My '90 Pickup, since the day I drove it home, has had an astonishingly high warm-up idle (1.5 to 2.0k), and it has bothered me all this time. It even idles as high as 2k at about 1:30PM in Texas, with my truck stewing in 101* of heat. After many hours of thinking as to what the cause might possibly be, I read a thread that stated that the 22RE has a coolant temp. sensor, and that it is supposed to have a 193* thermostat. Is this true?

My question is: Could a faulty, mis-signalling coolant temp. sensor be the cause of my high, droning, annoying warm-up idle? Should I replace the thermostat also? Would I buy that thermostat from any common auto vendor (AutoMoan, O'Reilleys, Pep Boys, etc.), or should I go to the dealership and get the sure thing?

Any other insight into this annoying problem would be useful.

Much thanks,
Donny

 

supposedly my truck is supposed to warm up @ 2600 rpm... 85 22r according to the fsm

 

actually, i don't think that's *totally* out of wack...mine (22RE) idles that high (and higher) on warmup when it's cool out...on hot days, though, it idles at more like 1200RPM until warmed up.

this question has been asked a few times on a few different forums...you get some people saying their truck never idles above 1200RPM, but, for the most part, it seems that 22REs typically idle anywhere between 1500 and 2000RPM when cold...sometimes even higher.

there is a temp coolant sensor that gives temperature feedback to the ECU which in turn affects idle speed...however, i think if the problem was with that sensor, you would likely have idle problems when warm, too...but, maybe not.

there is also an "auxilary air valve" (on the bottom of the throttle body) that opens and closes an air bypass (around the butterfly) to control the cold start idle speed. this valve works by directly sensing the coolant temp (via wax that expands or contracts as the temp changes), though.

a sticking dashpot can also cause high idle problems...i had that problem...however, in my case, those problems manifested themselves when the engine was hot, not cold.

a gummed up throttle body can also cause high idle problems as the gunk prevents the butterfly from closing all the way. (if your TB has never been cleaned, i would suggest removing it and cleaning it in any case...by now, it prolly needs it.)

a bad TPS (throttle position sensor) can also cause idle problems.

you can get a t-stat from a random parts store...according to my FSM, the t-stat should open between 187* and 194*. the stock t-stat is 190*.

personally, i would not run a 193* t-stat in texas...some people down south even like to run 180* t-stats to counter the heat.