94 Idle Problems

I have a 94 Bronco, 302 engine with about 140,000 miles; K&N air filter, true dual exhaust without a catalytic converter. I am having idle problems. When I start the engine and let off the accelerator, it will idle down to around 500 rpm or lower then idle back up, then idle down, up and down, and finally it will level out. If I put it in gear too soon, it will die. Sometimes when I pull up to a stop light the idle will maintain around 2000rpm or higher for a bit before idling down. This is driving me nuts!!! The other day I accelerated out of a parking lot and when I let off the gas the engine died. Does anyone know where the problem might lie???

Fuel or fire.

Mine did that, but it never died. It was a leaking gasket behind the IAC valve

OK... I started my truck this morning and it started, immediately died, and now won't start. :disappoin I am thinking the fuel pump bit the dust... Could this have been my problem all along?????

OK... I started my truck this morning and it started, immediately died, and now won't start. :disappoin I am thinking the fuel pump bit the dust... Could this have been my problem all along?????

OK... Got the fuel pump changed, added a new filter while I was at it. The truck starts now but it didn't solve the idle problems...:banghead:

OK... Got the fuel pump changed, added a new filter while I was at it. The truck starts now but it didn't solve the idle problems...:banghead:
It was getting continually worse to the point where it would often die as soon as I let off the accelerator while driving (not cool). Changing the TPI sensor didn't fix it... (Bad design. Had to remove the throttle body to change it out. Might have been able to do it without pulling the throttle body if I had a right angle screw driver). Fiddled with the idle adjustment a bit and have it to where it doesn't die, but still wants to idle up and down a bit. At least it doesn't die at every stop sign now... Will try the IAC valve next and update with the results...

try the IAC and clean the throttle body too when you have it off.

It was getting continually worse to the point where it would often die as soon as I let off the accelerator while driving (not cool). Changing the TPI sensor didn't fix it... (Bad design. Had to remove the throttle body to change it out. Might have been able to do it without pulling the throttle body if I had a right angle screw driver). Fiddled with the idle adjustment a bit and have it to where it doesn't die, but still wants to idle up and down a bit. At least it doesn't die at every stop sign now... Will try the IAC valve next and update with the results...

Mine did that. You just need a new throttle position sensor and you're golden.

Before you start pulling stuff take some carb cleaner and spray along the intake manifold throttle body if it smooths out the idle fix the vacuum leak.
Check for cracks in vacuum hoses and pinch off the vacuum line to the vacuum booster and see if this will help. Try this beforecleaning the throttle body as they charge a big price for a gasket kit.

I know this thread is getting old, but before anyone else decides to change their idle by adjusting that little screw. Don't do it without a volt meter. If the screw didn't cause the problem, it won't fix it. All you will get is serging idle. Find the problem with the idle. It can be a vacuum leak, IAC, Temp sensor, or many other things. You don't know how many vehicles I've had to spend hours diagnosing because someone adjusted that little screw. Not only will you have your origianal problem, but you will have new ones too. Unless you wan't to throw parts at your truck(buy parts until you get the right one), have your fuel injected truck or other fuel injected vehicle checked out by someone with the propper equipment to various sensors, etc..There are ways to check sensors and such with a multimeter, You just have to know the parimeters that your sensors are supposed to be at..You first have to have an understanding of how the components of fuel injection work together.
Im not trying to be an ass by no means. I've just seen so many people do this stuff. All it does is make it harder for your mechanic to diagnose the problems. So please, If you are trying to diagnose your truck. Please ask a good mechanic to verify what you are doing is correct. And be careful of people replying to threads on here. Many people that reply to post on here know what they are talking about.. And some don't. Just be aware..