1st post...low idle problems..help please Options

[TurboZo]

Hi, glad to find an active forum for the 6 gen celica...

I've had our (my wife's car) 99 GT for 3 years now. Since I've had it, I've been struggling with the low idle problem. On start up, the engine often stalls since the RPMs aren't high enough. At first I used to slightly hold the pedal until it warmed up. After taking the throttle body off, cleaning it, cleaning the ISC, testing it, the cold start worked for a while then started having the problem again. Currently, when starting up, it idles around 450 and feels like it will cut out. Once in a while the idle seems correct though soon it goes back down. with the AC on, at a standstill in D (auto), it starts to chug a bit since the idle is so low. Recently, I gave up and took it to a trustworthy mehcanic...he did a fuel system cleaning along with the intake cleaning. afterwards, the idle worked great...at cold start, the idle went right above 1k then eventually came down to 750...that lasted a whole 3 days...and now it is back to as I mentioned before. This issue has been driving me nuts for 3 years. I'm considering doing the seafoam manuver today.

Other things that may be related:
-some smoke at startup (perhaps aging seals, or pcv valve, or something else?)
-the engine temp stays low for quite a while, not staying at the midway mark like it did before)

Any input would be much appreciated.
Thanks,
Zo
99 GT
145k
auto