Hi all,

I'm trying to diagnose my car occasionally stalling. It's a 2009 R56S auto, with 86K kms (53K miles). Car has never been tracked, has been tuned with an Alta AccessPort for most of its life. Recently, it's been occasionally stalling when in 'D' and stopping on red lights/stop signs. Restarting the car works fine and it runs fine for a while. I've not been driving it a lot in the last few months at all, so I can't say with which frequency it happens, but let's say if driven 2-3 hours per day on average, then it'll maybe stall once a day.

I admit to not having diligently verified oil every day, but oil's been changed roughly every 10-11K (7-10K miles). Most recently a few weeks ago. This has not addressed stalling. There's a 'superknock' code logged in the DME that's been persistently sitting there for at least a year; dealer ignored it in the past, and now warranty is out.

No other major engine-related maintenance has been done (belts, spark plugs, coils, etc).

What should I consider doing next? Should I replace spark plugs and/or coils, or is this randomly throwing money at an unknown problem? Should I scan/diagnose more? I have both a Bavtech and an INPA cable, so I can scan anything needed.

 

Bumping the thread. Ordered new spark plugs but still wondering if I should do coils or not and what else to consider.

 

Try replacing the coil packs as well. Have you also had your valves checked for Coking. You could be suffering from coked up valves and it could cause it to idle rough and/or stall

 

Thanks. I've not ordered coil packs yet; should I replace both at the same time, or start with spark plugs in case that addresses it? (or do coil packs have to get replaced around this mileage anyway? Don't want to unnecessarily blow away $250 or whatever they cost...)

How do I check coking on valves? Does the head have to come apart for this, or will the spark plugs tell a story?

 

First check your spark plugs since that is the easiest and cheapest repair if it is needed at all, a fouled plug can cause all sorts of problems especially if you have carbon buildup on the intake valves. The head doesn't need to be removed for the intake valve check and or cleaning, the plastic intake manifold needs to be removed which isn't that hard. After you get the intake manifold off find a strong flashlight and then you can see your valves. I like flashlights that allow you to focus the beam of light because you're going to need a narrow beam to be able to see down those long small diameter intake runners. Have you tried removing the tune to see if your problem persist?

 

Haven't tried removing the tune yet as I was preserving the fault codes. The car ran fine for a number of years, so it wouldn't have been the tune ... at least not originally. I suppose if there's some carbon buildup, then the tune could be making things worse.

I guess I will first switch the spark plugs and check the valves; then remove the tune, one step at a time. If that doesn't help, then coil packs ... and then bang my head on the wall for lack of any other ideas

 

Just a hypothesis, the tune could have brought this on and is just now starting to show. Maybe even more carbon build-up than (usual) normal.