90 LS, @ idle, my rpms fluctuate up and down. Sometimes it stops but most of the time it hits around 1500 rpms then falls back down and then goes back up. This problem occured right after I got my timing belt changed. I already check my Vacuum hoses and I do not have a leak. What else could it be, anyone else had this prblm b4? I think its my Timing *shrug*

Thanks,
Steve*

 

Hey what's up man! I have a G2 and I think i had the same problem... Right before my alternator went bad it was ideling funny just like you posted.. I then did tests on it to see if it was the alternator and the tests proved it to be good.. After a week or two of not finding an answer as to why, I tested it again and i needed to replace it... After that it ran fine..... ???? sounds stupid don't it.........It could be that, or it can't be that. Try testing it. Also is ecu showing any codes?? Oh, one last thing....Did you check the idle control valve??? Anyway, if you find out what is going on with it let me know cause I'm buying a 91 LS beater with same problem and if its something different let me know. later,evan

 

COuld be a number of things.
Fast Idle thermovalve FITV
IAC valve
bad ECU
air in the coolant

They are all possibilities but the first 2 are very suspect.

 

all these could be the reason.......also, maybe your timing belt was installed improperly and your motor could be out of time........if so you would feel a good loss of power