I read a thread on here about cleaning the throttle body. As I recall some of the symptoms you are describing were attributed to that needing done.

Prepare for minor blood if you try to do it yourself.

 

There are three possible things I can think of Andrey that might be causing the new symptoms.

1. As Grizzly suggested, a throttle body that might need cleaning.

2. An exhaust leak, especially at the flex joint behind the engine.

3. Contaminated fuel, either from the place where you buy it, or from condensation in the the fuel tank of your HHR.

 

thanks for the info.
1. I cleaned the throttle in August. Unfortunately, after cleaning i had problem with the software. Some with the engine speed. But the problem removed at once through the reprogramming of car's brain. I rule out the throttle.
2. I will inspect the exhaust system.
3. Problems with the fuel - it is very likely. A pair of *******s spend their policy so that the wholesale price of gasoline more than retail. It is unlikely that Americans will understand it immediately, or at least believe this - but it's true. Result, we have the gasoline's properties as donkey's urine. The worst thing you can not just switch supplier. All Russia has such gasoline or even worse.

 

sounds like the prolem i had, replaced the timing chain and all is well.

see my thread on p0016 code

 

I read it (incidentally, a good record).
But my "check engine" does not bother me (yet). At the same time, I was horrified to think about replacing the chain - is too high costs.

When we started this conversation ..
You replaced the chain. What else do you replace at one time with a chain? Chain tensioner? Some of the gaskets and O-rings?