[scottro]

Car seems to have a slight misfire or studdering when accelerating with about half throttle. Under WOT, runs smooth. Throws no codes.

Just replaced the plugs, did not improve. Any suggestions?

Recently returned to stock after running Procede + Meth for awhile.

[lfelunden]

How about checking the coils? Make a compression test etc

[patrick335i]

Pull out your spark plugs, any fuel on the plugs? Also checking the coils is a smart idea.
Could be fuel injectors however it's odd you don't have any codes, probably an early warning of a bigger problem.

[sammy_0559]

time for an intake clean.

[Iceberg3232]

Originally Posted by sammy_0559

time for an intake clean.

Walnut blasting needed...

[vanondemand]

My car stuttered when one of my coil packs was broken causing the curernt to arc.

[scottro]

Thanks for the replies guys. I figured coils would be the next thing to check, but the fact that it runs fine under load is throwing me off. If a coil was bad, wouldn't it be worse under heavier loads?

Does a VANOS issue make any sense? With the Procede on and running more boost than stock, I could rather frequently trigger the VANOS solenoid code. Rebooted the car and it would come out of limp mode and run fine. I've never been able to trigger the VANOS code running stock boost, though ...

[Iceberg3232]

Originally Posted by scottro

Thanks for the replies guys. I figured coils would be the next thing to check, but the fact that it runs fine under load is throwing me off. If a coil was bad, wouldn't it be worse under heavier loads?

Does a VANOS issue make any sense? With the Procede on and running more boost than stock, I could rather frequently trigger the VANOS solenoid code. Rebooted the car and it would come out of limp mode and run fine. I've never been able to trigger the VANOS code running stock boost, though ...

I guess you ignored the two posts about having your intake valves cleaned? This explains why the car stutters under medium load also...

[scottro]

Originally Posted by Iceberg3232

I guess you ignored the two posts about having your intake valves cleaned? This explains why the car stutters under medium load also...

I haven't ignored them, but I was hoping for other suggestions that might make sense. I had the intake off ~5-7k miles ago while replacing a HPFP and inspected the valves then. Some build-up, but not too bad.

[fazman]

Maybe you should switch over to using a JB4

[Gon]

I had this on my car, could either be one of the coil packs or fuel pump. How many miles do you have?

[dicostal]

I had a bad injector and had similar symptoms, although my studdering was there all the time and very severe, but at higher RMP it got better or less noticeable. Not sure if this helps, but from the other post it sounds more like carbon build up.

[scottro]

Originally Posted by fazman

Maybe you should switch over to using a JB4

Haha! Funny thing is this happened after removing the Procede! Ran great with the Procede installed!

[scottro]

Originally Posted by mechtm

I had this on my car, could either be one of the coil packs or fuel pump. How many miles do you have?

I'm thinking coil pack or fuel pump related as well. Although I just installed the HPFP not too long ago so I hope that's not it I'm surprised that the computer isn't throwing any codes though as I thought it was pretty sensitive around these components failing. Just rolled over 55,500 miles.

[scottro]

Originally Posted by dicostal

I had a bad injector and had similar symptoms, although my studdering was there all the time and very severe, but at higher RMP it got better or less noticeable. Not sure if this helps, but from the other post it sounds more like carbon build up.

Thanks for the feedback. Yours does sound more severe, mine isn't noticeable at idle and I could even accelerate to 45mph with light throttle and not notice it. It's when I go about 40-60% throttle it will start studdering a bit (although RPM's still climb relatively effortlessly, just with the noticeable misses) and I don't see the issue at WOT.

[CHECKERED]

Coil pack would throw a code,
injector will throw a lean or rich code on that entire bank.

Without a tune there is no way to do logs lpfp or hpfp to see what it happening.
Maybe clean vanos solenoids
intake cleaning will help and eliminate that as a possible problem

[scottro]

UPDATE in case someone comes across this thread with the same symptoms:

After replacing spark plugs and bought a new coil and rotated it through all 6 cylinders, the problem was still there.

Decided to give intake cleaning a shot and went with soaking the valves in a cleaner and manually scraping off all the build up. It still has a stutter at idle which the car has had since day 1 that I've had it (others report intake valve cleaning smooths out the idle, doesn't seem to be the case for me), however my misfires and hesitation to accelerate in the 2-4k RPM range under medium throttle appear to be gone!

What a pain in the ass this was! If I had to do it again I think I'd invest in the walnut blasting approach.

Thanks everyone for the suggestions.

[marcvtec]

Try resetting the adaptions and go wot a few times
Check the battery, different fuel station etc.
Stock clutch, flywheel ?

[scottro]

Originally Posted by marcvtec

Try resetting the adaptions and go wot a few times
Check the battery, different fuel station etc.
Stock clutch, flywheel ?

I no longer have a procede installed.. are there other adaptations to be reset?

Yes, stock clutch/flywheel.

[Jeff@TopGearSolutions]

Originally Posted by scottro

UPDATE in case someone comes across this thread with the same symptoms:

After replacing spark plugs and bought a new coil and rotated it through all 6 cylinders, the problem was still there.

Decided to give intake cleaning a shot and went with soaking the valves in a cleaner and manually scraping off all the build up. It still has a stutter at idle which the car has had since day 1 that I've had it (others report intake valve cleaning smooths out the idle, doesn't seem to be the case for me), however my misfires and hesitation to accelerate in the 2-4k RPM range under medium throttle appear to be gone!

What a pain in the ass this was! If I had to do it again I think I'd invest in the walnut blasting approach.

Thanks everyone for the suggestions.

So at 55,000 miles you basically needed an intake valve cleaning to avoid misfires.

This should help others that have yet to get an intake valve cleaning. I usually recommend them at 35,000 as there is substantial build up by then.

Although I can see why one would wait for a problem before getting it done too.

[scottro]

Originally Posted by Jeff@TopGearSolutions

So at 55,000 miles you basically needed an intake valve cleaning to avoid misfires.

This should help others that have yet to get an intake valve cleaning. I usually recommend them at 35,000 as there is substantial build up by then.

Although I can see why one would wait for a problem before getting it done too.

Yup.

And for anyone looking to do this themselves, I found an o-ring pick to be the most useful for cleaning off the build up not only on the valve stem but getting behind it and near the bottom of the valves. Something like this:

http://www.gearwrench.com/auto-speci...tml?feedback=1

Very time consuming process. I felt like I was a dentist for a day cleaning plaque off my car's teeth.

Also, a radiator hose removal tool like this: http://www.handsontools.com/OTC-4521...l_p_48972.html was helpful to remove that damn connector holder that is attached to the bottom of the intake manifold. It allowed me to get behind it and pry up so I could slide it off. You may have to modify it a bit, as the one I have was basically a phillips screw driver with the tip ground off and to a point, and then bent similar to the angle in that picture. Not sure if that one linked will work exactly out of box for you or not.

[marcvtec]

Originally Posted by scottro

I no longer have a procede installed.. are there other adaptations to be reset?

Yes, stock clutch/flywheel.

Yes the ecu stores it all, I would reset them since now you took the tune out and the car needs to adapt to stock parameters