'05 Aveo Losing Power, Bucking, and Intermittent Stalling. No codes, hard to diagnose

I have a 2005 Aveo, SVM Manual transmission 179K miles. For about 2-3 months now I've been trying to nail down a pretty big issue that I've been having. Sometimes while driving, the car will suddenly lose power and/or stall out. It will drop RPM's, start bucking pretty violently, and slow down sometimes almost to a crawl. If I let off the gas it will completely stall, but if I keep on the pedal it will eventually recover only to stall out once in neutral or making a complete stop. Recently it seems to mostly happen once I let off the gas and cruise to a stop. When it's having issues it will drop down to very low RPMs at a stop, almost as low as 100, for a few seconds then either stall or jump back up to 800-1k.

I will go a few days with no problems, and then one day it will happen over 10 times on my commute.

The oil pressure light seems to usually be the first light to light up when it stalls. CEL hasn't turned on, but checked to make sure no codes were thrown and none were logged. I've rented a fuel pressure tester and drove it around for a while but didn't notice any drops in pressure, but it didn't ever stall when I had the pressure tester hooked up to it. Perhaps I'll rent one again and hold onto it for longer and see if I can get it to stall while I have it hooked up.

One day it wouldn't start, there was no spark, checked the Crank Position Sensor (Which was replaced a year prior) and found a green corroded pin on the plug. Sprayed it with WD40 and it fired right back up. I replaced that and it seems to have gotten a bit better, but if anything the frequency of the issues has just gotten less. Also replaced the oil pressure sensor and the fuel pump relay.

I've read in similar threads it could possibly be the downstream O2 sensor, but I don't want to keep throwing parts at it in hopes of a resolution.

This forum has been a giant help in the past, If anyone has any troubleshooting suggestions I would love to hear from you. The car is dangerous to drive, and I would hate to get a new car for a silly little problem like this. This community has been awesome, I hope someone can help shed some light on my problem.

1) I would check vacuum leak first.
2) I would replace the fuel filter ( if it's there I don't remember one)
3) I would replace your injectors next

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Originally Posted by xintersecty

1) I would check vacuum leak first.
2) I would replace the fuel filter ( if it's there I don't remember one)
3) I would replace your injectors next

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Thanks for the reply. I've checked for a vacuum leak (Spraying hoses with carb cleaner) and the fuel filter is built into the pump. My thought on the fuel filter though, wouldn't a clogged filter cause a more consistent problem? And a consistent drop in pressure?

A friend mentioned the throttle position sensor. The 05' SVM is a cable driven throttle so the sensor is serviceable, I thought about giving that a shot this weekend. Im hesitant to replace the pump cause its $300+, and the injectors are pretty pricey too. Cant keep throwing money at this :(

A cable actuated Throttle Body should be more reliable than the fly by wire one. I would check the throttle body position sensor as suggested by your friend. It could be a bad connector.

I'll give it a shot and let you know what I find. I edited my above post, but I meant that my throttle was cable driven, not wire driven. Thanks!

When was the last time you replaced the plugs and wires. Also sounds like it could be a bad coilpack.

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Originally Posted by slayerized6

When was the last time you replaced the plugs and wires. Also sounds like it could be a bad coilpack.

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About a year and a half, maybe two years ago max. Had oil in the plug wells so I replaced the valve cover gasket, plugs and wires. I tried misting the coil pack/wires at night and didn't see any fireworks, not sure if a coil pack would go bad and not show sparks?

Welp.. replaced the throttle position sensor and it's still been stalling out, losing power, and dropping RPM. I got a fuel pressure gauge on it and have been driving around with it and recorded the following video:

https://www.youtube.com/watch?v=Eqaq...ature=youtu.be

This is just slowing down from foot on the gas to a stop. Looks like it's fluctuating about 10 PSI. I haven't had it stall out/lose power on me yet when I've had it hooked up to the pressure tester, but will update if I can get it to happen.

Does anyone have any idea if this is an acceptable PSI fluctuation, or does this alone point to the fuel pump/system as the culprit?

That was a scream. Next time you record a diagnostic video dump the tunes. Not that I don't mind a rocking tune, it's just gives us a chance to hear the engine.

Fuel pressure should be reasonably steady throughout the RPM range. Meaning at idle it should keep the system to the same pressure. There will be some fluctuation due to demand. So at idle you will see the needle bounce but a lot less than at speed.

So you're saying when you have the pressure gauge on your fuel rail, it works better? Maybe your leaking out the test port.

Ahh, my bad on the radio. Will definitely keep that in mind next time (Hopefully there's not a next time :) ). I didn't mean that it was running better with the fuel pressure gauge on the fuel rail, just that I hadn't gotten a chance to see if pressure dropped when I lost power/stalled. It finally happened a few times yesterday with the gauge hooked up, and the pressure didn't drop at all. So it seems like the fuel system probably isn't the culprit.

With that being said, the symptoms have been much better ever since I replaced the crank position sensor. They've decreased in severity and frequency. I'm thinking it must be something electrical. Maybe the connector for the Crank Position Sensor is corroded, or there's another connecter somewhere along the line that is corroded.

Aside from the crank or cam position sensor, are there any other sensors that would cause the engine to cut-off or lose power that I should be checking to see if I find any corrosion?