'00 S10-blazer 4x4. 4.3L V6
Problem- CEL (check engine light) light comes on (TPS=trottle position sensor code) when ever the temp is between 40-50 degrees outside and the thermostat controls are set on defrost mode. Defrost mode is where I keep them all winter long. When in defrost mod the a/c kicks on to remove water vapor from the cab to keep my windows clean. When I drive with the temp setting off, no CEL.

Prior to the CEL coming on (defrost mod) I experience hard late shifts from 1st to 2nd gear. Oh almost forgot, this only happens with in town stop and go driving, or standing (waiting for the wife with the engine running while in park for 5 minutes or more). Doesn't happen on the interstate, or with the temp controls off.

So, I have a hard time believeing its the TPS screwing up. But that is the only code it trips. I think that is an after effect, however I am not sure what the cuase is. It could be a temp sensor related to the a/c system, but I am not familiar with that part of the system yet. Looking for any info to help trouble shoot the problem. I believe it has to do with the constant on/off cylcing of the a/c compressor under those conditions (ideling). It did the same thing last spring, and yet I have excellent a/c during the summer. So I don't think it is low on freon.

Any input would be greatly aprreciated.
Thanks!!!!

 

Do we have air intake valves on our 4.3's? The throttle blade completely closing or sticking in the TB?
I had one go on my Impala and it was tossing codes not indicating the IAC was the problem.

 

hmmmmm......

Good point. I'll have to check the butterfly. Last time it was sticking it showed up as a sticking gas peddle. However carbon build up in the choke area or dirty air filter could give me the same effect.

Any other ideas?

 

Bump!

 

I haven't really done a thing to it, except clear the codes. All was fine until the temp went back up, light came back on. I think tonight I'll get the code checked again to verify. Then this weekend replace the TPS. Expecting 4"-8" of snow tonight, tomorrow. Cold weather doesn't seem to affect it.