I bought the A6 with a broken timing belt, took care of the valve damage and put it all together at the weekend.....

It ran lumpy at idle so I waited for a code on my OBDII software and eventually it came - P0305 (misfire on cyl 5). I switched coils, nothing. I replaced plugs, nothing. I changed over the amps on the air cleaner box, nothing. Later came a P0303 (misfire on cyl 3), so not a problem with a whole bank, must be common to both.

I did go for a drive and it ran very well for a bit then got very shaky so I took it home. I was low on coolant (not really low, just low enough for the level sensor to complain. It was shortly after the coolant alarm that the car ran worse - related???

If it is not isolated to one bank, can I rule out EGT, O2 sensors, ignition amps on air cleaner box.... unless I have a failure on both banks? The car ran very well prior to the belt breaking according to the previous owner.

What does an intake leak feel like? Especially after the turbos?

I double checked my cam timing tonight and it is perfect with the cam bar. I am fresh out of ideas, maybe next step is to use VAG-COM, but I don't have it.

Thanks for taking the time to read this and I appreciate any pointers that you may have!

 

Are you getting fuel?
I have mifire codes when the fuel pump went bad at 115k miles and nothng wrong with the ignition system.

 

I'll have to get a fuel pressure tester, but it drove very well, briefly, so I want to believe that the fuel side is OK. Worth a check though and Harbor Freight is on the way home!

I'm reading about torn throttle body boots at the moment - do my symptoms sound similar? Rough idle, jerking? The jerking is like being in a gear way too high for the road speed.

 

A vacuum leak after the turbos will become a boost leak under boost. Does the misfire go away when you get on the throttle? If not, it is not a vacuum leak. It could be a headgasket issue. Did you have the heads checked for flatness?

Bob

 

From memory, it shudders less when revved up a bit. I have the covers off right now so I can't run it to find out. I will pay very close attention to the boost piping when I reassemble this evening. My engine has very few vacuum lines because it has no SAIP or EGR and what little is there is in very good shape.

Regarding the heads, I did not have them checked for flatness because the car had not experienced any overheating problems. It did run extremely well for a few minutes, plenty of power and nice and smooth. I think if I had any serious mechanical issues it would have been running very rough from the start.

It was after a good launch that the shuddering started. I didn't rev it very high, but I would imagine the boost pressures got up there.

 

"I bought the A6 with a broken timing belt, took care of the valve damage and put it all together at the weekend"

Would you elaborate=> damages and repairs?

 

The damage was all 12 exhaust valves had bent stems and three intake valves on the 1-2-3 bank - the middle valves on each cylinder. I replaced all valves, lapped them into the seats, new valve stem seals. The guide clearance was within the spec as best as I could determine and had no visible signs of wear or damage. One lifter had a bad check valve and would not hold oil, so I replaced it. I don't have what I would consider excessive valvetrain noise - I have an Audi A4 2.8 to compare it with.

The cam location marks line up dead on with the bearing cap arrows and I counted 16 chain rollers many times. I have messed this up before and know how annoying it can be so this time I checked MANY times. I have the cam locking bar but I chose not to use the crank pin because access looked very tricky, instead I used the harmonic balancer and the reference mark. I re-checked last night and everything was perfect - bar just slid on.

Of course everything that contacts the timing belt is new, new head gaskets and bolts, etc. I took a similar approach on a Passat not so long ago and had no problems at all which is why I am a bit perplexed.