Air conditioning on, car randomly stalls at idle

[opethmike]

So I've got a really strange one that just started cropping up a few weeks ago.

If I have the A/C running, the car will randomly shut off at idle. There won't be any surging, juttering, anything like that, it just shuts off as if I had turned the key.

While driving with the A/C, the car will keep running and driving (thankfully!), but I can feel a little surge whenever the compressor cycles.

No clue where to start searching on this one.

My car is Megasquirt EFI + idle control. I have made zero changes to the tune this year, so I am doubtful it is anything in there.

[Rich W]

Hi Mike,

I have seen the same type of issue on another DMC club member's car. Stock K-Jet PRV, 5-speed, engine stalls intermittently at idle, only when AC is on.

I have seen the engine stall while at idle (in neutral) or when coming to a stop (previously at speed) taking foot off gas pedal and depressing the clutch pedal.

This issue first cropped up during the July 4th parades, a little over a month ago, but the intermittent stalling problem still persists.

With the AC off, engine runs fine and does not stall ... idle remains smooth, either in neutral or with clutch disengaged.

I am planning to investigate the issue further after the Woodward Dream Cruise this upcoming Saturday.

Later,
Rich W.

So I've got a really strange one that just started cropping up a few weeks ago.

If I have the A/C running, the car will randomly shut off at idle. There won't be any surging, juttering, anything like that, it just shuts off as if I had turned the key.

While driving with the A/C, the car will keep running and driving (thankfully!), but I can feel a little surge whenever the compressor cycles.

No clue where to start searching on this one.

My car is Megasquirt EFI + idle control. I have made zero changes to the tune this year, so I am doubtful it is anything in there.

[Bitsyncmaster]

My guess to the problem would be the sudden current load when the AC clutch and fans kick on at once. You probably have a bad connection (maybe a ground) that drops to much voltage and you ECU just cuts out with that low voltage.

[David T]

My guess to the problem would be the sudden current load when the AC clutch and fans kick on at once. You probably have a bad connection (maybe a ground) that drops to much voltage and you ECU just cuts out with that low voltage.

I agree but it could be even more subtle than that. At idle the alternator can't out out as much so you wind up running on the battery. Even without the fans and compressor hitting hard on the electrical system, with the alternator unable to keep up with the load, the battery voltage will drop to a critical point and the ignition ECU will call it quits. Any bad connection will only make things worse.

[hmcelraft]

I have had that symptom before. It was after I had replaced the micro switch and I messed with the adjustment. The adjustment for the micro switch is important as to timing for turning on the idle speed motor. Turning it on too soon causes the engine to stall - to late and you get a run-up in the engine. I think I got that right? Anyway, after I adjusted the throttle movement everything went back to normal. Look on page D:04:15 of the Workshop Manual - Spec 3.

[hmcelraft]

So I've got a really strange one that just started cropping up a few weeks ago.

If I have the A/C running, the car will randomly shut off at idle. There won't be any surging, juttering, anything like that, it just shuts off as if I had turned the key.

While driving with the A/C, the car will keep running and driving (thankfully!), but I can feel a little surge whenever the compressor cycles.

No clue where to start searching on this one.

My car is Megasquirt EFI + idle control. I have made zero changes to the tune this year, so I am doubtful it is anything in there.

Oops - Megasquirt! Never mind

[dmc6960]

I had an issue like that back in 2010, that one was caused by low voltage causing the Megasquirt computer to shut down. I could see it in the last few frames of the log the voltage dropping during the stall.

Lately this year, I've been having a similar issue, but this one is not voltage related. I believe my OEM idle motor (I'm still on stock idle control) has gummed up and is not responding properly to input from the computer. Under a light load I'm getting oscillations I've never had before, and under a heavy load (AC on) it tries to stall entirely. It still seems to rotate freely by hand, but after 140,000 miles, it really could be at end of life. Of course, that is only a theory until I actually try to fix it.

[opethmike]

I think Mr. Reeve may be on to something here. While I was running the car yesterday, waiting for the stall to happen, I noticed that my idle voltage was only 13 volts. I didn't see the gauge in Tuner Studio drop when the car shut off, but after reading Jim's post, I examined my log closer and found that voltage did in fact drop, just about an entire volt, at the time of shut down.

So for shits and giggles, I put my spare battery on my charger over night, and installed it today. At idle, I found I was now, on the "new" battery, getting 14.4 volts at idle. I could see the voltage drop down to ~13.5 when the A/C compressor would cycle, but the car never stalled. Granted, I didn't run it for particularly long today, but this makes me think that the weak, "old" battery combined with the drop during cycling is what was causing the stall.

Still, that seems like a pretty brutal voltage spike from the compressor cycling. I cleaned every single f'ing ground on the car last year, so I doubt that it is a grounding issue. If/when I improve that voltage drop, I'll let everybody know the solution.

[mluder]

Slightly askew from topic... Anybody ever have an issue with an idle surge as you come to a stop?

My car will be running along just fine and as I come to a stop I get a slight idle surge to about 1200 RPMs and the it sits down into normal idle. More pronounced when the AC is running but it does it whithout the AC as well.

Thanks

[Bitsyncmaster]

Slightly askew from topic... Anybody ever have an issue with an idle surge as you come to a stop?

My car will be running along just fine and as I come to a stop I get a slight idle surge to about 1200 RPMs and the it sits down into normal idle. More pronounced when the AC is running but it does it whithout the AC as well.

Thanks

It depends how you drive your car. If you decelerate until the engine is below 775 RPM and then hit the clutch it would probably surge on most cars. It's funny how each driver will shift the car different from other drivers. I tend to step on the clutch at 1500 RPM or there about. I don't use the tach for my shifting, just the sound and speed.