Join Date: Jun 2010
Location: United Kingdom
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Could be the EGR valve, can't explain how it will be open and then closed when warmed up but it's easy to check, if it were constantly bleeding air the engine would hesitate though.
Blank the vac pipes to the modulator just in case that's faulty and check the pipe from the modulator to the EGR valve too.
Is the PCV valve and pipe to the inlet manifold ok?
Sounds like an air leak, you'll need to isolate as many of the connections to the manifold as you can, brake booster, the 'other' vac pipe adjacent to the MAP sensor pipe (runs real bad without a MAP connected), not sure if you have a vac pipe from 'E' port on TB to charcoal canister, it goes via a valve that opens when engine warmed up. Throttle position sensor maybe?
last resort remove and clean the IAC, good luck.