I fixed the throttle body gasket, it was leaking bad, but the idle is still a little high. Before I had the truck, some shop tried to fix it by backing out the idle speed screw. Says the paperwork. The shaft doesn't even contact the screw. So something else is wrong.

The IAC appears to be working. Its relatively new, and vibrates with pins A and B jumped. I'm guessing that means its working.

Suggestions?

 

Coolant temperature sensor?

It sends signals to the computer to increase injector pulse width.

The sensor on the front of the engine next to the water neck.

 

Its pretty new looking. It seems someone worked on it before. The IAC appeared new too and they adjusted the idle screw, but failed to replace the base gasket.

Since I fixed the gasket the idle is inconsistent now. Sometimes it idles right, but when I hit the gas and let off, it comes back up a little too high.

Maybe I need to adjust the screw back to near factory setting and let the IAC do its job correctly?

 

I tested the coolant temp sensor and it was bad so I replaced it, no change.

Tested the TPS all good except the idle is a little high at .72 volts.

EGR is good.

Can't find any vacuum leaks. With the map sensor disconnected electrically the idle comes down just a little. If I disconnect the vac line it comes way down for 2 seconds then back up again.

If I use my finger to plug the IAC hole the idle comes down to where it should be.

How does the IAC get its input? TPS and MAP? Then the ecm sends out a voltage to regulate it? It has to read rpms right? I don't think the IAC is being regulated properly.