QuestionHi, I have a Ford Escort LX 1.9L Wagon 1995, stick shift (130,000 miles) with the following idle problem:
During warm temperatures (> 40-50F) the car starts OK and idle perfectly (after warmed-up) but if I press the throttle and release it the engine continue at high rev for a couple of seconds and then goes down. In the highway this is scary because it does not des-accelerates instantly.
During chilly weather (30-40F) the car start instantly, the engine goes up to 1200~1500 RPM as it should do in low temps, and it stay there for a couple of minutes (which is normal during the warm-up period). Then suddenly the idle goes down until the engine almost stall and (I think) the PCM (power-train control module) kicks in and force the engine to recover throttling it up. The net effect is the idle smoothly going up (~1200RMP) and down (almost 0 RPM). As time pass (> 5 min) and the engine warms up this up/down cycle diminish and at the end the idle stabilize in 850~900 RPM. Everything is normal after that.
During very cold (< 20F) temp (I leave in Chicago) this behavior is the same, but the idle never stabilize, always slightly going up and down.
I'd like to point out that no matter what, the engine never stalls completely.
I have another problem that might be related: a year ago the gauge temp became erratic. Now it stuck in the max position, even before I start the car in extreme cold temp. Sometimes goes down to the middle position, but short after it goes again to max or around the max position. Which means that either some coolant temperature sensor or the gauge itself is not working properly? If the same coolant temp sensor that feed the gauge also send the information to the PCM (I don't know), the computer might think that the engine is already warm and the PCM might change the gas/air mixture causing the engine to stall (because it is still cold). Since I read in this forum that similar behavior could be caused by the IAT sensor (Intake Air Temp), I'm posting this to ask you the expert before going ahead and replacing the wrong part.
Thanks in advance,
Javier
AnswerHello and thanks for the question...I'll try to help.
I would suggest a few things in this case. First, look at the over all tune up condition and timing belt of the engine. Are they in good order?
Second, take a look in to the cooling system gage problem. The needle usually never gets above the mid point of the gage. No, I don't believe that the sensor is the same one as for the PCM. It is a sending unit, not a sensor.
Third and last, I would suggest that you either bring it to a garage or rent a scan tool and check the computer system for any and all fault codes and go from there.
Hope this helps,
Erik
