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Hello, all. 2009 Aveo LS
The venting noise is consistent and constant. The surge is somewhat constant/intermittent. The car has an idle that surges at fairly regular intervals when in park/neutral and less so when ECM is control. The rpm needle doesn't seem to drop. It just seems to have a periodic surge from normal idle (750?) to around 1000 RPM. There is a venting, air rushing or woosh / wooshing noise when it happens. It sounds like it dips down then revs up but the RPM gauge doesn't seem to reflect that. Kind of sounds as though the car is snoring. Vent noise, sometimes a surge, returns to idle for a moment and makes the venting noise again. Sounds almost like a shush or shh for 2-3 seconds the duration doesn't seem to vary and the cycle is about 7-10 seconds.
My guess is that something is malfunctioning when the vacuum or pressure somewhere reaches a certain level, but I can't tell. I can't tell if it's still happening with the accelerator in at higher RPMs. No engine light on, yet, but it's only been driven about 10 miles since this began. The dash lights don't dim when it makes the noise/surges.
Backstory for anyone curious or looking for troubleshooting stories in the future:
Our vehicle, and only vehicle, started hunting only at idle/neutral a while back and continually worsened to a rough idle over several days. Since there is no IAC and there were no other symptoms, I decided to remove the intake stuff, have my son step on the gas pedal, blasted it a few times with the TB cleaner and gently dabbed it with a cotton t-shirt. It had a ton of visible crud. It seemed, like it was instantly better. Additionally, it got rid of a major hesitation issue I never knew it had.
The problem came back, or a similar one appeared, but it was worse, so I threw in some NGK iridiums. The original plugs were still in there with a almost .55 gap. The new ones were factory gapped to just about the 2009 recall specs. The car didn't like that at all. Drove it a bit hoping the ECU just needed to adjust, but we later discovered it was having multiple random misfires. Seemed to point me to a faulty COP or faulty boots. I realized that I hadn't changed the air filter in 2+ years. I changed it and the problem seemed to be fixed.
It returned and I checked the VIN on the GM recall site to discover that our car was not included. I decided to make the assumption that it must have only been for some fives and/or some regular Aveos. I also read on the forums here that the replacement is a colder plug. So I decided to hedge my bet on the COP failing or just having to live with copper plugs and OEM specs. I gapped the ones I had initially removed with the intention of troubleshooting the coil and the misfires disappeared. It reduced the severity of the issue.
Then it got really bad. I was for sure it was a vacuum leak and had the wife start her up cold and I spritzed carb cleaner here and there. I also jiggled what I thought was the purge valve/solenoid and the intake manifold. She killed it when it scarily dipped below 500RPM. I drove it toward the auto parts store and it died at the stop light. It started surging at start up during the previous repair attempts. It nearly died a few more times until we found a store with an upstream oxygen sensor and replaced it due to the repeated codes and symptoms when we checked at the first store.
Changing the oxygen sensor made it drive-able again. We could slow roll into stop lights and idle as little as absolutely necessary, but we also got some lean codes. The oxygen sensor had well exceeded its life anyway. Then I cleaned the MAF with CRC MAF cleaner. We also used a hose, rubber glove, rubber bands and cigar to check for vacuum leaks. We couldn't find any. It was slightly rough, but after two 3 minute idles it was rock solid. Then my wife realized the new noise we were hearing was coming from the car and then it started surging when the noise would occur.
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