this morning when I started my car the idle seemed high. I wrote it off to the cold weather. however when I drove to work I noticed the idle was much higher than usual. with my foot off the throttle the idle was high enough to keep me going about 40mph at 1100rpm. when I put it in park the rpms shot up to 2,000rpm. car drove fine. at first I thought it was probably the tps but now im thinking maybe a vacuum leak. what say you? if its a vacuum leak where are the most common areas to check? just around the throttle body?

 

spent about an hour on this last night. I read a few threads about it and followed their trouble shooting. I tested the tps by unplugging it while the car was idling to see if the idle changed. it didn't. I unplugged the air intake charge sensor while the car was at idle to see if that changed the idle speed. it didn't. I sprayed around the throttle body looking for vacuum leaks and didn't fins any. I gave up and put the car back together and it worked. the idle had returned to normal. nothing was weird. the check engine light was off. I was happy it was fixed but I really wanted to know what it was. today I started the car to pull it out of the garage and the idle shot back up immediately and wouldn't come down. the check engine light was flashing again. that in itself is odd that it flashed with the rpm instead of just staying on. so back to the drawing board on this.

 

Step 1 - what code are you getting?

 

Check engine light was flashing or on solid ?

 

check engine light was flashing. I just used a jumper to read the codes. I got a 22- tps reading low, 23- manifold temp sensor reading low, and 51 prom fault. is all of this from a prom fault? I put in an aftermarket chip about 3 months ago. its been running much better than on the stock chip until now.

 

It sounds like a bad ecm or it could be a bad prom. I would try to install your old prom and see how it runs.
erase your error codes by disconnecting the battery for 10 min or so.
the flashing engine light indicates the engine is running in limp home mode not off the prom.
you might be able to source a used ecm in the classifieds you need a service number 1228746 used in
89-92 tbi

 

I have the old prom. will put it back in tomorrow and see what what. appreciate the help guys.

 

It’s odd that the new prom would be the problem. It could be a bad connection where the prom seats in the socket.

 

I thought about it being a bad connection as well. I will verify that the chip is seated well and try again with it. besides switching the proms is there a way to verify the ecm is good?

 

You can wrap on the ecms case with a screw driver handle while the engine is running to see if it acts up.
no other test I know of to help you verify if the ecm is bad .

 

I have the computer pulled down and im ready to pull the aftermarket chip and reinstall the factory chip. will the factory chip install in the same direction as the aftermarket? both have a notch one end. I know it will install in both directions but the wrong way will fry my ecm. so which direction does the notch face? im going to pull my manual but I like checking in with you guys as well.

 

http://westersgarage.eidnet.ca/EPROM%20Procedure.pdf


this shows the direction the prom holder is inserted into the ecm. Look at the notch in the holder.

 

okay read the manual and went to install the chip. when I was removing the aftermarket chip I noticed one enc was very loose. im thinking maybe it wasn't seated. I guess its possible it vibrated out. the factory chip was in a plastic holder. the aftermarket chip didn't come in a holder nor did the instructions say to put it in one. so maybe the lack of the chip being in a holder is the culprit? I pushed the aftermarket chip back in and everything is working fine. im going to give it an hour then try again to see if its working. would be nice if this is just a case of a loose prom.

 

Pin #1 is identified by a dot, or to the left of the notch, for those that don't know.

 

took the car out for about 15 miles. it ran great with none of the issues. im hoping that the loose chip was the issue and this will stay running right. last time I unhooked the battery the computer reset and it ran correctly for about 5 miles. I feel like ive driven far enough that I would know if it was going to fail again. will find out for sure tomorrow.

 

I'm pretty confident you've found the problem.

 

Can’t believe someone sold you a prom without the holder. It really helps secure The connection.

 

I have some errands to run tomorrow. it will be plenty of miles to know for sure if ive got this thing beat. need to buy a holder for this chip.

 

Look at the junkyard for a holder 87-92 tbi trucks they are behind the glove box insert.
i have some but only have flat rate small shipping boxes so shipping would be a killer for such a small part.

 

Im far enough into driving miles now to say this has been corrected. The prom had vibrated loose on one end. I guess this is a best case. For now im going to tuck everything back under the dash. If this happens again i will need to locate a holder. Thanks to everyone who jumped in with advice to help me keep my bird flying.