Intermittent Stalling Problem

[Oil Changer]

Had a detailed post written that got lost in Internet cyberspace.

Cliff note version:

Car stalls at idle when warm. No CEL or codes. Sometimes starts right back up, sometimes very difficult to re-start. Visual inspection showed nothing out of the ordinary.

Would like to know if anyone else has had this problem and what fixed it; point me to something I missed while searching this forum, and/or offer ideas.

2008 Aveo 5 Special Value
E-Tec II 1.6L
5 speed manual
100% bone stock.
Very well maintained
59,100 miles

[petrified.rabbit]

there are a few things this could be are you able to test anything or are you going to throw parts at it?

[Oil Changer]

there are a few things this could be are you able to test anything or are you going to throw parts at it?

I am able to do some minor testing. I'll throw parts at it if the price is right. I'm open to all ideas right now.

[wuwei37405]

I would guess (and I do mean guess) that it is the ignition coil. They are not cheap by my standards, costing from $65 to $95. So, I am asking, "Do you want to spend that kind of money on a hunch?" Also, if the wires and plugs are old, you might want to replace them at the same time. Good luck. If you try it, and it doesn't work, I apologize in advance.

[Oil Changer]

Still here. Welcome any responses. Car still stalling at idle when warm only. Plugs/wires changed about two months ago with Bosch Iridium/BWS wires.

Smell coolant but see no leaks/wet spots/drips. Level still normal to high.

The only thing that has changed is the weather; 30 degrees F or less typical average now.

Runs like a champ when at any RPM other than idle.

Rough idle (but not extreme) and idle dips real low when trying to stop for light/sign/traffic. Lights on/high heat (eg. high electrical demands) does not seem to matter.

[wuwei37405]

You smell coolant. Check the spark plugs. If any of them have coolant on them, you may have a head gasket leak. Again, good luck.

[petrified.rabbit]

it sounds like the car is not going into "high idle" for the cold weather, there is a temp sensor for that. The problem is it happens when it is warm, not on initial start up? So that could be the AIT sensor, or even just a leak in the intake pipe nearby.

the issue really is an idle issue, so vacuum leaks, idle switch sensors, tps, or a dirty throttle body could be suspect.

[Oil Changer]

it sounds like the car is not going into "high idle" for the cold weather, there is a temp sensor for that. The problem is it happens when it is warm, not on initial start up? So that could be the AIT sensor, or even just a leak in the intake pipe nearby.

the issue really is an idle issue, so vacuum leaks, idle switch sensors, tps, or a dirty throttle body could be suspect.

Fires right up every morning and after work when it's been sitting all day. I'll let it warm up for at least 15 minutes every morning and it has yet to stall. To repeat, the only time it stalls is at idle after the engine is throughly warm.

Example: Leave work, start car, idle for a minute, drive 3 miles surface streets to express way ( no problems), drive 10 miles express way and exit, drive surface streets, stalls at lights/sitting in traffic. Not every time. Sometimes it starts to shudder and I can save it by bringing it off idle, sometimes stalls with no warning. When trying to re-start, it will either fire up with a little longer than normal crank or on a couple of occasions, I had to push the car off to the side and wait a minute before trying to re-start, which it does; sometimes immediately, sometimes with a little effort.

When at speed, the car runs like a clock. No loss of power or fuel economy. No CEL or codes.

[petrified.rabbit]

it is unlikely that they created a running issue like this, accidentally.

if you are looking for damage, that has your running issues and the lift in common, check the fuel/vapor lines and such under the car to see if they have been pinched or crushed, etc. even the underside of the gas tank, etc.

[Oil Changer]

Update:

Same story. Stalled once coming home. Re-started with only a slightly longer than normal crank. Stopped at a store and five minutes later started and ran normal. Drove home less than a mile a way. Was going to leave running to see if it would stall during the time it took to check the mail. Never made it out of the car. Stalled, re-started almost immediately. Ran out to look under the hood. Stalled again before I could get hood up. With hood up, tried to re-start. Cranks hard/fast but no start. Went out 30 minutes later crank hard/fast but still no start.

What about the oil pressure sending unit? Will a faulty sending unit shut off the engine like what is happening w/o throwing a code or the CEL? And yes, the oil level and type is fine. 5W-30 Pennzoil Platinum w/AC delco filter with less than 5000 miles since change. Dipstick up to top and normal color/smell.

I ask about the sending unit because when I was cranking, the oil light was flickering. It did, however, go out after my second extended cranking session which to me indicates oil pressure and a working sending unit. I only ask because I never noticed the light flicker like that. Then again, I never had to crank it like that either.

I'll attack it hard tomorrow and post anything I find.

Many thanks to the two participants trying to help.