1999 grand prix gt idle problem..

[1999gpgt]

OK so my car has 78,000 on it. its a 3.8l Nat. aspirated when its cold it runs great. but when its warmed up if i rev it to 3k it comes back down to like 450 and then revs up to like 1500 and keeps surging. anybody have any clue if its a sensor or more serious

 

[SuperSport]

My guess is the idle air controller motor may be gummed up.

 

[blueguy]

Sounds like the TPS or MAF related

 

[1999gpgt]

ok but i'm throwing no codes

 

[Liquifire]

inspect and clean the IAC. First, when it is surging like that unplug the MAF to see if it gets better or the condition remains. Go from there...

 

[Mrprez6]

I own 99 gt since 05 and experienced those symptoms comin up on 180k replaced all sensor ( Maf, iac, o2 sensors). After replacing I ran a fuel injector cleaner that's when all the problems got worse ended up having to replace intake manifold gasket and full tune up. I thought problems were done but in idle it revs itself to 2k if gas is touched by a hair falling on gas pedal. From there get ur computer reset and it should be ok. Make sure u buy replacement thermostat and parts for all that were about $250 the work is easy just get the hidden bolts inside the corners of the manifold and put back on to torque spec and pattern in teardown manual. Any series 2 3800 motor is notorious for this problem had to do my bros 95 bonneville also so if u have this motor over 125k and have funny problems that would be my guess.