Hey everyone,

I was wondering if there's a way to low the idle speed on my bronco. I got an '89 straight 6 with EFI. I was thinkin maybe a circuit to adjust the reference of the MAP sensor but that would only change the fuel ratio. I'm wonderin what I can do because it's idling at 1100RPMs. I've replaced all the intake manifold gaskets and I can't find a single vacuum leak so I don't think that's the problem. The O2 sensor is new, the TPS is new and the ECT is new as well. When I bought the truck over a year ago the idle was around 650-700RPM and that's where I'd like it to be now. Though, that was before the header and cam. But it would be nice to hear the thing lope at idle.

Thanks for the help.

 

Hmmm why don't you try the screw at the throttle body? maybe the idle was a little high because the engine was failing and someone adjusted it up to compensate. Try lowering it a little there and see what you find, maybe it will work just fine.

 

Oops, I forgot to mention that I had already tried that. Bringing the screw up didn't change a thing. The throttle plate had still stopped where the screw was before I adjusted it so there must be something else causing the high idle. I'm wonderin if it might be a bad sensor other than the few that I've replaced? I'm gonna check to see if it throws any codes when I ground the self test wire sometime later today to see if it can tell anything. I remember when I had replaced my intake manifold gasket that I had forgotten to replug in the map sensor and it idled exactly how I want it to idle but I know I can run it like that cause the computer didn't know what the hell was goin on with the air/fuel ratio cause it was runnin real rich. Well you guys got any other ideas?

Once again, thanks for the help.

 

The screw on the throttle body should NEVER be adjusted... it DOES NOT adjust idle at all! The ONLY idle control is through the ECM (computer)! Adjusting the screw on the throttle body will completely mess up fuel ratios and cause no end of difficulties. The screw in the throttle body is a STOP ONLY to keep the throttle plates from sticking in the bores. In short there IS NO IDLE ADJUSTMENT on the EFI (EEC-IV) trucks accept to make certain you have no vacuum leaks and all of your engine sensors are functioning properly.

I cannot stress enough how potentially destructive it can be to adjust the screw on the throttle body of theses trucks. You will defeat the IAC leaving the computer with NO way to control idle air supply which will cause a permanent lean condition that will ruin plugs and eat your fuel economy. If the screw has been run in and the throttle bores opened you will have to get the truck to normal operating temperature. Shut it off. Disconnect the IAC. Start the truck and IF the truck does not die within a second or two, you will have to back the screw on the throttle body out until the engine dies. Once it dies, turn it off, reconnect the IAC. Clear the fault codes that triggered because the IAC was disconnected. Restart the truck with the IAC disconnected. The truck should die within a few seconds. Assuming it does, shut the truck off again. Clear codes again. Reconnect the IAC. Open the throttle and check that the butterflies don't stick in the bores by letting them snap shut and trying to re-open the them. Assuming they don't stick, restart the truck. It should idle. You have successfully reset the throttle plate stop screw. DON'T adjust it again!