No Initial High Idle

[ltmark]

Iv'e got an '85 that had some rough idle problems and various other minor problems. All are fixed except upon initial start-up, it immediately drops down to 600 RPM's and almost dies if I don't give it gas.

It has a new IAC, which I set according to the proper procedures...a new TPS which is at .54 volts and the MAS voltage is correct.

Anyone have an idea of the most likely problem? The 02 sensor is NOT new and I don't know if it has ever been changed...could that be the problem?

I get no codes and once warm, it runs fine and idles fine, with some very minor searching, ie. within 5 RPM's or so

 

[c4c5specialist]

HI there,
It sounds like the idle air control may not be reacting correctly.
The o2 sensor will not have any bearing on this idle condition, unless it is totally hot and has been running for a while.
Allthebest, c4c5

 

[ltmark]

Thanks.....I've done the procedure for adjusting the IAC several times, BUT, I have not been able to actually DRIVE the vehicle on the road at 45 MPH to enable the ECM to "learn" the new settings, (per the procedure) because it's not currently registered!. After my wife retired, it has been in the garage for a year. This is why I've had to go through everything, getting it ready for a "smog" test. It's just a 'bout ready, but still needs a new rear "y" pipe and mufflers, in addition to new paint. I have it all stripped and ready for the painter.

But, back to the main topic, would not actually driving it after the adjustments be the cause of the IAC proplem, if that's what it is?

 

[ltmark]

Just had a thought on my problem. Several years ago, I had a bad Park/Neutral switch and I "by-passed" the switch. Ready my shop manual, it says that it uses this P/N signal to control the Idle and EGR control. Maybe this is my problem!

 

[WhalePirot]

I believe the '85 has an extra injector for cold starts, while later versions use the ECM to add fuel through the 8 injectors.

I wonder if your 'cold' injector is not working properly?

 

[redc4corvette]

IAC set should be jump A_B with a wire or paper clip ,ENGINE STONE COLD ONLY!!! turn key on and disconect IAC plug .Without starting engine WAIT 90 SECONDS,remove the jumper wire and start engine.

Keep engine running and set idle at 400 rpm std trans and 450 auto .
Mantain engine running until it reaches operating temp.
Reconect AIC wire and then set tps to .54 volts.
whenever you disconect the IAC the tps voltage will have to be reset each time.
After all set run engine for at least 10 minutes .
In the am turn key and engine should start right up or repete process.
Yes you do have a 9th injector and the sensor for that is at the front of the engine.The injector is located on the drivers side center top of engine with the other injectors.

 

[SSTibet]

As far as idle air control valve has two sets of functions. (1) Idle air intake to the manifold when the engine is cold (open loop condition), and (b) idle air intake when operating in closed loop (following engine warm up). As far as I know engine rpm in open loop condition is a factory preset and can not be adjusted (or should not be tampered with).

 

[ltmark]

Thanks very much...this is a litle different from what I've been doing, primarily I wasn't doing it stone cold. Plus, I wasn't removing the jumper wire before starting after the 90 seconds. I'll try it in a little while and see what happens.

I appreciate the response!

 

[SSTibet]

Let me say it in other words. There are two modes the IAC valve operates. (1) Minimum idle speed - I am guessing that this is the amount of air that passes through the valve regardless of the conditions upon a cold start. This is a factory setting and should not be tampered with. (2) Idle speed after a set of conditions are met. I do not know exactly what those are. As fas as I can get it, there is a step motor type thing inside the IAC valve that receives pulses from the PCM and controls the air flow. Therefore this also sounds all fully automatic control.