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Rough Idle

My 2001 Mercury Villager idles rough, but runs fine when driving. I replaced the plugs, wires, distributor cap, rotor and air filter. Then I took it to the shop and they said it had a code that indicated the #6 cylinder had misfired at some point and it required an intake manifold kit (O rings on the the injectors), but that failed to correct the problem too.

Idle speed is controlled by the Idle Air Control (IAC) valve. If the valve is dirty or sticking it can cause a rough idle.

Can the valve be cleaned or does it need to be replaced. How can I tell if it is sticking?

If sticky it can usually be cleaned - just blow it out with some carb or intake cleaner.

I would also check for routine vacuum leaks - rather than something extreme like the manifold gasket.

Did this shop have anything to say after they ran up a huge bill w/out fixing it? Did they happen to check the compression?

No, they didn’t give much information on what tests were performed. I am trying to get my facts together on the subject before I confront them about their poor service.

Thank you for the help!