View Full Version : slight engine miss

05-21-10, 10:14 AM
96 sts. 120k miles. just won't idle right. runs ok but i get a slight stumble at times. owned for 10 yrs so its my project car now. only driven 10k miles in the last 3 yrs. did headgaskets 3 yrs ago. new intake gaskets. changed intake plenum cuz i overtightened old intake and cracked it. new delco plugs. plug wires are 5 yrs old. new regulator. engine starts but idles funky for 30sec. does not use any coolant. never checked heads for flatness or cracks. pretty sure i got timing right. i assume cam followers are ok. when i turn on a/c the motor really starts to stumble. very erratic idle. turn off a/c and it really runs better. any ideas? i think putting the engine under load with the a/c points to an ignition issue. but the stumble might be a vacuum leak somewhere? pcv stuff all looks good. i tried a different(used) ignition control module and coil assy. no difference.

05-25-10, 10:19 PM
Do you have any service engine light on? My sisters 96 seville sts was doing something simialar, it turned out to be the egr valve was sticking open or something like that. I replaced the mass air flow sensor and a bunch of other things before i found out what it was.. It was not triggering the check engine light so it was difficult to pin point the problem.. Also try cleaning your throttle plates with carb cleaner and a tooth brush..

05-28-10, 04:35 PM
i have gotten several egr codes, p1406 but it usually will idle poorly as well. than it will clear itself. i can usually make the egr code set if i punch the motor while cold and stop fast. usually will set code in a block or 2 of driving. does not seem to occur if i drive hard when warm. sure points to a sticky egr valve.

05-28-10, 04:52 PM
That's where I'd start.

05-29-10, 10:33 PM
cleaned throttle plate. took off egr and cleaned pintle. sooty of course. easy job. car seems to run a bit smoother. still not sure i want to spend 130 for egr. car seemed to start better when hot. perhaps cleaning throttle bore makes a slight difference. have taken off IAC before. would be nice to change maf, map, iac, egr to see if it helps any.

06-04-10, 06:56 PM
disconnected battery for 1 hr today. started car and it is purring. moved it in/out of garage and did not drive on road but it is super smooth idle. only temporary i am sure.

06-07-10, 10:34 AM
drove about 100 miles this weekend. idle is ok but still not perfect. if i am driving at about 20 mph and give it 3/4 gas, the engine will stutter. it never used to do that. always had fairly smooth acceleration. i have been getting code P0140 and P0141 occasionally but i just started getting P1339. o2 sensor crosstalk count is funky? i clear codes and they may/maynot come back right away.