My idle fluctuates between 1300 RPM and 1500 RPM until the temp gauge reads halfway between H and C (i.e. normal operating temp). Then when warm it holds an idle at 1000 RPM. If I screw the idle mix screw in, it will stop fluctuating when cold, but won't idle for s%$t when it is warm (i.e. at 200 RPM!!!!!!) WTF?

 

What year is your car?

 

got same problem on my '90 gxl. i think its the thermowax. any write-ups on how to fix it?

 

my 90 gxl does the same thing pretty much. it has always started up fine for me and the rpms jump up when the engine is cold, and that part is normal. Then after the car is warmed up and i am driving it i stop with the clutch in and all and the rpms go down to like 600 or so and it kind of slowly bounces up and down from 600 to 900. Sometimes though the idle is around 1000 rpms. without the lights on or any electrical stuff the car seems to have a higher idle, but i am kind of concerned my idle is too low because with the lights on and stuff the car seems to idle too low.

 

I heard this is a sure sign of a bad alternator; but I'm not sure if I agree with that. The low idle might be caused by your throttle position sensor; once I adjusted that it seemed to level off some when the car warmed up. But I'm almost positive the warmup fluctuations are caused by the thermowax.