Hi guys....ok heres a ? for ya...ive read lots of you have had the same problem as im having ...i have a 2.8 auto...hmmm lets see ive replaced....cap,rotor,wires,iac valve,tps,egr valve ,maf sensor....pretty much any part of it i figured could be causing my idle to be bad at reg operating temp...only one i havent is the 02 sensor....anyone ever figure out what exactly causes this prob with the 2.8's ?....ive read alotta diff reasons all ive tried & nothin*LOL....thanx....

 

For starters there isn't just "one problem that usually causes this". Its a combination of several different things that you could loosely clump together and call "general 2.8L EFI idle malady" and it's caused by any number of things. Theres no "magic" bad component to replace, your gonna have to troubleshoot it.

What codes is your motor setting?

PCV valve, coolant temp sensor, intake air charge sensor, vacuum switch, coil, intake manifold leak, vacuum leak, fouled plug, fuel pump, fuel filter, injectors, ECM, are all things that you didn't mention that could cause "rough idle at normal operating temperature".

Whats going on is that when you turn your motor on cold, its in open loop, and not listening to the coolant temp sensor/MAF/O2 sensor inputs. When it reaches normal temp it listens to all the EFI type stuff and enters closed loop. Thats when the idle seems to change and thats when rough idle can happen.

Pull your codes and see if theres any pointers.

 

Mine was caused by a bad Intake air temp sensor (indicating hot temp. all the time) and a vacuum leak at the pcv valve.

 

Does anybody know where the Intake air temp sensor is on my 1991 Chevorlet Camaro rs 5.0l 305ci TBI?
Thanks