I purchased my 91 Z28 in feb. of this year. and ever since ive noticed the car has an "erratic idle" the rpm's will rise then drop, etc. etc. If anyone has ever had this problem i could use some advice. (Note: the car only has 40k original miles)

 

sometimes its cuz of the poorly placed MAT sensor its located too close to the engines heat causing it to give the ECM incorrect readings id suggest relocating your MAT sensor its on one of the articles in the tech section i believe

 

ill look into that... cause the car runs great throughout the throttle band... hell i had it up to 135 last week running a mustang.... but its just the idleling thats the problem... that and overcooling....

 

sounds like the situation is that your ECM isnt getting proper information and running rich id also check fo small vacuum leaks that have occured over the years if there is any noticeable cracks or rot make sure to replace em

 

What they said also check for fuel pressure. mine did the same when I had to drop the fuel pressure to pass emissions.

 

The IAT won't make it a sloppy idle. Heck they run fine were they are so why change it. People just do that to richen the A/F up a bit .

Any codes ? I am leaning towards the MAF buroff relay or a sticky IAC valve

 

no... no service engine light no codes coming up.... thats why im so confused... its as if it has a blower or something cause the rpm's just rise and drop rise and drop etc. etc. but it runs damn fine throughout the throttle.... it is possible that it may have a 160* stat cause the car is also overcooling so i hope to change it within the week... cause i heard if a car has one it could mess up the performance cause it feels like the car is staying in "warm up" mode.... runnin slightly rich... so i dont know.

 

Assuming that the car is getting into closed loop, try cracking the throttle blades open a little - using the hex set screw on the throttle cable linkage (shut the engine off before making any adjustment). The computer will keep the idle speed correct, so you don't have to worry about the RPMs.

That solved a really erratic idle on my 92Z - but then again mine is reasonably modded.

Good Luck.