the great mystery problem

I have a 04 Aveo the original problem started about 6 months. nobody could find the problem.my friend bought the car new. when you drove the car it would lose power and stall very intermittently..the car would start right up and then run fine ,until the next time it stalled ,no time or pattern ,it varied .NO codes showing..he took it to 2 shops and the dealer. The list starts:complete tune up plugs wires, coil pack, throttle cleaning.etc they said they couldn't make it stall..so he read some forums and i helped him change the fuel pump and ran a couple cans of sea foam in the tank in case there was any water in the tank..didn't help ,then the catalytic convertor..no help ..he moved and i bought the car from him..so i cleaned the throttle body .installed a new EGR valve.motor still stalls,and NO CODES..next throttle postion sensor that did fix a very low idle..the car now not only stalls out it is running were bad with a intermittent missing. i was bound to figure this out .compression test cylinders were all even with in 1%or 2%..the motor broke the timing belt 16000 miles ago..so new head and belt..this year model did have a problem with failing valve springs that caused a miss.so that has been eliminated.so next the hose to the air box was torn so a replaced it with the cold air sensor and this helped the missing tremendously... the car did stall out more when it was hot .So finely i changed the computer..used.. this fixed the stall problem !!!Now check engine light is on.intermittent miss code..again new plugs ,wires ,valve cover gasket that was leaking,crank sensor,which fixed the missing. still have the code light .could it be the o2 sensor with no code? car runs great and gets 27 mpg around town.I used to be a professional mechanic, so with ego bruised please HELP!

with no codes to go on, internet diagnosis is harder. If there stalling occur while trying to return to idle, and you replaced the tps i would say do the idle relearn procedure, posted on this site a few times. See if that helps the idle issue.

For the missing, you are sure is it missing? as the miss would throw a code. Is it more of a hesitation? Describe how/what happens. It could be simple like a vacuum leak, to a stuck egr. Or you could have many possible issues.

What kind of plugs are you running, and how often do you change them? Have you misted the ignition system to check it for spark arcs? And is the car a manual/ automatic? does it do it with the ac on/off? etc.

The car doesn't stall any more .the new used junk yard computer fixed that .The car would stall out when it got very hot in heavy traffic around a steady 2800 rpms.i figured that the old computer some how was just over heating.the car is a Manuel trans.i read your post talking about how hot the coil is on these cars.so that is when i looked at the plugs.3 k on them they were iradium and they were destroyed.OEM showed copper plugs so that is what i installed.they had a little oil on the old plugs so i installed a new valve cover gasket and new bosch wires.the car doesn't miss from a roll 1500 in 2nd gear it pulls smooth to 6500.if any thing it my have a low range very small flutter between 1500 to 2800.I did check for vacuum leaks.This is a strange problem i was hoping somebody had this problem and know the answer.i how how hard it is to trouble shoot a car without seeing the car.Differently one of the things i hated about being a mechanic at parties people trying to tell you what was wrong with there cars,and wanting you to trouble shoot it for them by there sound affects .LOLThe car will not pass emission with a lite on,or i would just drive the car .it runs great .if you turn it off it just comes back on.

you finished with the light on? is it on or off? if its on what is the code?

that rpm range is constant in every gear? under load? i would check the variable runner intake system.

The light on is probably just the crankshaft positioning sensor that needs to be corrected. Dealer issue.

Well thanks ,ontarion frog,and petrified rabbet...Took the car to the dealer it took the tech a couple of tries,to make the light to go out..He did the crank sensor.relearning .but the light came back on a few miles down the road ..He wouldn't tell me exactly what he did, i told him there was a service bulletin on this problem,He told me that he had to use a different procedure..bUT it is fixed..