97 cavalier no start/high rpm/engine stall

thanks for taking your time.

On 97 cavalier 2.2 there are following problems:
- Engine stalls or studders on stop lights when i stop and idle. Not
every time though. giving  a little tap or two on a gas pedal would
stabilize the engine. some times i have to keep taping till the green
light.

- Couldn't start the engine after being parked for 3-4 days. I
checked
wires, plugs, spark was there. exhaust smelled like unburned petrol.
So, ignition is ok, fuel is delivered and yet it doesn't start.
Compression shouldn't be a problem, i replaced head gasket and valve
rubber thingies about 8 months ago and  compression was very good
after repair (9.6-9.8 not too bad for 140k chevy engine). Completely
puzzled i tried to start again. after so many tries it finaly
started,
very painfully, shaking, working erraticaly like it is completely out
of timing.  check engine was blinking.
i shut it down. then start it again. it was a OK. check engine is on.
messages P0300 and P0108.
- with engine warm (i haven't tried it on cold) i rev'ed it up to
approx. 4.5K rpm (in neutral) and could hear some missing. like the
engine shuts off for half a second. it felt like if i rev it up any
higher it would backfire.


i appreciate your response and thoughts.