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Discussion Starter #1
'93 164L just started high idle behavior after starter replacement. We -did- disconnect the AFM hose in case we needed to go from the top to get at the top starter bolt, but that was unnecessary. Now, after reassembly, the car did the following:

1) on initial (short) test ride, son reported that on letting off throttle the engine would briefly speed up before settling to proper idle. This ride was only 5 minutes or so.

2) on 30 mile work commute, son reported that idle speed gradually rose, and foot-off-pedal idle at end of drive was 2800 RPM.

3) by end of ride home, "idle" speed was 3000 RPM.

I found that disconnecting the idle air control cable from the controller corrected the fast idle, but the car was not warm yet and would stall w/o IAC functioning. I don't know -exactly- what the faults in the system can be.

Question: Is the IAC control powered to 12V and controlled by grounding (like the radiator fan)? In such a case, an internal ground fault -could- result in actuating the controller and raising the idle speed. I -do- have spares on hand and plan to swap one in to check this.

Question: Is it more likely that the cable coming back from the IAC is chafed and that some ground fault is being caused there instead of internal to the IAC?

Thanks for any help. I may be totally off-base in my idea of how this functions. I just recently installed my 164 cardisc on my wife's Micro$oft computer. I normally use other OSs.

Michael
 

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Check that throttle body lever is going against idle stop and that min max switch is set correctly click on/off <1 degree.
 

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I Have the Same Problem, but Only When Cold

I also have a fast idle (approximately 2500-3000 RPM) on my 95Q (24V), but only when the engine (and ambient temperature) is cold. Have to check the IAC when I bring it out of storage. But then, it may be warm enough that the problem does not occur.
 

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Discussion Starter #4
And he hangs his head in shame....

One of the problems with getting old(er) is that you come to think you have made and can avoid the simple mistakes. Not so! Don't bet on it. My son and I had both inspected the IA and oil separator hose junctions where they come off from the AFM hose, and pronounced them intact. So I went out today in the not-so-cold but rather drizzly out of doors to address the high idle issue, bringing with me some tools and a spare IA valve ready to install it. But, reasoned I, maybe I am after all NOT perfect in my understanding, and there may yet remain some simple thing which may be done to restore yon engine to running order. Forsooth, and all that.

So to inspect the throttle plate as instructed by the esteemed and inimitable Alfisto Steve, I disconnect the AFM and remove the AFM hose from the... oh. The oil separator junction was just barely made up. Gee. That's funny. And that's the only place up here that I disconnected when I was preparing to replace the starter. Hmm.

Well, I -really- should look at the throttle plate while I'm here. OK. It's closed and just a bit of opening motion causes the switch to click. So the ECU is getting the throttle closed signal and the throttle is indeed closed. So rather than just swapping IA valves, even though the high idle went away when I pulled the IA power wires from the valve and I THOUGHT that meant the idle air valve was being held unnecessarily widely open by the ECU, I buttoned it all back up and gave it the acid test. She started immediately (appropiately gratifying, after starter replacement), bopped up to about 1k RPM and then settled sedately back to (ready?) the spec ~800 RPM.

OK. Fixed? Let's put away our tools and see if that coaxes misbehavior out of the little lady. No dice. Still has the proper idle speed. So we go for a 1/2 mile trip down to the corner and back. Looks great. All fixed.

So, I'm incapable of interpreting the signs. I found that a false air leak into the AFM hose -CAN- be overlooked by the ECU/lambda-sensor mixture test, and make a high idle with no Check Engine light. I think this means that the ECU has a minimum opening signal that it puts on the IA valve, and that removing this signal CAN result in a stalling engine. In hindsight, the stalling might have been a sign that the high idle was pulling enough air through the AFM to make it wake up the ECU and make it stuff some fuel into the car. But pulling the IA wire reduced the flow to the point that with less fuel programmed by the ECU, the mixture went too lean to run and the car would stall. But I didn't check for mixture, as I'd decided it _MUST_ be the IA circuit and the mixture _MUST_ be OK fast or slow.

So, I think I know the mechanism. I think I"m educated that false air does not necessarily make the Check Engine light come on with mixture warnings. And the car now runs after undoing a Bad Thing I did during maintenance. Acceptable end of story. Don't fall into these traps, yourselves.

Michael
 

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Been there on way to daughter's soccer practice with her driving and car dies. Running late we swap drivers and car restarts and being late we rush on to practice.

She runs onto field I open hood and inspect engine and find nothing wrong that I can see so I try to start car and it won't idle.

Call tow truck and after practice still waiting but they finally come and take us and car home on the hook.

After car safely backed into garage and I open hood and right away see oil seperator hose elbow is completely out of inlet tube.

My guess is was laying almost in place at soccer field but allowing false air and bouncing ride with tow truck popped it all the way out so then clear to see.

Only cost me $50 for tow to find problem.

I still have the "Still Plays with Cars" though faded, torn and tie dyed.

Murphy is always around with his Law.
 

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Just one more observation from me, though this might apply only to my 164s without lambda/cats:

The idle air valve is driven by a pulse waveform that both closes and opens it. If you unplug the idle air valve, the valve becomes part-open and idle speed goes to about 1000RPM - a brilliant piece of fail-safe design. Reconnecting the valve should cause the idle speed to drop slightly, not increase as you might expect.

I have often forgotten to tighten the large hose clamps on the corrugated pipe, and also forgotten to reconnect the throttle position switch. 3000RPM does sound mighty high though, like a sticking throttle cable?

Glad to hear it's fixed and you found it an entertaining experience.

-Alex
 
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