Northstar Engines and System Technical Discussion Discussion, 96 STS High Idle After Highway Run in Cadillac Engine Technical Discussion; Our 96 STS runs normally around town but after 1/2 hr highway idles at 1200 to 1500. Seems like it ...
Our 96 STS runs normally around town but after 1/2 hr highway idles at 1200 to 1500. Seems like it will come down after shutting off and starting again. Is the computer confused? Not sure at all what is wrong.
Replaced the plugs 6 months ago due to misfire, helped but not completely. Seems the mileage dropped before I changed the plugs. Used to get 20+ average, now getting 17. Driving it hard with WOT will bring on Service Engine light which then goes out after some normal driving. There were a few codes one being misfire. Car has 150K miles and does not overheat.
Pulled the codes:
PC0139-HISTORY P0139 - Heated Oxygen Sensor (HO2S) Slow Response Bank 1 Sensor 2
PC1406-HISTORY P1406 - EGR Valve Pintle Position Circuit
IR1771-HISTORY Could not find specific code Integrated Radio????
On clearning codes it will go for 2 or 3 days without new codes, then the service
engine light comes on, with new codes. Then days later it often goes off again.
I believe that the electrical system is flaky, but am certainly open to suggestions.
Some time after I changed the plugs I put Techron in it and about an hour later
the service engine light came on. After the next fill up it went off.