Hi I have a 2003 Monte Carlo ss 70k. She is overheating ( not in red ) and when it gets hot it goes into a fast idle, 2000-3000 no load. Fans work on low speed but not going to high speed with over heat and when I turn AC in. They were tested with a GM tester and both went to high when tested. So I assume they work but aren't being told to. Do I possibly need a ECM or BCM or could it be something else? Plz help

Thx Gattoii

 

Could be a bad Idle Air Control valve. I don't know of any way to test it other than to clean it or replace it.

As far as overheating goes, have you checked coolant? Are you running low?

And can you elaborate a bit more on your explanation of when the fans come on? You say they don't come on when you turn the AC on or when temperature goes past a certain threshold?

As far as the fast idle goes, I think that pertains to your problem of excessive heat. It could also be that the throttle cable is too tight. When the engine is cold it should have some play, you should be able to feel it when you press on the pedal, but when the cable heats up it will slightly contract. If the cable was tensioned when the car is cold it's possible that the cable is pulling on the throttle as it heats up.

Do you have a code reader to check if there are any codes?

 

I'm thinking it might be a bad ECT (engine coolant temperature) sensor that's not relaying a signal to the PCM (ECM) to command the high speed fans to come on, or could be a bad fan control relay. Try swapping around the the fan control relays first. Then if the fan doesn't come on at low speed that's it. Doubt you have a bad PCM or you would have a CEL and DCT. The BCM doesn't control the fans, the PCM does.
As for the fast idle, I don't think it's directly related.
Like Jason said, it could be the IAC or accelerator cable, or could be the TPS.

 

changed IAC, fast idle definitely goes with the over heating as it only happens when the car gets hot. Like I said both fans work at low speed, when GM tester is used you can turn each fan individually to high speed. Something in my car is not telling them to go. Even when I turn AC on they should speed up but dont. I could try the temp sensor unit. But if you think of anything else plz help. I like the car a lot it's solid, nothing loose. But I'm on a fixed income and hope I can get this figured out with help from someone here.

Thx plz think about I will change temp sensor first.

Gattoii

 

No codes being showed, car was checked by a good GM tester, but user may not have been the best, he suggested I change thermostat but no help there. I'm just throwing parts at it cause I'm not that experienced or have equipment to to proper testing. Not much spent and car is 14 years old so some of my replaced parts were a good idea anyway.

Thx guys any more thoughts would be great and I thank you for replying.

gattoii

 

Which reminds me at first 2 years ago I thought it was the fast idle raising the temp, then winter would come and no problems, then I realized it was getting hot and then going to fast idle. Then 3 weeks ago the temp got worse, not in red yet. But both problems happen together always, must be related somehow.

thanx again trying to think or the most info I can, I need this car, to get to doctors, can't afford a new or even used.

 

Don't think you're getting the idea of swapping the fan control relays around. The purpose is to see if it makes a difference. We understand it runs on low and on high when commanded to with a GM Tech 2. The tech 2 is able to bypass the relays. It only takes a minute and is worth trying.
I do feel the problem may be with the ECT sensor though.

 

Ok wil try the fan relays, and the ECT sensor. Will get back when that's done

thx I do appreciate it

 

I think following up with the relays would be the quickest and easiest thing to check, and like we all agreed before, I think if you can get your cooling situation figured out then your idle should fix itself.

 

Thx Jason, I haven't had a lot of time, I tried swapping resisters and all fuses look good. Gonna try the ETC this weekend. Part is in a precarious spot! Any suggestions on the best way to R &R on the 3800?


Thanks again Stephen