Contour Enthusiasts Group Archives Forums General Troubleshooting Won't hold idle when warm

MORE problems. this car is SOO close to going off a cliff right now.

anyway... i finally drove it for more than 2 miles at a time... this trip was 6 miles. by the end of the trip, it wouldn't hold idle. the rpms would drop low and it would just die. it would start immediately back up, and then die again unless i manually kept the revs up. it will drive just fine as long as i don't have to sit and idle (traffic lights)

i'm wondering if this isn't my alternator, perhaps? hopefully it's nothing worse...

my car is as follows:
99 cougar
3.0L hybrid
24# injectors
ProFlow 75mm MAF (calibrated to match)
Ford Motorsport 9mm plug wires
new PCV valve

i can't think of any other pertinent information at the moment. i also haven't actually checked/tried anything yet, as i just got home, i'm tired, and i'll start in on it tomorrow. but if i could get a starting point perhaps? i would seem to think the "after driving for a little while" would be the key point here, because since i finished building the engine, i've not driven more than 2 miles at a time.

There have been many problems lately with Pro-Flow having bad calibration data. The enrichment durring warmup may be allowing it to idle. Other than that, it may have a vacuum leak somewhere.

A scan-tool would tell you pretty quick if the mixtuer were way out.

so what you're saying is that it could be running it nice and rich when i first start it, but as it warms up it's leaning out and that's what's causing my car to stall at idle?

i haven't gotten on the throttle more than 30 or 40% yet, but if i did, would this also cause detonation at a larger throttle percentage? i had some pinging before (more than 25% throttle), but i was convinced it was because i had leftover 87 octane in the tank when i added some 93. once i added more 93, the pinging went away, at least at the amount of throttle i'm giving it.

Unless the compression is much higher than stock, the mixture alone may not cause much pinging except at full throttle. If you have the 2.5L EGR installed you may be short on EGR flow.


It would be best to verify the MAF calibration or check mixture via the PCM with a scan-tool.


Too many people have been sending Pro-Maf 75's back for recalibration. Sometimes more than once.

Check with the 3.0L section for more info.

I had the same problem on my car after changing a water pump. Turned out I knocked a hose loose and had a vacuum leak. I'd check that first before anything else, as it's a fairly easy & cheap fix.