Iac problem?

[drcomanche]

So, I purchased a new IAC for the Comanche, but when installed, it idles at 3000 rpm off the bat. I looked at my old one and it seems to be stuck in the open(?) position, with the plunger sticking all the way out. With that one installed, it works ok. The idle stutters and sometimes idles at 900 and other times 600. It definitely misses a lot, but I'm not sure if that has to do with the IAC or the age of the vehicle. And it gets pretty terrible gas mileage, even for the tires.

 

Any ideas?

 

On a may be related side, the truck does backfire when shifting at mid to high rpm, and I still haven't been able to change my O2 sensor.

[cruiser54]

Plunger sticking out is closed positon.

 

Do you have tune up issues? IAC will not cause a miss.

[drcomanche]

I have replaced:

Spark plugs

Cap

Rotor

Ignition coil

injectors

Air filter

Fuel filter

Mass air sensor

Exhaust headers

 

And while I did the headers I cleaned all my ports and the intake manifold, including the channel for the IAC(not with it in, of course).

[cruiser54]

No new igniton wires?

 

Ever refreshed all your grounds or checked your sensor ground circuit with a meter?

[drcomanche]

sorry, forgot about the wires, but yes, they have been replaced, and I have sanded and made sure all my grounds have good contact points. At this point, after some research, I have vaguely heard that the new IAC requires a certain setup to "tune" it? I never hear about it, but maybe somebody on here knows how it works?

 

As for the rough idle and misses, I'm think MAP sensor or TPS.

[cruiser54]

No real need for the ECU to learn what the IAC is doing on a Renix.

[drcomanche]

It isn't a Renix engine, though. The Comanche may be an 88 but the entire drivetrain is 94 cherokee, including engine.