I am going nuts and losing my patience chasing this idle fluctuation. I have throughly cleaned out TB, including section that contains the adjustment knob,
along with new gaskets. TPS is properly adjusted. Last sunday night I disassembled the IAC and thoroughly clean it. Plugged connector to it, while I plugged both IAC hoses to check for correct operation of it as I opened and closed throttle. IAC still a bit sticky opening and closing. Purchased new one from Groton. Installed yesterday. Idle quality and smoothness has improved, but RPM up/down cycling still present.
Big turbo hoses are less than a year old. I have checked other hoses for vacuum leaks and found none. Injectors cleaned and tested this summer and installed with new seals. Car (89 745,129K, meticulously maintaned) runs great except for this.
What to check next? I am going to removed and surgically inspect each vacuum hose. I read in the archives of same problem solved by changing the intake man.
gasket. Also an earlier post yesterday mentioned fuel pressure reg.
Possible BIG hint: car idles silky smooth when cold. When operating temp is reached idle quality declines.
Any one have any suggestions on what could be causing this? Thanks for any help in advance and also for all great advice I've received in the past.