QuestionI also have had this problem of High Idle in drive when the car is moving. Once the vehicle realizes it has stopped moving the idle kicks down. I have been to the dealer 3 times for this and they try to reprogram the ECM with no change in drivablity
AnswerHi John,
If you have been to the Caddy dealer and 3 times isn't the charm then all the oldtimers must have moved on. It is a rather involved procedure to get all the adjustments done correctly and because of the age of your car the throttlebody shaft bushings could be egged out causing a vacuum leak and a higher idle.
Here is the procedure that I have used and if you want to go back and have the tech follow along, hopefully he will be able to get a normal idle.
1) Open the throttle plates and clean any carbon from the bore and plates with carb spray or throttlebody cleaner and a toothbrush.
2) Warm the engine up until the thermostat opens, jumper A to B on the ALDL connector and adjust base timing to 10 degrees BTDC. Remove the jumper.
3) Hook up a tach and start the engine. Jumper the alternator ground lead to disable it. Charge light will turn on. Enter diagnostics and retract the ISC motor so the throttle lever is on the stop screw and unplug the isc wire connector. The engine might quit when the ISC is retracted. Turn the idle screw in a turn and restart the engine. Adjust to 525rpm and .50V TPS...I know the bulletin says .55V at a different RPM but this way works better. If the screw is backed off and the idle won't come down or the throttle plates are sticking in their bores then the throttle shaft bushings might be leaking vacuum and a different throttlebody will be needed or drilling and installing bushings could be done.
4) Turn the engine off with the key on, plug the ISC connector back together and extend the ISC to the max. and adjust the the ISC bolt to 1.17V TPS, then back the ISC to aprox .55V and turn the key off.
5) Wait 2 minuets and after reconnecting everything start up the engine and check the idle. If still higher than normal try the idle relearn again after disconnecting the battery and that should take care of it.
There is a special wire harness that plugs into a DVOM and into the TPS that was dealer equipment that makes it easy to see what the TPS is doing. Otherwise backprobe the TPS signal wire so you don't have to go inside to see the reading.
Hopefully that will do the trick. Bill
