1999 Pontiac Bonneville Runs rough only for a few seconds w

PANCORDION

MEMBER
1999 PONTIAC BONNEVILLE
6 CYL
2WD
AUTOMATIC
147,600 MILES

Engine runs rough for only a five or so seconds when first started for the day. Then, engine light came on immediately. It runds smooth after being started the rest of the day and smooth on restarts. Then, after 3-4 days the engine light went out. On subsequent days it started up smoothly. Then, after about 10 days, the same thing happened, started up rough for a few seconds, then engine light came on. Ran smooth when driving and when restarting the same day. After 3-4 days, the engine light went out again and the car started each day smoothly. Then, yesterday, same thing all over again. Started up a little rough in the morning and the engine light came on. Then runs smoothly the rest of the day, including restarts on the same day. I suspect the engine light will go out again in about three or four days and it will be smooth starting for 10 days or so. This keeps repeating itself. What could it be? Could it be an oxygen sensor? The car was totally serviced in April, six months ago. Only put 2000 miles on it since. The service included new plugs, new spark plug wires, new fuel filter, state inspection, etc. It's been a great car this 1999 Pontiac Bonneville, 6 cylinder.

5 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Have the computer scanned for code/s-you have a problem within the engine management system that caused the CEL to turn on-This is your starting point of diagnosis, finding out what's going on.

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Wednesday, November 3rd, 2010 AT 7:24 PM

PANCORDION

MEMBER
3 POSTS

I already knew it needed to be scanned for codes. By the way, the engine light went off this evening, only one day after coming on. No performance problems with the car, good gas mileage, no hesitation, plenty of V-6 power.

To be redundant, this started about three weeks ago. Start car in morning, runs rough for five or so seconds, engine light comes on, then runs smooth the rest of the day, including restarts on the same day. In a day or so the engine light goes off, car continues to run smooth. 10 days from now, start up in the morning, runs rough for 5 seconds, engine light comes on. Runs smooth after that all day. Then, a day or so later engine light goes off and car continues to run smoothly even on the first startup the next day. Keeps repeating this every 10 days or so.

What are the probable codes and define each. Computer scanning costs some bucks, it's not cheap. Thanks.

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Wednesday, November 3rd, 2010 AT 10:15 PM

RASMATAZ

MECHANIC
75,992 POSTS

Go to Autozone or Advance auto they'll do it for free -BTW I know its not cheap and its not cheap to have one too! In today's technology the automotive technician is useless w/o it-Everything is money now a days and it talks for you-same goes to me its costing me money helping people in need here.

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Thursday, November 4th, 2010 AT 3:34 AM

PANCORDION

MEMBER
3 POSTS

Read my previous messages for familiarization again.

Went to Advance Auto. Free computer diagnotic done. Read: "Number 6 Cylinder misfire"

Not having any performance problems, good gas, smooth driving, etc. Again, engine light came on Saturday after car first started up and ran rough only for about five second, then smooth. Light stayed on until this morning, Monday, started up, ran a little rough for five seconds then smooth and light went out.

Agaiin, back in April had new plugs, new plug wires put on and new fuel filter. Less than 3000 miles put on the car since late April.

What are the optional probables for #6 cylinder misfiring and the estimated cost of each? Thanks.

Tom

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Monday, November 8th, 2010 AT 2:31 PM

RASMATAZ