Chevrolet Repair: High Idle, manifold gaskets, chevy impala

Question
I have a 2000 Chevy Impala v-6; 3.4  Very high miles on the engine (312,000) but it still runs great. I have a very high idle when the engine is first started in the morning and only when the temperature is cold (usually below 55 degrees). Once the engine gets warm, I can turn off the engine and turn it back on, and the idle is fine.
I have replaced the idle air valve with no luck. Any other suggestions?

Answer
Hello Bob, I haven't seen or heard of this problem on this engine before. I have seen it on the DOHC 3.4 engine, it was the intake manifold gaskets. I guess it could be the intake on this 3.4 too. What happens is the rubber gasket doesn't seal between the intake and cylinder head and allows air to be sucked in from the crank case or outside the engine.  Try this, disconnect the idle air motor when the engine is running and leave it that way until the after you start it in the morning. If the idle is high then I would replace the intake manifold gaskets, The valve can't control the idle and when you disconnect it while it was running it will stay at that setting(idle).

Let me know what happens  


Mark