rdcamero

This problem does not happen until the car has been run around a 1/2 hour or more.When I come to a stop it will start out idleing fine.The idle then starts to go up and down.It will do this a few times before it stumbles and dies.If I hit the gas real quick as soon as it stumbles I can keep it running.If it quits I have to crank it for a few seconds before it will catch.
I have watched the idle air counts before and the count gos up along with the idle.Something is calling for more air when it does this.This is starting to really get to me.The car starts fine,accelerates fine and runs fine except for this idle problem.

Ken73

Bum O2 sensor maybe? That usually causes an erratic idle. O2 sensor reports a too-lean condition (because it's not putting out as much voltage) and the engine starts to die - so to keep it from doing that, it richens up the mixture and opens the IAC enough - which raises the idle. Repeat until irritated!

RRT vette

Check for vac leaks. There is a reason the ECM is commanding the IAC to search for the desired idle.

rdcamero

Replaced both o2 sensors.Still doing the same thing.I thought it may be a vac leak but it is idleing fine before it speeds up.The idle air steps stay at arount 20 and then jump up to 35 or 40.The motor is idleing smooth when it does this.The integration values stay pretty steady during this as well.

rdcamero

Hi I disconnected the iac motor when it started to speed up and down.I drove it a few miles until it got good and hot and it seemed to idle fine.It did not stumble or surge any.Could the iac valve be bad causing this on its own.

RickF

jimg's'93

hmmm...I'd guess you have a bad IAC. Just a guess.

onedef92

Try cleaning your TB and IAC motor pintle. That usually improves the base idle and stops wandering idle problems like you're having.

rdcamero

I have cleaned them a couple of times.I have also replaced all the gaskets on the throttle body.

David Joseph

This happened to me a couple of years ago- it was bad gas- if you recently switched brands or are not using premium- try going back to what you were using before

jimg's'93

The ('93) FSM also has a procedure for resetting the IAC valve:

"...depress accelerator pedal slightly, start engine and run for five seconds, then turn ignition OFF for ten seconds."

It's cheap enough to try it.

onedef92

Are your plug and coil wires in good shape?

rdcamero

Yes the wires look fine and were changed around a year ago.