[shorod]

If the the valve cover gaskets were leaking, and the plug well seals were letting oil into the plug wells, the dealer did not perform work that was not needed. Unfortunately, it would appear that is not the only issue the car has.

Have you used fuel injector cleaner in the fuel tank on a regular basis? If not, get a bottle of fuel injector cleaner and add it to the tank. Drive the car for 100 miles or so and see if that helps. I suggest adding 1 bottle at each oil change. I've seen it solve some pretty wild engine "problems." I can only imagine how many issues are prevented by using it regularly!

Does the idle issue only show up with the A/C on? Does the car idle fine with the A/C off? If so, I would start by checking the Idle Air Control (IAC) motor. The IAC is supposed to open with the A/C on or when other items put an increased load on the engine. If it is not functioning properly, it could cause idle issues.

Also, inspect all vacuum lines and hoses. Make sure they are all connected and in good shape. Others on this forum have discussed issues with the PCV vacuum hose cracking. Search the forum for details and check for the issue on your car.

Another potential problem could be a malfunctioning Exhaust Gas Recirculation (EGR) system. The EGR valve should close completely when the car is at idle. If not, it can cause issues such as you describe, or even cause the engine to stall. It's not that uncommon for the EGR pintle seat to become contaminated and not allow the pintle valve to close completely. If this is the case, one can often use a good throttle body cleaner to clean the deposits from the EGR valve and passages.

If you have access to a scan tool with a datastream function, that could greatly aid your diagnostic search. Monitor the air fuel ratio on the two exhaust banks and see if they appear to be affected by the stumble. If so, do they tend to go rich or lean? Rich and you probably have either a spark or vacuum issue. Lean and the problem may be in the fuel system (filter, pump, or injector).

With the scan tool, you could also monitor the coolant temperature and see if it seems realistic. With a warmed up engine, you can expect the coolant temp to be somewhere around 200 degrees F. If significantly different, you may have a bad thermostat or coolant temperature sensor. Out of spec coolant temp readings would cause the Powertrain Control Module (PCM) to alter the air fuel ratio to a less than ideal ratio.

-Rod