You might want to check the cooling system for pressure or do a compression/leakdown test.
Theis will telll you if there is a blown head gasket or other issues.
Check fuel pressure. Try running some high quality fuel system cleaner such as SEA FOAM or BG44K. You might have to go to a service station. Expect to pay $10-20 per can and run 2 cans. You willl need to change the oil afterwards as it works sos well the deposits it removes gets the oil dirty.
Ave you tuned it up? As in Spark Plugs, Plug Wires, etc? If so how long ago?
The intake and throttle body could be dirty, as well as the Idle Air Control Valve, (IACV), and the Fast Idle Thermo, (FIT). If the Intake tract and throttle body are dirty, that can affect performance. If they are dirty, the IACV, (which controls the idle as the engine load increases from; power steering, air conditioner, headlights, other accessories, etc. The FIT control the idle in sort of the same way, but it works when the motor is cold like a choke and it can fail which can affect the idle even after the motor is warmed up.
There are also emissions stuff like Exhaust gas return, Positive Crankcase Pressure, PCV Valve, etc. Which can have some affect but not as much as the other items.
Try the fuel cleaner and check tune up items as well as tests. Then get back to us.
Wednesday, September 14th, 2011 AT 11:33 PM