CEL/Thermosensor/Idle pissing me off
 

First off, this problem (hopefully) will be fixed as soon as the dealership orders a new Water Thermosensor...but, I thought I'd throw it out there to see if there are any other possible problems:
1. Start car, engine is cold
2. After the accelerated warmup, RPMs drop down to normal.
3. CEL comes on
4. RPMs drop to about 600 or 700, or car stalls
5. When car warms up to running temp, the CEL will go off.
6. While driving around, the CEL will come on and go off for various lengths of time, but no noticeable drop in RPMs when clutch is disengaged (after initial drop - it doesn't go below 1000)

I pulled the code, and it is #9 (water thermosensor). I would like to know if replacing this sensor will cure this problem, or if the CEL and the problem I am having are two unrelated things. I am getting a Pettit downpipe installed next week, and I was wondering if maybe bad pre-cat stuff would cause this to happen, too?

I guess it's really not that big of a problem, but I hate sitting around until the car is warmed up fully before I drive it anywhere. If I don't, I run the risk of stalling while driving, which is not fun (takes a little bit to get it going again). The sensor I am getting for free, because the dealership f'd it up when they f'd up the engine.

What do you think?

- Tyler

Anyone?

Could someone please give me some input?

I cannot (and will not) believe that no one here has any idea about this problem. PLEASE, I am begging you for your input on this problem

:( Tyler

Well, I think no one is answering because we all think you should get the thermosensor replaced and/or check the wiring for continuity to make sure the signal is being seen by the ECU. This should of course stop the CEL code #9 issue, and all should be ok after that. Is it possible you are experiencing the CEL independent of the thermosensor problem and subsequent code #9? Sure, but you won't know until you've fixed the thermosensor and are no longer pulling code #9.

My guess is that during warm up, the thermosensor signal is not reaching the ECU at some point, and when that occurs, the ECU decides to alter the idle and fuel mixture to compensate for possible too cold engine. I'm going to guess it just reverts to a rich condition, which kills combustion until the engine really IS warm. At that point, the ECU is still most likely running rich, but the engine temp supports combustion, and that's why it runs ok. I'm pretty sure the DP situation has nothing to do with it. I'm also pretty sure that the f***ed up install from the dealer may have caused a problem in the wire that carries the thermosensor signal. If they put a new engine in, but did not replace the thermosensor, well then, it might just be a bad thermosensor. But it might not.

So replace the thermosensor, and then clear the ECU codes (negative battery cable disconnect followed by pressing the brake for 30 seconds, then re-connect the negative cable), then re-start the car and see if the ECU throws the code. Or have the shop that's doing your DP do this. But this is a pretty simple operation (swapping the thermosensor), so you might want to start here on the long tortuous road to self repair... just my $0.02

If the thermosensor replace does NOT fix the problem, then it's the wiring. Get a multitester that gives a beep when continuity is tested. Place one test lead to the connector, and the other to the pin on the ECU that carries the thermosensor signal. See if it beeps. Try this with a cold engine, then try it with a hot engine. Note that you need long test leads for this, and you need to look at the manual to find the pins.

Yes, those symptoms could very well be caused by a bad thermosensor. I know rxplicit had the exact same problem and symptoms (I think he responded to your other thread?). Replace the sensor and if it's still acting up, let us know.