RS2 hesitating at light load

[RS2 driver]

My RS2 (ADU) in standard trim has got a slight hesitation only at light/medium load, i.e. easy at 2500-3500 rpm in 3rd gear.

It is most significant when engine is cold, but is also present when engine is at normal operating temperature approx. 90 deg C, although not as distinct.
At WOT no hesitation can be felt and a dyn-test last year showed engine capable of meeting the stated power of 315 HP and 400 Nm. The spark plugs were recently changed to NGK BKR-7EIX from the original Bosch F5DPOR ones. To eliminate the spark plugs as source of this problem the old Bosch plugs was installed again, but problem persists.

Any suggestions are welcome.......

[ruby-s2]

I had a similar problem with mine last year and it was a coil failing, i replaced all 5 and that cured mine.

[UrS4boy]

Any suggestions are welcome.......

Try some of the tests in this missing and hesitation diagnostic, including coil testing and POS testing:

http://forums.quattroworld.com/s4s6/msgs/22611.phtml

[newsh]

I had a similar problem on my coupe, only missed at very light load between 2500 and 3000 rpm, would sometimes stumble coming back on the throttle from coast. It was a small boost leak in the ISV pipework, the split in the elbow pipe was under the jubillee clip and was very difficult to find even with a full boost leak pressure test.

[Ross]

Could be coil packs but I'd expect them to really show when it's on boost. Do you have history of when they were changed?

It may be worth pulling codes if you can, but check over the hoses - I'd second that a small leak sucking in air could upset it a bit. Does it look like the boost and vac hoses are original? I'd guess they probably are if its never been remapped.

[veneto rs2]

I had a similar problem on my coupe, only missed at very light load between 2500 and 3000 rpm, would sometimes stumble coming back on the throttle from coast. It was a small boost leak in the ISV pipework, the split in the elbow pipe was under the jubillee clip and was very difficult to find even with a full boost leak pressure test.

Same to me the same elbow (NLA from Audi) same problem.

Like Ross I would expect if it's a coil related problem to show up also on boost.

Stefano

[RS2 driver]

Thanks for input

Dave I have already been looking at the link you refer to and will try to make a test of ignition system.

However not sure if its ignition related when the hesitation is ONLY noticeable at light load, and not if car is pulled trough the gears at WOT. Have also checked fault codes but found none.

I have been wondering if the ISV could cause this problem and will definitely check out the pipework for any boost leaks. Also wondering if it can be MAF related.
I guess most of the vac and boost hoses are original, might be a challenge if they are NLA from Audi.

Car is presently garaged for winter time but always nice to be prepared for starting up again......

[RS2 driver]

Today I just made a quick boost leak test, by simply put a bung at the MAF-turbo hose.

When pressure is applied air is coming out of oil filling in topcover. Is that normal?

Tomorrow I will try to plug the crank case breading hose and test again.

[RS2 driver]

Have now done a further boost leak test, by plugging the PCV system and applying 1 bar pressure to remaining system. A small leak at the non return valve was rectified and pressure drop from 1 bar to zero is around 15 sec., should that be considered OK?

Suspect the PCV valve to be defective and will be changed.

Very minor leak could also be seen at a couple of the injectors, renewing seals and test of injectors will be considered a job for the long dark nights….

Also when applying pressure a bubbling sound can be heard from the crankcase sump, suppose air is escaping trough oil lines from turbo charger, is that sounding reasonable and should it be of any concern?