Cadillac Repair: Idle Speed Control prob w/ 1989 Cadillac, negative battery cable, cadillac deville

Question
Hi Bill,
  
  My problem is that the computer code for my 1989 Cadillac DeVille for a faulty idle speed control popped up, so I installed a new one, but the car still stalls after I start it, whether the engine is hot or cold.  
  I would like to find out why you think it doesn't work.  I am a very experienced mechanic, but I need your help with this problem.
  I would like to know if you can direct me to the exact problem and possibly email me a diagnostic illustration of the problem area.

Thank you.

Sincerely,

Michael


Answer
Hi Michael,

       This site doesn't allow sending copywrited material out so you will need to crack open the manual to get that info.

       Just because a P030 pops up doesn't mean that the ISC motor is bad...it could just be out of adjustment. However if you output cycle the ISC motor through the climate control or maybe your scan tool can do it and it is noisy that would be enough to condem the ISC because it will set that code for cluggish operation.

       Cadillac is very critical of the adjustments and they need to be followed closely because you could have a low idle or possibly a 30mph idle. Start with these adjustments first i.e. timing, min air, tps and then max isc extension. Then verify that the fuel pressure is correct. I will also assume that the tune-up stuff  is ok i.e. cap, rotor, plugs and wires not causing a rough idle. Where the negative battery cable attaches could wind up being your problem. If it is still attached to the motor mount then unbolt it and clean both sides of the terminal with a sanding disc. If it is mounted on the starter "L" bracket remove it also and clean it. Then clean the block around the bolt hole and both sides of the starter bracket to bare metal. It goes engine, cable, bracket and then bolt. If you do a voltage drop to ground with alot of loads on you might see a very high number maybe even approaching 1V. Cadillac had problems with grounds that they published a bulletin explaining the procedure to use and stalling or rough running was a symptom of the poor ground.

      Try those suggestions and hopefully your problem will be fixed. Bill