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highwaywarrior
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Name : daryl
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PostSubject: missing at idle   Tue Dec 24, 2013 11:36 am

Noticed a couple of days ago that my buick has developed a miss at idle both in park and drive. Plugs and wires are about 5 months old. I havent changed the coil packs yet. Theres no check engine light. It doesnt hesitate under any throttle position. Do you think its my coils? IAC etc.
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LARRY70GS
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PostSubject: Re: missing at idle   Tue Dec 24, 2013 1:01 pm

If it was a persistent miss, you would get a CEL. It would also tell you which cylinder was missing. If you scan the engine, you can look at the misfire history for all 6 cylinders. The PCM keeps track of the misfires with an actual counter. Each coil fires 2 cylinders pairs. Those pairs are called companion cylinders. On our engines, they are 1-4, 2-5, and 3-6. If the misfire history reveals misfires on a pair of companion cylinders, I'd suspect that particular coil, but not otherwise. Do some diagnostic testing before you replace parts unnecessarily. Just my .02

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98 Riviera SC3800  All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU
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deekster_caddy
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PostSubject: Re: missing at idle   Tue Dec 24, 2013 1:05 pm

That sounds more like dirty fuel injectors to me. I was amazed at the difference in idle quality after I had mine bench cleaned. It would miss and sometimes 'spit' a little bit. Like there was raw gas dripping into a cylinder that wouldn't fire right, and sometimes it would pop in the exhaust pipe. After clean injectors - smooth as silk.

Try disconnecting one injector at a time and see if one of them makes the idle smooth out.
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highwaywarrior
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PostSubject: Re: missing at idle   Tue Dec 24, 2013 1:09 pm

Yup no check engine light. Its definitely an erratic idle. WOuld a vacuum leay2k cause this? If so, what would i use to detect it. Cleaningthe injectors is a good idea
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highwaywarrior
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PostSubject: Re: missing at idle   Tue Dec 24, 2013 1:20 pm

And yes the tach needle does go up and down, id say no more than two tick marks. Whats the worst that can happen?
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LARRY70GS
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PostSubject: Re: missing at idle   Tue Dec 24, 2013 1:39 pm

Just put a vacuum gauge on it. I have a vacuum/boost gauge on mine. It pulls a steady 20" of vacuum at idle, in Park, fully warmed up. Anything less than that, you have a vacuum leak.

_________________
98 Riviera SC3800  All stock except gutted air box.
1970 Buick GS455 Stage1, TSP built 470BBB, 602HP/589TQ
Best MPH, 116.06 MPH, Best ET, 11.54
https://www.youtube.com/watch?v=UHCda-t_Jls
https://www.youtube.com/watch?v=sfT2tEO4XcU
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highwaywarrior
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Name : daryl
Age : 34
Location : chesapeake va
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Post Count : 403
Merit : 2

PostSubject: Re: missing at idle   Tue Dec 24, 2013 3:04 pm

Wait a minute. My aeroforce gauge reads boost. But at idle i think it reads vacuum in the negative. Itll will jump from -19 to -17.9
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