2007 A6 Avant 3.2 cold start shudder/misfire still happening after carbon cleaning

[techy101]

I've got a 2007 Avant 3.2L with 190,000 miles that recently started acting up. I've been having issues with shuddering and misfiring at cold start as well as significant power loss over 4k RPM. I had done a preventative carbon cleaning back at 110,000 miles as well as spark plugs and had the injectors cleaned. Given what I've read the behavior I've seen recently points back to carbon build up.

So this past weekend I dove in and cleaned the crap out of my valves and lower intake (is this the correct name, or is it called the intake runner?). The intake manifold and throttle body looked quite good so I didn't do anything with them.

I got everything back together and there has been a noticeable power increase, especially on the top end. The car doesn't shake anymore at cold start idle, but for the first minute or two it's running if I touch the gas and get it up to ~2k RPM it will shudder and misfire a few times before calming down and running properly.

What else could be causing this problem? While the valves got scratches in them from the removal I was very careful not to do anything to the seat. (Again, is this the correct term for where the valve seals against the head?)

EDIT: I also changed spark plugs at the same time, but did not pull the injectors again as the last time they turned out to not really need cleaning. I only got a 2-5% flow improvement.

Any help would be appreciated!

-Matthew

Pictures of before/after some of the valves:

[95blkmax]

Just to make sure you got the simple stuff out the way, did you reset the computer? It could be that the cold-start parameters are still taking into account the prior nasty condition so now it's extra sensitive. Have you tried to see if by any chance there's a vacuum leak present after re-assembly? Try spraying brake parts cleaner around the gasket between the upper IM and the lower runner stacks. If the idle surges there's your ticket.

Great job on the valve cleaning btw! I gotta make the time to do that. But will likely wait until the cooler months. Heat index this week has been in the low-mid 100s here, screw that lol...