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Old 17-05-2010, 01:30 AM   #1
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Lumpy idle - possible reasons?

My GTT used to idle like a dream, a solid unbroken purr that settled down to about 680-750 once the block warmed up. After a track day last year, it got a bit lumpy, sounding like it misfires about once every second or two. You can feel it through the seats and wheel quite clearly. At first it wasn't so frequent, but I think the misfires might be getting more frequent. Open the throttle a bit and it runs perfectly, but let it fall back to idle, and it stutters a bit. Any ideas what normally causes this?
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Old 17-05-2010, 03:36 PM   #2
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Boost leak, broken manifold studs, spark plugs, coilpacks.

Check all them
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Old 17-05-2010, 03:48 PM   #3
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I vote spark plugs!
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Old 17-05-2010, 04:15 PM   #4
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okay do all the usual checks the guys there have mentioned.

here's one you might not have thought of tho - when Ian removed top half of my plenum we were quite surprised to see that upon removing the outer bolts the middle ones (the bitch ones underneath) were actually quite loose creating a rocking effect on the plenum. this had warped the gasket between the two halfs and also created a serious leak. As a result misfires/missing on idle and very rough running overall along with a noticeable hiss/leak from the plenum.

just something to think about mate
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Old 18-05-2010, 03:09 AM   #5
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my R33 GTR was doing the exact same thing, it was a leak in the plenum or inlet manifold gasket...spray some carb spray all around the plenum gasket area and see if the engine speeds up...
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Old 18-05-2010, 04:08 PM   #6
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my R33 GTR was doing the exact same thing, it was a leak in the plenum or inlet manifold gasket...spray some carb spray all around the plenum gasket area and see if the engine speeds up...
GTST/GTT's are less prone to that but good point.
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Old 18-05-2010, 11:01 PM   #7
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Thanks for all the suggestions - I will have a good look and see what I can see. In fact, although I've owned the car since last July, the parking I used to have was mechanical - you park in a garage and then when the doors shut, a giant machine whisks the car off into the bowels of the building somewhere. Because of this and the law that it's illegal to idle on the street in Tokyo, I've never even really looked in the bay when the motor's running. I'm going down to Southampton on Friday to pick my car up off the dock (after 2.5 lonely, lonely months) so I'm really looking forward to getting my hands dirty and learning something about my car. So thanks for the initial pointers guys!
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Old 19-05-2010, 11:55 PM   #8
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Lumpy, idle, sounds like my wife.
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Old 20-05-2010, 08:48 AM   #9
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Lumpy, idle, sounds like my wife.
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