ckinart
New Member
Hi all,
I've been experiencing trouble with my '94 MTX only when it's cold. About a week and a half ago (after only driving the car for about 2 minutes) I was idling waiting to make a left turn in traffic when suddenly the idle went up to about 1800 RPM on its own. When I proceeded to make my left turn, as soon as I applied throttle the engine nearly stalled, was extrememly sluggish and the CEL came on. I managed to make the turn and rolled to the side of the road. About 10 seconds later, the CEL went off and everything returned to normal. I checked the codes and only got a 118 in continuous memory (ECT sensor is/was high or open); passed both the KOEO and KOER tests, but of course at that point the engine was warm. Then, all last week with the colder weather, when I first start the car it runs very rough for the first 30 seconds or so, in a way I can only describe as a "bap bap bap..." instead of a smooth idle. Then the engine will run smoother, but the idle will be very erratic moving (on it's own) from 1100 up to 1900, stay there for a bit, then fall to 1300 and wave between there and 1500 for a bit, etc sometimes dropping off to nearly a stall, and then recovering. Any applied throttle nearly stalls it. If I leave it for about 10 to 15 minutes until the temp is in the "normal" on the gauge, everything is perfectly normal. I can drive it fine, and performance is as good as ever.
Now, I replaced my ECT sensor about 3 weeks ago because I was getting an intermittent CEL for 173 and 177 (rich rear and front banks). I have since switched out my IAC with no improvement (reset the idle afterwards), and tested the TPS which puts out about 0.96 V at idle and, from what I can tell, a linear response through the entire throttle range. I've shifted all of the wiring harnesses while this behaviour is exhibited looking for any change, but to no avail. I've cleaned the MAF, as well as unplugged it when the engine is cold, but the idle is still erratic.
The only ideas I have left are that some sensor is on the fritz and is only affected when cold, or there is a ground to the engine somewhere that is getting better contact when the engine warms up, or perhaps I have a vacuum leak that is closing up when the engine gets warm. But then there's that strange 118 code I got last week...
Anyone have any other thoughts or ideas that I could check out? I'm at a bit of a loss here. All I have to do is basically ignore the erratic idle until the car warms up, but needless to say I'd like to fix this problem ASAP.
By the way, I have not replaced my crank or cam sensors, but I'm not sure that's relevant (just thought I'd add that). That's all I can think of for now. Sorry for the long post...
Any suggestions or pointers would be greatly appreciated!
<small>[ January 11, 2004, 02:25 PM: Message edited by: ckinart ]</small>
I've been experiencing trouble with my '94 MTX only when it's cold. About a week and a half ago (after only driving the car for about 2 minutes) I was idling waiting to make a left turn in traffic when suddenly the idle went up to about 1800 RPM on its own. When I proceeded to make my left turn, as soon as I applied throttle the engine nearly stalled, was extrememly sluggish and the CEL came on. I managed to make the turn and rolled to the side of the road. About 10 seconds later, the CEL went off and everything returned to normal. I checked the codes and only got a 118 in continuous memory (ECT sensor is/was high or open); passed both the KOEO and KOER tests, but of course at that point the engine was warm. Then, all last week with the colder weather, when I first start the car it runs very rough for the first 30 seconds or so, in a way I can only describe as a "bap bap bap..." instead of a smooth idle. Then the engine will run smoother, but the idle will be very erratic moving (on it's own) from 1100 up to 1900, stay there for a bit, then fall to 1300 and wave between there and 1500 for a bit, etc sometimes dropping off to nearly a stall, and then recovering. Any applied throttle nearly stalls it. If I leave it for about 10 to 15 minutes until the temp is in the "normal" on the gauge, everything is perfectly normal. I can drive it fine, and performance is as good as ever.
Now, I replaced my ECT sensor about 3 weeks ago because I was getting an intermittent CEL for 173 and 177 (rich rear and front banks). I have since switched out my IAC with no improvement (reset the idle afterwards), and tested the TPS which puts out about 0.96 V at idle and, from what I can tell, a linear response through the entire throttle range. I've shifted all of the wiring harnesses while this behaviour is exhibited looking for any change, but to no avail. I've cleaned the MAF, as well as unplugged it when the engine is cold, but the idle is still erratic.
The only ideas I have left are that some sensor is on the fritz and is only affected when cold, or there is a ground to the engine somewhere that is getting better contact when the engine warms up, or perhaps I have a vacuum leak that is closing up when the engine gets warm. But then there's that strange 118 code I got last week...
Anyone have any other thoughts or ideas that I could check out? I'm at a bit of a loss here. All I have to do is basically ignore the erratic idle until the car warms up, but needless to say I'd like to fix this problem ASAP.
By the way, I have not replaced my crank or cam sensors, but I'm not sure that's relevant (just thought I'd add that). That's all I can think of for now. Sorry for the long post...
Any suggestions or pointers would be greatly appreciated!
<small>[ January 11, 2004, 02:25 PM: Message edited by: ckinart ]</small>
