93 Stocker won't Idle

[wuzfast]

My old '93 suddenly won't idle. It's not hot rodded at all, just my work mule and has been a real good one for 250,000 miles. It still gets good mileage and runs great too, it just quit idling. I can keep it running if I keep my foot on it but it will shake and die if I let it go below 1000 rpm. It's old, so I decided to put a fresh fuel pressure reg. and throttle position sensor on it today and it has a new DIS module on it that is only a couple of weeks old. Also the Idle valve has been changed but made no difference. Still won't idle on it's own. Broken wire in the harness maybe? It happened all of a sudden. While I was shifting between 2nd & 3rd and it almost died before I could get it in thew next gear. The RPM dropped like you cut the key off. It's a little awkward having to heel & toe through traffic so I just ran the idle stop up some to hold it at about 1200 rpm. Any ideas, I've already changed everything I can think of with no luck!

 

[Jacob07]

Just some generic things to try -

Check the vacuum

PCV Valve

 

[wuzfast]

Checked and found no vacuum leaks. With the car running on the throttle @ about 2000 RPM, I unplugged the throttle position sensor and there was no change. So I also unplugged the idle air bypass (which probably didn't matter anyway at that idle speed) and still no change. Shouldn't that kill the engine to unplug the TPS while it's running? This leads me to believe that there is a broken wire somewhere or some portion of the computer crapped out. It happened so fast when it went bad... like a disconnect.

 

[freakintiger]

Have you changed your IAC (Idle Air Control) motor? It regulates incoming air during idle and is the cylinder attached to your throttle body...

 

[wuzfast]

Yep! All new: Idle air control, DIS module, Throttle position sensor, Fuel pressure regulator, In-hose Temperature sensor. EGR and Throttle body nice and clean too.
The relay box has been fixed up with new relays. The Oxygen sensor is only a little over a year old. Maybe it wants a paint job or a vacation! I'm about out of things to replace except for the computer in the kick panel or a bad harness. I guess it's time to take it to a shop with a computer whizz guy and just hand him my wallet. I really can't bitch too much, it's got 250,000 miles on it and this is the first time it has stumped me with a problem I couldn't fix.

 

[freakintiger]

Fuel filter? Air filter? Have you tried a Base Idle Reset?

 

[wuzfast]

I"ve had the Batt. disconnected since Sunday and decided to put on a fresh Pos. cable since it was looking a little old at the Battery post. Not really ugly, just a little grey and thin. Put a new cable on and reset the throttle stop back to normal and fired it up to see if it would at least run good enough to get me to a repair shop. Well it not only started up and came back to a normal idle, but ran just fine today for about a 20 mile round trip. What the Heck ??? Could a poor battery connection have caused all that grief. I'll have to drive it some more and see what happens. I can't believe it just healed itself after being unplugged from the battery for a couple of days! There has to be more to it than that.

 

[16vstang]

If you dont start the car after a couple days does the battery go down, enough to need a charge or boost? Could there be a short somwere causeing the problem? Or mabe its just old and a bit on the tempremental side

 

[RustBucket]

You inadvertently fixed the problem (probably while you were pulling your hair out )

Disconnecting the battery reset the computer. It needed that with the new IAC, and TPS. You more than likely had a bad IAC, but after replacing it, didn't reset the computer, and the computer was operating the new IAC in the same manner as the old one. After the reset, the computer had to re-learn everything, and is now happy with the new IAC and TPS.