when it lowers the engine idle speed to the correct 700 rmps, only when the engine is idling that slow, it can't suck enough fuel through the bad fuel filter, causing the stalling. Just a thought, does it make sense?
 






Nate1

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How is you AC system working? That click may be your compressor clutch engaging.
 






88vert

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Originally posted by nweibley
How is you AC system working? That click may be your compressor clutch engaging.
I was thinking the same thing.Try unplugging your a/c compressor then see if it still clicks:)
 






yosh18981898

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the A/C blows Ice Cold. I know what the A/C clutch sounds like. This click I'm talking about is a louder and sharper noise.
 






dogfriend

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Taking a wild stab at it.....


I think that it is almost certain that the problem is with the IAC. I know you replaced it, but the symptoms are exactly what you would get if it were working intermittently. I think that it is possible that you have a bad connection somewhere in the circuit that controls the IAC. The clicking noise that you hear is when the power is applied to it and it starts working again. Problem is that the signal sent by the PCM should be continuously on.

I think you need to verify 3 things:

1) IAC is electrically ok

2) Wiring between IAC and PCM is ok

3) PCM is sending a continuous signal to IAC. The signal from the PCM is a Pulse Width Modulated signal, but you should see a varying voltage on a digital voltmeter.

IAC = ISC in the page below
 

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dogfriend

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Also, check to make sure that the inside of the throttle body isn't all gunked up.
 






yosh18981898

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Thanks for the advice. I'll try the tests when I get the vehicle back from my friend who is replacing the power steering pump. (You know those 1st gen. PS pumps!!) I'll let you know what I find out.
 






blueox

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Dogfriend you always have such detailed answers......Thanks. It must take alot of time to do that.
 






dogfriend

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The info I posted came from this book. It is a very good reference especially for the 91 - 95 Explorers which use EEC-IV. Unfortunately, the author died so there won't be a follow up book for EEC-V.
 

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blueox

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Well whadda ya know I've seen a copy of that book before......it's downstairs.
 






yosh18981898

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I did the tests. I think I failed test number 3. I got zero volts with the engine running, ignition on but engine not running, and ignition and engine off. I made sure I had good connections on the probes so I am sure I failed this test. I guess this means that I've got a bad connection somewhere in the wiring. At least I know I don't need a new computer. Does anyone know where the VPWR wire goes from the Idle air control motor? Does it just go to the positive battery terminal? Where can I get a wiring diagram for a 92 Explorer?
 



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yosh18981898

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I forgot to say that I checked the signal coming from the computer, it looks to be working properly. Also, my throttle body is probably cleaner than when it was new, I sprayed about a half a can of carb and choke cleaner in there in an attempt to fix the problem.
 






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