-98-Z28-Darkness-

iTrader: (7)

my car started acting up this month i turn on the car and leave on park the idle goes down to a stable 800-900rpm,

have not changed anything at all on the car, now once start driving it will idle at 1500rpm, but once i let the car idle for about 5 seconds at a stop it starts surging from 800-1100 but if i put it back in park it idles nicely at 800rmp again,

i do get a iac code, so i switched the idle air control but had not difference. i also cleaned the Mass Airflow Sensor, throttle body, and filter, also checked for intake leaks.

The car runs great, this issue just bugs me! thanks for the help

ShevrolayZ28

iTrader: (4)

you sure there isnt dirt clogging the little air passage to the IAC? You could spray some carb cleaner thru there if you havent already. is the IAC code gone now?

Big&Tasty TA

It sounds like it is "parameter hunting", either some sensor isn't reading right whether it be a mass air sensor, etc. The computer is trying to fix the problem and is overcompensating adjustments, which causes the surge" up and down in rpms". Other causes for parameter hunting are vacuum leaks, and sometimes stuff as simple as a dirty air filter or even bad gas. The vacuum leak can be extremely small and still cause the engine to hunt. Before replacing any parts, I would run some new gas through it and also check for vacuum leaks. Check everything, even dipstick tubes can cause this, I have personally seen it happen. Hope this helps and good luck.

Steve Gunn

I agree with a vacuum leak. The most common culprit is the cheezy PCV system. Spray everything down with carb/choke cleaner. When you hear the idle change while spraying, you've found your leak.

poltergeist 02

iTrader: (65)

could be a bad throttle position sensor or map sensor. i would think the map would throw a code though. so maybe tps sensor.

-98-Z28-Darkness-

iTrader: (7)

cool i will check leaks the carb cleaner way, i got a 98 ls1, i redid my pcv system closed the passenger pcv tube and got the driver side tube running into a catchcan into to the TB, but its been on for a good 6 months with no problems.
thanks for the advice
only reason i dont think it is a leak is because today in the morning it ran perfect and in the evening it started up again! maybe it only happens when the car warms up...

sjsingle1

iTrader: (1)

intake gaskets could have gone south.....ask me how i know

-98-Z28-Darkness-

iTrader: (7)

well went to work around 2 still acting up but at 9pm cooler then most night and even some rain, the car was running perfect! I must me weather related some how.....