I have a 93 Tbird with a 3.8L, Fuel injected (sometimes I think about getting rid of this car but have to hang on because of finances) that went wacky on me today. I drove to work fine and to my first appointment 20+ miles away fine-got out of the appointment and started the car and the idle shot to 2500 rpm and stayed there. I hit the gas to see if it might reset-no change. Turned it off and started again-no change. Got back to my office and every time I started it to go to my next stop-same thing. A mechanic friend said it might be my throttle air by-pass valve sticking. Do they go bad? There is a label on the outside of it that says "Do not clean inside throttle body or adjust throttle set screw..." Does anyone know or have any other suggestions as to possible causes I can fix or do I need to take it to a mechanic?

 

Yes, Idle Air Control valves do go bad. I can't remember the last time that I had 1 make the car idle way up.. Usually the symptom is the car (or truck) won't idle at all, or idles very low rpm..
Is the check engine light on now, or while it's running at high rpm?
Have you check for computer codes?
They do make a cleaner that is safe for throttle bodies.. Ford coated thiers and the average "carb cleaner" can eat the coating off, causing problems..
A fairly large vaccum leak can cause the same results, high idle/rpms..
How mechanically inclined are you? an IAC isn't hard to remove to inspect..1 connector and two 8mm headed bolts.

 

Yes, sometimes they do idle way up. I just recently was trying to solve an irratic idle problem on my 90 Beretta ( a new problem every week). When starting, the idle would shoot high, then slowly come down to normal. Then it would be iffy the rest of the trip. After checking several other things, I looked at the idle air valve. The metal pintle was gummed up with oil and dirt. After cleaning it off with a cleaner and toothbrush, and reinstalled, the idle problem went away. I'm guessing the goop would make the pintle stick, so the computer tried to over compensate, then the valve would pull free suddenly with a real high rev. Then the computer had to slowly try to bring it back down again. This happened over and over again.

 

I agree with argent, check your vacuum hoses for leaks. That's about the only thing I can think of that might cause high rpm idle. good luck and please let us know what the problem was

 

Thank you for the suggestions. In response-no check engine light. I have not yet had it hooked up to a computer. Two followup questions: I have removed the idle air bypass valve. It is dirty inside-should I attempt to clean or just replace? Second, any suggestions as to which vacuum hose may be the culprit? What is the best way to check-just get hooked up to the computer or start pulling off ends and plugging? Or spraying hoses with Fuel Injector cleaner?

 

I would replace it if it's not an expensive part, probably only 10-20 bucks. Then again, you can probably clean it and have it as good as new, so it's at your descretion. First off, remove one vacuum hose, check for cracks, worn ends etc. then put it bvack on and check another. If none of them show any cracks or problens, fire up the car and unplug one end and put ur finger over it to make sur it's actually sucking. If it's not you could have a bigger problem. Go ahead and clean up your throttle thing and stick it back on, then check for cracked vacuum hoses. I have a sneaking hunch that those might be the problems. keep us updated, joe will be online soon and he's the real expert.

 

The best way to find out if you have a vacuum leak without physically touching ALL of the vacuum lines is to get a vacuum pump. Connect it to any vacuum line (NOT DIRECTLY CONNECTED TO THE INTAKE!!)and see what the reading is. If it is less than 15inches then you possibly have a problem. If the rev is caused by a vacuum leak then you will be able to tell right away, because the vacuum gage will problaby read less than 10 inches. This is very effective and timely way to diagnose or dispell vacuum leaks. I know the major parts stores sell a plastic version of the MityVac tester for around $20. A very wise investment.
Good Luck,
Hope this helps,
Billy

 

On the assumption you don't have a scanner, I'd take the idle air control valve off, clean it as best you can, and put it back on. If the car runs normal, or better than what it did, then I'd go ahead and replace it..The suggestion by BelairBoy to clean the throttle body also is a good one. It doesn't require any special tools, doesn't take real long to do, and will help the car overall in the long run.

 

All posters are correct. Ford makes a special TB cleaner---get it, as mentioned, ordinary cleaners can ruin the TB.

IAC valves are common on Fords. Price depends on the source.

 

I just wanna put a big smile here cause I answered a question and a knowledgable person agreed with me, which shows Im learning. sorry this isnt helpful, but I'm doin good