ChokolAwt

91 civic dx converted to mpfi. car runs and drives great, but when the motor is finally warmed up, and i take it out for a spin, the temperature gauge drops back down to cold, and upon reaching a stoplight or stop sign, the motor revs up to 2k thinking its still warming up. the idle will eventually settle back down to ~750rpm (takes a minute or two) and the temperature gauge with come back up to just below 1/2 (where its always been before i did the mpfi swap) but as soon as i get moving again, it cools back off and repeats each time i stop.


could this be a thermostat stuck open? i've had a thermostat get stuck open on my old crx but it would just never warm up at all.

Fabrik8

Most likely the thermostat is stuck at least partially open. It sounds like there is enough coolant flow to overcool the engine when the car is moving, but not enough to prevent it from getting close to normal operating temperature in the absence of airflow. Luckily thermostats are cheap and easy to replace, and also easy to inspect and test.

ChokolAwt

so a quick google search yielded a redneck and a videocamera. any tips/tricks to this?


http://www.youtube.com/watch?v=_z4xhbPdcMU

Fabrik8

If you have a candy thermometer or meat thermometer it would help, but it's not really necessary. Even though it's a good idea to test the old thermostat, I usually don't remove an old thermostat without putting a new one in. It's a good idea to test the new one while you're at it also, just to make sure it works before you button everything back up. It's an extra step I know, but it's an extra just that only involves heating some water on the stove so you might as well do it while you're already in the kitchen cooking dinner or whatever.

ChokolAwt

okay thanks. i'll check it out tomorrow. turkey time!

gameoverr96

i think youre having problems with your engine coolant temp sensor

Fabrik8

There are separate sensors for the ECU and the temperature gauge. If the temp gauge was showing a problem because its sending unit was faulty, the ECU should be running the engine like nothing is wrong. If the coolant temp sensor was faulty, the ECU would run the engine like it's not warming up but the temp gauge would show nothing is wrong.

ChokolAwt

im assuming this is a good thermostat?

I removed the IACV and filled it with carb cleaner and few times. some threads are saying to leave it soaking overnight to make sure it's clean but i dont have that kind of time.

Also the idle is super high when the car is cold now. it'll rev up to 3k when i first turn it on. once the temp gauge comes up a little (still not where it normally should be) the idle will settle down to like 1.5k-2k but no lower. plugging the bottom hole on the inside of the throttle body settles the idle down to ~750rpm. i've screwed the idle adjustment screw all the way in, but nothing happened.

Fabrik8

So the idle changed after you made no changes except cleaning the IACV?

ChokolAwt

well it could have been any number of things. i removed the iacv again and dunked it in a bowl of brake cleaner, while the thermostat was boiling, while i was cleaning the FITV... so whatever one of those was clogged/dirty and causing the high/surging idle, is now fixed.

car runs great! thanks fabrik8!