My motor surges up and down at idle (500-700 rpm). I have looked at all the vacuum hoses and they look ok. What else might be causing this? I know more about my V-8 car than this 2.0 stock fuel injected motor. Thanks for any suggestions.

timing is off so the idle air bypass is wrong to compensate AND the idle mix adj on teh ecu is lean

Cracked plenum-look around the 2 "holes" that are hollow studs that pass through the middle of plenum. Take off factory air cleaner. Get a propane tank and hook a hose to the valve. With the engine running spray a little propane gas in around the intake parts. Propane kills the engine. You may want to get a "fresh air" hose to the air intake so the motor get good air.

Unplug and block off all vacuum lines to the plenum except the MPS.
Block off the advance and retard ports on the throttle body also.

After that...does it still do it?

Rich