Idle air control valve: does it cause this?

[98_Q45]

Generally on cold days/cold starts...after driving for 1/4 mile and coming to a stop/slowdown, the Tach will start moving up and down below 1,000 RPM, engine shakes and TCS/Slip lights blink at once, even a bit of bucking coming from the rear transmission. Sometimes it’ll just stall out completely unless I shift it into neutral.

Once the engine warms fully, it no longer does it. However lately, it used to do it only below 60 degrees outside, now it’s doing it all outdoor temperatures...until it fully warms up.

I replaced with a salvage IACV just to see what would happen, it still does the same thing. Can’t find anything on the service manuals that address how to adjust or clean the IACV.

The part itself new checking Infinitipartsdeal and auto parts stores shows $300+ for that valve. So, if I go that route I’d rather be sure that’s the cause...and not something like the MAF or other sensor.

[3Q Jay]

poor man's way:
when fully warmed up, unplug the ECU control connector to the IACV (engine running at idle, no AC, in park), adjust set screw to achieve 600 RPM (tool better than the dash tach is preferred). then plug connector back in. there will be a brief surge, then it should settle out at ~625 rpm.
Better way is with a consult interface:
the '98 should still have the OBD-i connector under a trap door right under the steering column.
adjust for 12% duty cycle at idle--same conditions.

[98_Q45]

Thanks...I’ll try this. So that screw is it normally closed or open when looking inside the IACV?

[3Q Jay]

partially open. think of the mixture adjust screw on an old carburetor.
don't forget new gasket when you pull or replace the IACV (not necessary for just external adjustment on the car). those gaskets can have small air leaks and mess with stuff.

[98_Q45]

Thanks. Well it is a metal gasket, I figured it didn’t need changing.

Well, so far I’ve sprayed some throttle body cleaner in there and I also cleaned the throttle body as well...as it’s been awhile. It seems to have stopped the issue...but it still does it a little bit...notably after doing gas refills and even after a cold car wash. It seems to be something else more specific with cold weather/cold fuel causing it.