It seems that my car a 94 z28 auto runs perfect until it gets warmed up and the idle drops from around 800-900 to 500 RPM.
When it is warmed up the idle gets rough. Is this the correct idle speed or not? Please advise on solutions/ problems.

Thanks Robert

 

Check out your Coolant temp sensor on the pump. Intake air Temp sensor is another possibility. Maybe more than the other. You might hook up a scanner if you can and look at the data. That would help alot. Correct idle is 800-900 I believe.

 

ohh mines 500 too... hrmm i need a scanner

can u buy scanners?

 

Theres alot available. Hypertech, LT1 Scanmaster, Auto xray, etc etc. Research it for the best one for you.

 

The factory programmed idle speed for an A4 (what he has) is 550rpm in gear, and 650rpm in neutral. Remember, the stock tach typically reads 100-200rpm higher than actual engine speed. The idle speed will not drop to the above figures until the coolant hits 176degF.

Only the M6's are programmed for 800rpm idle.

There is a table of the typical factory idle programming, as a function of coolant temperature in my ScanMaster writeup.

 

to get to the iat do you have to remove the throttle body or is that the iac valve

 

oh ok i know that answer now, but can i use electrical component cleaner on that

 

The IAT (inlet air temp) sensor is stuck into the side of the inlet bellows (elbow). It is easily accessible without moving anything. Not sure whay that would affect idle, either speed or roughness on a mass-air car. IAC (idle air control) is on the bottom plate of the throttle body. Coolant temp sensor is on the front of the water pump housing. A scanner will easily tell you if the IAT and coolant temp sensors are working correctly. Alternatively, simply measure the resistance of each, to see if it is consistent with the temperature - again, there is a table of sensor resistance vs. temperature in my ScanMaster writeup.

 

so when my idle says 500 its really 300-400?

its ususally not rough but some times the needle will touch the 500 and it shakes the whole car and the needle goes back up to about 525 or 550