I take it this engine is EFI? I would double check that you got good fuel and fire - could be anything from a weak sparkplug wire, to a bad spot on the distributor, to a bad injector. I\'d check the easy stuff first - air filter, fuel filter, check for good spark on all cylinders. Might have to clean the throttle body and or clean the intake plenum (has a reputation to get caked with blow by and varnish). Check that all vacuum hoses are there and in good shape - a bad EGR valve, bad/cracked vacuum hose, bad/cracked hose to PCV valve, or clogged PCV valve can all cause idle issues. Make sure that you are not sucking in air anywhere along the intake manifold and around the throttle body - might try hitting those with some spray (some mechanics like carb cleaner, others use WD-40, some use plain water) - if there is a leak, the liquid will temporarily seal the leak and the idle will dramatically improve.