conflicting diagnostic results

[TJB]

Hi, I'm trying to get a handle on some issues I'm having. I bought a 2011 Aveo six months ago to replace a 14 year old Saturn. For the most part the Aveo has been running great until today.

I had noticed that the Aveo sometimes struggled at 55mph. Nothing major, I would notice the tach would hesitate a little before kicking into gear. As long as I kept my foot on the gas, it would soon kick in and before I knew it I'd be doing 75. Also, it would sometimes stutter a little when I was in a stop and go situation. But once it got going, no complaints. I figured it might just be a result of my getting used to something quite a bit different from the car is been driving for the last 11 years.

This morning I took it to Jiffy Lube for a regular oil change and when I left, the check engine light was on. Naturally, I turned around and went right back to JL. They ran a diagnostic and said there were no codes. They ran it a second time and said it had something to do with my heat and asked if the heater had been running okay. Well, it's been 90 degrees for the past week so I can't really say how the heater is running. They couldn't dig any deeper without possibly voiding my warranty, but they assured me it would be okay until I got it checked our at the dealership.

I left and when I got a mile or two away I stopped for a light and it began to stutter and almost stall. I pulled into a parking lot and put it in park but left it running. A few minutes later I drove it around the lot with no problem. I went another couple of miles with no problem then stopped for gas. I left the gas station and stopped for a light. The stuttering started again and I barely made it through the intersection. Tach barely made it over 1rpm and I never got over 5mph in the three blocks I had to go to get home. When I put it into park I thought it was going to stall before I could get the ignition turned off.

I immediately called the owner at JL, who has worked on my cars for the past 15 years or so. He came out to the house and ran another diagnostic. This time he told me it was an O2 sensor problem. He took it out for a test drive and it ran like it was brand new-didn't stutter once.

Now I don't know what to think. Not sure if I've got an O2 problem or a transmission problem or what. I still find it suspect that it all got worse after the oil change, but can't prove that they did anything wrong. I'm taking it back to the dealer next week but at this point I don't know what to tell them to check. Any suggestions? Anybody have any similar problems?

Sorry this is so long. Any input would be greatly appreciated.

TJ

[thankful_ragamuffin]

A poor running engine will create shifting issues in an automatic transmission. When cars come into the shop with a CEL lit after a visit to a quick lube, we often find the intake tract has been reassembled incorrectly by the oil change artist after he checks the air filter. If the JL uses a cheap scan tool, the findings are suspect. The scan tools at our shop cost thousands of dollars up front and require a similar expenditure every 4 to 6 months. Check to ensure that the "oil change artist" seated the air filter correctly after he checked it and didn't allow debris to get on you mass airflow sensor (or unseat it). If all is good, find an competent independent shop to scan your car. The average GM dealership does not seem to understand these cars.

[TJB]

Thanks for the info. The problem has evolved since my first post. The next day I drove it 20 miles or so-half on a 2 lane highway at 65 mph, half in town through several sets of lights. It ran great and I started to think the stalling was a fluke. It sat for about 2 hours then when I headed for home I got half a block before it stuttered and stalled. Pulled into a parking lot, started it back up, let it idle, revved the engine, drove around the lot and it was fine. Pulled onto the road, went half a block and it happened again. Called a friend to come look at it and he couldn't find anything loose or out of place. Decided to drive half a mile to an auto parts store for another diagnostic. It made it the half mile with no issues at all. Had them run a diagnostic and got the same result-no code, followed by more research and the answer of HO2 sensor.

While we were there, we got talking to a guy with a shop about 5 miles away. He said he'd seen similar problems where there was sludge built up. He offered to take a look. In the five mile drive there, the car stalled six times, and revved a few times (a new symptom). When we got there, he looked at the air intake, then called chevy because he thought it was the O2 sensor. Chevy sent a tow truck to take it to the local dealership. It was 5:00 on Sunday, so the car sat there overnight.

Talked to the dealership on Monday and they ran a diagnostic and got no code, took it for a test drive and it ran fine. He thought that there might have been a loose valve gasket and that oil may have gotten inside so they did a fuel and exhaust system cleaning. They also found an updated program for cold start acceleration issue. They did a couple of test drives afterwards and it still didn't stall. I drove it home from there and 65 miles round trip to work today and it's running fine.

My concern now is I've read about similar issues on the consumer affairs website and it seems to be a transient problem with no known cause. I'm a little worried about it stalling out on me on the highway, I drive through a couple of construction zone where there is no shoulder to speak of.

My question to the forum now is what, if anything, does anybody know about this program update they did? Also, what are the odds that the cleaning fixed my problem?

Any help would be greatly appreciated.

TJ

[avguy]

I'd like to offer up a positive outlook for you, but frankly I think they're throwing darts. And unless there are way more miles on this Aveo than the 50K or so that it would be expected to have, IMO it's way too early for it to be having performance problems due to sludge or anything else along those lines. That oil change episode at the Iffy Lube is really weird, but it's hard to imagine what they could have done to ramp up the lesser problem you were having. There are unfortunately lots of things that could cause something like this. Did anyone check the fuel pressure at the rail? One thing that might help diagnose this problem is a real time scanner which can capture the data stream at the point of the stall in freeze frame. Perhaps you can borrow one from someone you know. Sorry to say that I think the will be coming back soon (but I hope I'm wrong about that).