I have a 94 Bronco 5.8L. When i first start it it will unpredictably jump from 1200 RPMs and then drop and almost stall round 400RPMs. It doesnt stall and wont even out until the engine is hot. Once the truck is in drive when i push the gas pedal it hesitates. and wont go above 800 RPMs unless i floor the accelerator then RPMs spike to round 2500-3000. Even if i hold consistent pressure on the pedal the RPMs are again unpredictable and inconsistent.

I do not have an engine light on. My personal best diagnostic is the throttle position sensor. I am trying to find the best way to test this.

Also, if anyone has any other ideas as to what the problem could be please let me know??

Thanks in advance for any help or ideas!!!

 

Get a multimeter(analog is better but necessary), set it to ohms and measure the TPS, the resistance should change smoothly from open to closed with no glitches or dead spots. If you find any dead spots change it.

 

Pull the codes anyway, even if the light isn't on.

 

I would suggest fuel pressure issue, either pump or filter or regulator.

 

Start with the simple stuff. It's possible that the throttle plates are sticking. I just had that problem with mine. A few good squirts of throttle body cleaner cured it. Spray the llinkage on top of the throttle body, then remove the two intake hoses at the throttle body and spray the cleaner into them with the engine running until they are as clean as you can get them, usually a few good squirts into each bore will do it. If this has never been done and the TB is especially dirty you may need to take it apart to get it clean enough. I've done mine at regular intervals and have never needed to take it apart. It idles like an old Cadillac V8, in other words you can't even feel the motor running at idle.

 

I'd start with checking for codes (they can exist without the light). Guessing can get you in trouble in a hurry. All you need is a paper clip (not joking).

 

Ditto to everyone's suggestion ot pull codes regardless of whether you have a CEL on or not. Some codes don't trigger the CEL til the problem has occurred 40 TIMES!

 

www.fordfuelinjection.com has diagnostic info and instructions for pulling codes using a paperclip like mentioned above.

 

My 1990 F250 did something similar recently, leaving me stranded on the side of I-5. A guy stopped by, asked the symptoms, and immediately said it was the throttle position sensor. On my 460, it sits right on top of the motor, on the side of the butterfly valve housing. Two phillips head screws, disconnect the wires. I found a replacement, plugged it in, and it hasn't hiccupped since. Cost was about $60.

 

Those symptoms are "generally" the kind you will experience with a TPS problem but its still a good idea to pull codes first. If the TPS hadn't been the problem or there is more than one issue, your $60. could end up being twice that or more. Pulling the codes doesn't cost anything and gives you REAL answers bfore spending the money.

 

Roger that. I didn't have much choice, given my situation (no tools, much less a code reader).

 

For your truck you don't need a code reader: http://fordfuelinjection.com/?p=13

You just need a paperclip or short length of wire, some concentration and pencil and paper. I had everything except the concentration so I bought an Actron ODB1 reader instead ... hey look, a squirrel!