Intermitant missfire and idle while in gear(auto)
Intermitant missfire and idle while in gear(auto) Hey guys, need a little direction here...
Just picked up a 99 T/A with A4 tranny. Car has 170,000mi on it and is very clean and looks to have been well cared for. The car runs great w/o any perceptable missing while driving. Idling good in neutral with a very occassional miss but nothing much. When i put it in gear idle drops to 400-500rpm and has an intermitant miss. Feels/sounds like a dead miss but its not consistant at all. Does it every few seconds, but its not regular at all. The previous owner told me he just replaced the plugs and it did'nt help. I just swapped out the AC Delco plug wire for a set of MSD's and this did not help either. If i bring the idle up using the throttle while its in gear it does not miss as much. The way it misses makes me think its an ignition problem. Def not the wires. Not 100% on the plugs but they did look like they had recently been changed when i swapped out the wires. Guess it could be a coil. There is no check engine light or anything.
Anyone have something simmilar? Thoughts?
Thanks,
-Mark
Just picked up a 99 T/A with A4 tranny. Car has 170,000mi on it and is very clean and looks to have been well cared for. The car runs great w/o any perceptable missing while driving. Idling good in neutral with a very occassional miss but nothing much. When i put it in gear idle drops to 400-500rpm and has an intermitant miss. Feels/sounds like a dead miss but its not consistant at all. Does it every few seconds, but its not regular at all. The previous owner told me he just replaced the plugs and it did'nt help. I just swapped out the AC Delco plug wire for a set of MSD's and this did not help either. If i bring the idle up using the throttle while its in gear it does not miss as much. The way it misses makes me think its an ignition problem. Def not the wires. Not 100% on the plugs but they did look like they had recently been changed when i swapped out the wires. Guess it could be a coil. There is no check engine light or anything.
Anyone have something simmilar? Thoughts?
Thanks,
-Mark
Last edited by Birdoprey; Mar 19, 2013 at 10:58 PM.
TECH Fanatic
Joined: Jul 2011
Posts: 1,074
Likes: 2
I would check the plugs again, time and time again I see people over tightening the plugs and cracking them only to cause a intermittent misfire. Also I had a set of brand new plugs in my dd for about 300 miles and then it started to misfire. I tested the coils, ICM, wires, with no problems found. I replaced the plugs and the misfire went away. The plugs were not over tightened they just went bad for some reason. Couldn't tell you why but never over look the plugs.
Is the car completely stock? It may not be so much a missfire as just too low of an idle rpm (while in gear) for it to run smooth. I'm not sure how you adjust that with an LS1 besides in the tune....or if something is wrong that is causing it to be too low. On LT1 throttle bodies there is a throttle stop screw that can be adjusted slightly.
Could there be a problem with your IAC?
Could there be a problem with your IAC?
I would check the plugs again, time and time again I see people over tightening the plugs and cracking them only to cause a intermittent misfire. Also I had a set of brand new plugs in my dd for about 300 miles and then it started to misfire. I tested the coils, ICM, wires, with no problems found. I replaced the plugs and the misfire went away. The plugs were not over tightened they just went bad for some reason. Couldn't tell you why but never over look the plugs.
Thanks for the info!
Is the car completely stock? It may not be so much a missfire as just too low of an idle rpm (while in gear) for it to run smooth. I'm not sure how you adjust that with an LS1 besides in the tune....or if something is wrong that is causing it to be too low. On LT1 throttle bodies there is a throttle stop screw that can be adjusted slightly.
Could there be a problem with your IAC?
Could there be a problem with your IAC?
That was a thought for me as well. Took a looksee at the TB the other day and it has some build up. Gonna clean that out and see if that helps any. not sure if the idle can be adjusted w/o a tune. Will have to check into that.
Thanks for the suggestion!
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Verdad Gallardo Hope you get it worked out soon.
I forgot to ask: Is the idle always at 4-500 rpm when in gear, or is that just what it drops to when it starts cutting up? If it's always that low then what I said above applies more.
I had thought about a vac leak too, but forgot to type that part. They usually give you a higher idle, but not always. While you are cleaning the TB, you might want to clean the MAF too.
I forgot to ask: Is the idle always at 4-500 rpm when in gear, or is that just what it drops to when it starts cutting up? If it's always that low then what I said above applies more.
I had thought about a vac leak too, but forgot to type that part. They usually give you a higher idle, but not always. While you are cleaning the TB, you might want to clean the MAF too.
Hope you get it worked out soon.
I forgot to ask: Is the idle always at 4-500 rpm when in gear, or is that just what it drops to when it starts cutting up? If it's always that low then what I said above applies more.
I had thought about a vac leak too, but forgot to type that part. They usually give you a higher idle, but not always. While you are cleaning the TB, you might want to clean the MAF too.
I forgot to ask: Is the idle always at 4-500 rpm when in gear, or is that just what it drops to when it starts cutting up? If it's always that low then what I said above applies more.
I had thought about a vac leak too, but forgot to type that part. They usually give you a higher idle, but not always. While you are cleaning the TB, you might want to clean the MAF too.
It sits above 500rpm when not in gear. can't remember exactally where though. It drops a bit when put into gear and thats when the miss starts. I've not had time to mess with it. I'll look into it more this weekend if i get the chance. I'll post up what i find.
Thanks again,
-Mark
Teching In
Joined: May 2011
Posts: 2
Likes: 0
I have the exact same issue... normal idle is ab 850 rpms but when in drive (rarly) the idle will drop to 450 500rpms and thats when it starts to miss.... i just replaced my Opti 2weeks ago cuz it died... just changed the wires yesturday... spark plugs are good i pulled a few out and they look fine... i havent had a chance to scan it but im thinkin its an o2 sensor or EGR lemme no what you find and ill let you know if i figure it out soon
