Please Help! Stalling, violent idle, no acceleration

[avguy]

.... What are your thoughts on that?

If you're ready to let a shop figure this out, then find a mechanic who is capable and willing to diagnose, as he should be doing, instead of throwing up his hands and guessing. ECM/PCM is always the very last thing on my list of suspects (right there with bad gas), and I've seen far too many cases where they say ECM when they simply have no clue what the actual problem is. The temporary performance improvement from the new coil/wirse IMO virtually rules out the computer as being the issue. In your place, I'd run the tests I suggested previously, and continue testing as necessary until the problem is diagnosed. But of course not everyone is willing or able to invest the amount of time that I do. Your vehicle, your choice.

[Chrisj4269]

Spark seems slightly weaker on two cylinders but plugs, wires, and coil are all new. At this point it literally starts and idles for maybe 10 seconds then fumbles and dies. Touching the accelerator instantly kills it. It's still daylight but even misting had no effect when I did get it to idle

[avguy]

Are the spark plugs wet with gas, or are they dry? Also, are there any abnormal deposits on them?

[Chrisj4269]

They do not seem wet and no deposits noticable.

[avguy]

Having performance improve like it did has me wanting to eliminate a number of possible suspects, which isn't necessarily a good thing to do. I had been focused on the bad spark path, but if spark is the issue, I'd be expecting the plugs to be at least somewhat wet with gas after it stalls out. But this gets a bit muddled because the ECM can shut down the injectors if it detects major misfire. However, with no misfire codes showing up, a shut down of fuel delivery by the computer doesn't fit very well either.

So what I suggest you try next is to spray a SMALL bit of sensor safe starter fluid or carb cleaner into the intake, in order to see how it runs on that. You can try to see if it will rev up just a bit with a small amount of outside fuel when you hit the gas pedal, which from what you're saying it will no longer do at all.

I did see that you ran a test that showed good fuel pressure, but since it appears there is spark, IMO it's important to confirm that fuel delivery isn't the problem, by showing that it won't run any better with outside fuel added. You'll naturally need a helper to run the engine while you spray the fluid in. And of course it's not intended to run the engine for any significant length of time, just to check if performance perks up noticeably on outside fuel. Depending on what that test shows will determine what to do next.

[Chrisj4269]

I did the starter fluid test this morning and before my wife could even put pressure on the accelerator it died. Even a very light spray kills the car instantly. It seems to definitely be spark. At this point it's got a new ignition coil (replaced twice to insure I didn't get a faulty one), new copper plugs, new ngk wires, new cam position sensor (replaced twice to insure I didn't get a faulty one), completely cleaned throttle body, new intake air temp sensor, new MAP sensor and vac line, and as of yesterday a replacement (from used car) PCM. It still will not stay idling for long without chugging terribly and dying. Pressing the accelerator is a death sentence immediately. I have also tried unplugging crank position sensor, removing the exhaust pre cat (insure it wasn't plugged) and it had no effect. I have rolled engine over and verified cam gears line up. I'm lost and struggling to get to work each day.. the dang cars only got 70k I don't get it.

[avguy]

.... I'm lost and struggling to get to work each day.. the dang cars only got 70k I don't get it.

Hats off to you for staying with this and trying to diagnose, because this one is a huge head scratcher. Usually when it gets much better and then immediately much worse again like this, it's something simple like a connector coming loose. One of the things I had eliminated with that temporary performance improvement was an internal engine problem. But this is so weird that I'm starting to reach for far out things like 2 separate problems. So what I suggest at this point is a compression test if you can get a tester, in order to make sure this is not an engine problem.

One other thing that comes to mind is the quality of the spark possibly not being strong enough. Did you ever ground the plugs to the block, in order to check the spark that way? If not, it might be helpful to do that, in order to find out what color the spark is.

Hope you can hang in there, because there's an answer somewhere. You've got a tiger by the tail there for sure.

[Chrisj4269]

That is one thing I forgot to mention, I did perform both fuel and compression tests last week. I want to say that compression was right around 150 but can't remember for certain. It was within the normal range and only varied about 3psi among all cylinders. I did the ground to block spark test which is where I thought two of the cylinders seemed slightly weaker than the other two. With it just being a visual test though it is possible they were all similar. The spark was blueish white. I feel like I should probably try that test again after dark though as it was middle of the day the first time. I just booked a rental car for another week but this may have to be the last week as it's almost to a point where buying a new car is a smarter choice vs continuing to dump money into the aveo and a rental... Thank you for all your help and let me know if you can think of absolutely anything else.

[Chrisj4269]

It may be worth mentioning, right after start the engine sounds fine and drops to normal sounding idle but after about 10 seconds it goes south quickly. Whatever happens in those first 10 seconds though seems to helping it operate normally.

[avguy]

It may be worth mentioning, right after start the engine sounds fine and drops to normal sounding idle but after about 10 seconds it goes south quickly. Whatever happens in those first 10 seconds though seems to helping it operate normally.

Just about every time I think of another possibility, that temporary performance improvement keeps telling me it's not the one. That said, I think 10 seconds is about all it takes the ECM to go into closed loop and start doing fuel management based on the sensors. So something like a badly wacked out upstream O2 sensor could make it run as you've described. And a simple test for that would be to disconnect the upstream O2 sensor connector, and then start it up and run it that way, which will force it to continue to run in open loop. The CEL will of course come on immediately due to the disconnected sensor.