surging idle

[jeffgrice]

Hi,

I have a 91 vert with base motor and 30k miles.

Done a complete tuneup, new injectors, EGR, removed cats (clogged), etc.

The car runs awesome especially with the computer tune done.

But, sometimes at idle it feels like it is surging slightly...or hunting for idle speed.

When I turn on the AC it runs totally smooth....no hunting. I am told that confirms the IAC is working.

It is not throwing a code. I have had it suggested that it is the O2 particularily since the car was running rich from bad injectors, clogging the cats that the 02 code be going bad or carboned up.

When it does hunt, after jumping on it it smooths out for a while.

Does this seem to point to the o2?

Thanks.

Jeff

 

[jimmers]

im curious to know the answer to that aswell. My 90 does the same thing.

 

[Hrtbeat1]

Have you replaced the Intake Themistor (two pronged electric termostat under the TB)? It can work well in some ranges but incorrectly in other ranges.


Possibly the O2 sensor.

Either one is pretty easy.

 

[mdsbch]

Have you checked your vacuum hoses. My 85 used to hunt at idle, it would go from 550 to 620 rpm back and forth. It seemed to do it more after the car had been run for a while then shut off for about 15 minutes and then started back up. I found a leak in the vacuum line going to the cruise control unit and replaced it. I'm not sure why a leak would cause it to hunt. I thought a leak would just cause it to run bad, but it seemed to fix the problem.

 

[WaveDoggie]

Nail down all vacuum leaks, ensure the TPS voltage is rock steady, then tweak the EGR valve and be sure it is sealing at idle.