intermittent loss of power with no code...help :(

I have a 2005 Aveo, 102,000km. I just had my head replaced after my idler grenaded. The car drove great for the first week but now I am losing power when I start to accelerate. It does it at about 10% throttle, if i give it more gas it starts to run normal. The problem is intermittent. Sometimes it does it when the car is cold, sometimes only when it warm and its always worst when i accelerate from a stop. if i am cruising down the highway and gently press the pedal i only feel slight hiccups.
Mechanic replaced the timing belt, pulleys, checked EGR wasn't stuck, replaced the TPS, compression test was perfect, fuel pressure test was perfect....anyone have a similar problem or any ideas?

It could be a number of things, and it's just speculation at this point. If this was a DIY you would dig into it, starting with a compression / leak down test, along with a check of the timing. But since you just spent a lot of $$ to have this repaired professionally, take it back to the same mechanic, who should absolutely stand behind his work. You paid to have the job done right.

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Originally Posted by avguy

But since you just spent a lot of $$ to have this repaired professionally, take it back to the same mechanic, who should absolutely stand behind his work. You paid to have the job done right.

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As a service manager at a Napa Autopro, if our shop had done this job it would absolutely be warrantee. Our warrantee policy is 1 year parts and 6 months labour standard, expandable to 1 year labour at no extra cost if you register with Napa. That is pretty much industry standard now.

My mechanic has gone over it twice and hasn't charged me a dime for every test he run since the head was replaced. He made a small adjustment to his timing but everything is perfect. He has got input from other professionals because he is stumped at this point. Another mechanic thinks it may be a transmission problem. Has anyone experienced a similar problem with loss of power when accelerating due to transmission? It's not giving us a code which is really frustrating.

I didn't pick up from your OP that the same mechanic has looked at it multiple times, so it's apparent that he's trying to hold up his end of the deal. A shade tree DIY guy like me would feel mighty uncomfortable making suggestions while looking over the shoulder of a professional mechanic, especially when he's already asked for help from other pros. I believe your current problem is somehow related to the original one or the repair, but that's just speculation on my part. About the only thing I can think of that's fairly obscure, and may be easy to miss is the small MAP sensor connector hose (which was handled during the repair). Others have posted that this hose became brittle, cracked slightly, resulting in hesitation without setting a code. But your problem could of course be 25 or so other things as well. Hope you find the answer soon, and please post back what the problem actually turned out to be.

I read that when the engine blows from the timing coming off that it can put some nasty stuff into my catalytic converter, so I went for a drive tonight on the highway and my car wont go past 100km/hr, it works hard like it wants to but just wont do it no matter what. I didn't get rough with it because I dont want more problems of course but if the back pressure is so high it wont let me get anymore power right? Also wouldn't I be getting a code?

Thanks everyone for their input by the way....really want my car back to normal! :)