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Chevy Aveo, odd problem after odd problem

I have a 2007 Chevy Aveo. It’s at 148 000km. Never had an issue with it until 2 weeks ago. Started on a highway trip. Had problems accelerating after coming to a stop after driving higher speeds. Would stutter backing up. They changed the gas pedal assembly, said the sensor in it was shot. Also did a tranny flush. However when I took it back home a new problem arose. When i had to slow down to around 80 kms an from 110kms and hr but not completly stop(ie. In preperation for a light that may change or someone turning off the highway) it would hesitate. I then changed the spark plugs. It then seemed to run ok for 2 days. I them had the timing belt changed, just strictly since it was due for maitenence at 100kms. But, when i got the car back it seemed to have a rough idle when coming to stop in town at a stop light or sign. But it did not affect the RPM and did not hesitate to go when accelerating. We then put a bottle of fuel injector through the tank hoping it was maybe dirty injectors. Also changed the spark wires at this point. After about 3 days, the check engine light was finally throwing a code. It was the map sensor. Changed that. Car did run good for about a day. Then went back to idling rough. But once again, not affecting the RPM or acceleration. Was still hoping the injectors. Took it out for a hr and half highway drive to get the tank of fuel with the injector cleaner ran through it. Ran fine the way there. Went through that tank of fuel. Filled again. But on the way back i had stopped for supper. Went in and ate then went to back out of the parking lot and the car sputtered the whole way backing up, and then kind of chugged a bit till i was acellerated to about 20kms. Since then have had no issues backing up or accelerarting and back to just rough idles at stops, but not affecting the rpm or accelerating. The only other thing that was done was put a bottle of irontite into it try to seal up some leaky valves. At a loss of what else to change. And no longer throwing and codes since i changed the map sensor. Any ideas of what to try next?

I was thinking fuel filter until you wrote “leaking valves”??

Irontite chemical products are block or radiator sealers. Do you think the engine valves are leaking or is this a cooling system leak?

You are aware that you have essentially reached the design life of this car, right? The Aveo does not have a good reputation for reliability or longevity. If your engine valves are leaking, this thing isn’t likely worth a valve job.

You were playing with fire to go 148,000 kms on a 100,000 timing belt.

It sort of sounds like there’s more than one problem. If I had this problem on my car, if it was about time for any of these according to the maintenance schedule, and nothing was wrong by a simple visual inspection, the first thing I’d do is check the battery and alternator, replace the engine air filter, fuel filter, spark plugs, distributor cap, spark plug wires, ignition rotor, and measure the fuel pressure and ignition timing. I’d also measure intake manifold vacuum at idle and check for vacuum leaks. I know all that sounds like a lot of work but on my Corolla it would take about 3 or 4 hours is all. Less time I expect for a pro with experience on this make/model.

If it still wasn’t running correctly, next up I’d check compression and valve clearances if applicable. Still not running correctly? Cat back pressure test.

Edit: Has a fuel mixture test been done? The tech needs a real time scan tool to do that. If they have one, ask to have a “fuel trim” test, it measures if there’s a need for the engine computer to inject more or less gasoline than it thinks it should. Something faulty in the mixture system could throw a code for the MAP when in fact the MAP was ok.

I have an idea of what to try next. Bring it to a reputable repair shop and have the problem(s) diagnosed properly.

I’d start with a compression test and put a vacuum meter on it. That would give you a good snapshot of how evenly the engine’s cylinders are operating and disclose any system vacuum leaks. The vacuum tests would also disclose problems with sticky valves or valve timing. Sticky valves can easily cause erratic operation.

George made a good suggestion for the real time scan tool. That means the engine’s critical operating sensors are monitored as the engine is run, showing up erratic behaviors such as erratic injector operation.

A good diagnostician can get to the bottom of this. And you’ll then know whether or not it’s economically repairable. Keep in touch. We do care.

When I took it into the repair shop 2 weeks ago they did a complete diagnostic and the only things they could find was the gas pedal assembly. Also, they noticed the leaky engine valves. And yes, it has a cooling system leak. Has since i bought it at 60000 kms. Which was what the irontite was. Sorry, definitely didnt wrtie that right. But when we replaced the timing belt, we found there was a litttle leakage in the water pump, so that may have been the issue with that. The gentleman doing all the work on the side is not a mechanic for a living. He is retired. But, is definitely reputable. . However, I like to learn and am around and helping during the work. And I most definitely appreciate the suggestions you have all given. Will start looking into some of these. I do understand taking it to a shop, but I have put almost 1700 dollars into the car this month. I did only pay 3500 dollars for it 4 years ago. With the make of car, its coming down to whether or not to invest much more money in it. Its coming up on its lifespan, just has been such a great reliable car till now that I do want to do what I can to keep it running. Within reason of course, also remebering i did just drop that amount of money into now and dont want that to be wasted. Also am currently laid off in the terrible economy of AB, canada right now and am feeling terrible going to this gentleman who knows my situation and doesnt ask for much for his time. Just trying to speed up the pinpointing process. Was hoping this may have been a commin problem with the Aveo. Hes at the point of scratching his head as no codes ever show up when he has checked. Same with the shop diagnostic done 2 weeks ago. Thanks for all of your replies, will see if he has the tools at his garage to do those tests or take it back into a shop. I appreciate your time!

“The gentleman doing all the work on the side is not a mechanic for a living. He is retired. But, is definitely reputable.”

He may well be an honest man, but I think that–at this juncture–you should be questioning his competence. I know that you are trying to spend as little as possible, but I think it is time for you to take the car to a professional shop with a good reputation, and to have someone with more competence do the diagnosing of what could well be multiple problems.

"Also, they noticed the leaky engine valves"
Leaky engine valves affect compression, combustion, and the engine’s operation overall. They allow unwanted air w/oil to be drawn in past the valve stem seals on the intake stroke (I bet the seals are shot too), affect the cylinders’ abilities to compress the mix, and allow part of the explosion pressures that should all be pushing the pistons down to blow past the valves… burning/eroding them and making the problem worse. Leaky valves can cause all form of erratic engine operation all by themselves.

At this juncture, I think I’d get an estimate to get the valves redone and decide whether it’s worth the investment.

@Mustangman, th OP quoted mileage in kilometers. It’s less than 90,000 miles. I wonder if you were thinking the mileage is higher?

Concur w/ TSM , focus on the valve problem. Before most shops would remove the head and do a complete valve job they’d do a cylinder leak down test and check the valve clearances first.

No, @jtsanders, I saw it was km, not miles.

My niece had one of these cars. I worked on it a couple of times and checked forums before I did. Seriously problematic at fairly low miles - lower than we expect today. It was a 100,000 mile throw-away from what I could see. Built to be cheap, not durable.