View Full Version : random miss at idle

03-14-08, 09:39 PM
96 STS. 110k miles. i did the headgaskets last fall. stored over winter. am driving now. 500 miles total. car starts fine but has a random miss at idle. seems to accelerate fine and cruise down the road fine. seems to have good power. i have no codes. new wires and plugs last fall. i can feel the miss at a stoplight but if i put it in neutral, it feels ok. i used ac delco single platinum tip plugs. would the 41-950? plugs make any difference? of course the motor was totally apart so every connector and hose was unplugged. lots of opportunities to get something hooked up wrong. i did not put on a new intake manifold gasket. old one looked ok.

03-14-08, 10:07 PM
Hard shot to call unless you get a code to set. I'd start by going through the old tried-and-true troubleshooting: plug wires, plug boots (moisture), plug gaps, intake bolt torque, air leaks, injectors. Heck, run a 20 oz. jug of TECHRON through it. It won't hurt a thing and may help. I really doubt that a change to 41-950's would be the answer, other than plug longevity (75,000 vs. 100,000.....!) Yes, go back through the connectors, particularly the ignition signal and PCM (ECM ?) multi-pin units. Idle air valve/motor and TB clean ??

03-14-08, 10:55 PM
I had the same poroblem ........I would say exactly, on my 1995 STS, intermitant miss at idle, other wise the car ran great. I had the 100,000 mile tune up performed (car only had 70,000 on it but was 12 years old), but that didn't cure it. I took it back to the dealer, where the service rep said it might be the head gasket ((told me if it were I would have to buy a new engine, as dealer would repair it! (Prompted my first visit to this forum.)) the dealer tested it and found nothing wrong. However, the miss continued at idle for another few months .......and then half the engine cut out! One of the coils had completely died. Replaced both the coils, and quess what ...... no miss at idle! Don't know if a faulty coil is the cause of the miss at idle in your car, but it apparently was in mine!

03-15-08, 06:29 PM
i pulled the motor out the top so i did not unplug the ecm per se. i did unplug the connectors on the coil pack though. i have been chasing a miss for 3-4 yrs and put on 2 sets of ac delco wires and 3-4 sets of different plugs and the miss seemed to go away and come back. i really think the coil connectors were to blame. i used contact cleaner and it seemed to fix the problem. maybe since they were unplugged for several months i had some corrosion issues.

03-16-08, 08:59 PM
I have the same problem with my 95 STS, Replaced plugs, wires, coils, FPR, cleaned tb I still have a miss at idle. I was told it could be an injector leaking. how can i check the values of the injectors? Any help would be great!!! My car has been running like this since a little after i bought it, I just want it to run like a Cadillac again.

03-17-08, 06:05 PM
Best thing for injectors is to take them all to a re-builder and they will flow test all 8 and you will see which ones need to be cleaned or replaced.