Hey everybody, thanks for all the informative posts. I've been pouring through the forum for days for suggestions on the following problem. Learned a ton, but still no luck!!

94 Ranger 3.0 125K, standard. Every couple of days, the idle will get stuck revving really high in neutral, at seemingly whatever RPM the engine was running when I took it out of gear. Sometimes it'll keep idling high when it's in gear, to where I can cruise at 35 MPH in 3rd with no foot on the gas. Sometimes it even seems to increase RPM between gears. It idles down to normal RPM only when I come to a complete stop, sometimes not even then. All the time it's doing this, the gas pedal is in normal position, so I think the throttle is mechanically ok.
I cleaned the MAF, replaced O2 sensors, replaced air filter, replaced PCV, cleaned throttle body (dirty), cleaned IAC solenoid (filthy). I checked vacuum lines, inlet air temp vacuum motor, throttle movement for mechanical probs, put an ohmmeter on IAC and throttle position sensor, both read normally. I can't find any EGR system. Check engine light has only come on only two brief times out of doing this 20 or so times. Had the codes read at Autozone, no codes came up.
Is it possible that the IAC would fail intermittently? Any other ideas? Please help, I can't afford to replace all the wrong stuff!
Thanks.

 

Welcome to FTE!

No need to rely on AutoZone when you can pull codes from your '94 EEC-IV system by yourself, without a scanner:

www.smpcorp.com/download/view/Tt4Q98.PDF

I would start there, just to be sure.

Other than that, it sounds to me like you've pretty much checked everything! Have you been able to look and listen under the hood while someone inside the cab presses the gas pedal, and that kind of thing? Did you add any kind of lubrication to the mechanical parts when you checked them?

I honestly don't what else to tell you except that, if I were in your shoes and had eliminated all possible mechanical causes and ensured that there were no trouble codes stored, then I probably would be just about at the point where replacing the IAC would be my first course of action, and then replacing the TP sensor would come after that.

Maybe someone else has some other ideas...

 

Rockledge, thanks so much for the info-- that PDF you sent is great. I thought I had to have an analog voltmeter to test codes myself. All I need is a ground wire?!
I did have my wife press (or "mash" as some say down here in the South!) the gas pedal while I watched the throttle mechanisms move, they looked fine, although a couple of the springs did look weak. I'll spray some WD-40 around there to see if that helps anything. I'll test the codes, maybe change the TPS, then the IAC as you suggest and see what happens.
Thanks again, ford-trucks is a great site thanks to folks like you.

 

Well, I read the codes, KOEO got a 122, and KOER test yielded a 411 and 412.
I replaced the throttle position sensor, and the fast idle problem seems to have gone away... but now there's a horrible rhythmic hesitation at the low end in all gears, like a sputter in low RPMs. What's that all about??

 

Did a full tune up, now runs like a champ. I hadn't looked at the plugs, because my "trusted" garage told me a week earlier that the "tune up parts look fine". I assumed that this meant they pulled at least one plug out to look at it. Guess again! They were trashed due to an overheating I had last winter (pet-friendly coolant froze solid, cracked radiator, broke fan on water pump).
Now it runs fine.
For now.
Thanks!