1991 Idle/Over Drive Problems

I have a 91 PA with 130,000 miles on it. A week ago I put Sea Foam in the gas tank. Now I'm having strange things happening with the idle and over drive. I don't know if the Sea Foam caused this or if it's just coincidence.

I drive through several stoplights to and from work at freeway speeds of 70 mph and town speeds at 30 mph. The idle will go from normal at one light to high at another light to low at yet another light. When it is high the car will do 40 with no gas. I have to put it in neutral at a stoplight because I'm afraid the brakes won't hold it back.

The over drive is also acting up. Sometimes it will not shift into over drive. The other day I had the cruise on at 70 mph and all of a sudden the cruise disengaged and the car came out of overdrive.

Any ideas on the cause of these problems? Are they related? Can someone give me a step by step guide to diagnose?

Thanks.

Click Here (http://www.automotiveforums.com/vbulletin/showthread.php?t=679458) to get started and let us know what you find.

I'm still confused on why I can't get the diagnostic mode to work. Where is the check engine or service engine light on the 91 Park Avenue? Is it on the dash near the speedometer and tachometer? Or is it on the little area above the dash?

The reason I ask is I don't remember seeing any engine light come on when I start the car. I did have the car serviced last fall because my headlights stopped working. The pinpointed it to a bad lighting control module and instead of replacing it, I just had them jumper it so the lights would work. Could this be why the check engine light doesn't work? I do still have the red indicator lights on the dash.

I've seen posts in which people mentioned taking the car into an auto parts store and getting the codes checked. Will most stores do this for free? Do they have the scanners for a 91 Park Avenue?

Thanks.

BTW, where are the other posts to this thread? Both myself and HotZ28 posted replies over the weekend. Now they are missing.

Click Here (http://www.automotiveforums.com/vbulletin/showthread.php?p=5773512) for info on the missing post. I lost about 10-15 post, they just vansihed! :screwy: Part of the database is still inactive, so AF is now “physically challenged” and rambling along with the aid of a crutch. Hopefully things will be back to normal soon! EDIT: Looks like everything is now working! :grinyes: EDIT: 7/18/08 ** Well, I spoke too soon! We now have missing post & error messages again. :confused:

None of the parts stores I know, have an OBD1 scanner. :grinno: Unless you know someone who still has one, you are stuck with the terminal A&B jump. Of course, if your light does not work, you are just stuck! The CEL is located in the little area above the dash. Without seeing what they did to bypass the LCM, there is no way to offer advice on this. :shakehead

So now I'm sidetracked and looking for an electrical problem. I'm trying to find where the CEL is in the circuit. I've looked at the wiring diagrams in both Haynes & Chilton. I've also looked at the wiring diagrams on AutoZone. Neither one seems to look like my car wiring and neither one shows the CEL or the light control module.

Do you by chance have a GM wiring diagram for my 91 PA. My engine code is L. If not, can you help me find the wiring to the warning lights above the dash? Is there a fuse or relay for the warning lights?

How does the lighting control module work? Doesn't it just control the headlights? It doesn't control the warning lights does it?

Again, thanks for you help.

I believe the SES light will be in the area on top of the dash... This light should come on when you start the car..

Everything you have described leads me to believe that you have a Bad TPS...

But be sure thats the issues before replacing it...

That's exactly what I'm trying to do, but in scanning for diagnostic codes I found out my SES light doesn't work. Therefore I don't get any diagnostic information. In fact, none of the lights in the area on top of the dash work. So now I've gone from checking the TPS to finding out why none of the instrument cluster lights work.

I went to the library today and looked through a Mitchell manual. It puts the Chilton's and Haynes books to shame. I copied a bunch of the wiring diagrams for my PA and now I have a place to start looking. It also has a procedure on checking the status of the SES light and what to do if it doesn't come on. It has basically led me to the ECM/PCM to check and see if it is closing the switch to energize the SES.

How easy is it to get at and remove the ECM/PCM? Is it more than a six-pack job?

Thanks.