I have a 2000 Audi A6 with a 2.7 (150,000 miles) which has recently began to run pretty rough (enough that car shakes at idle). It does not kill and only smokes a little at startup after sitting for hours although the exhaust does have a rich smell to it all the time. It only bringing up one code. P0300 Random Multiple misfire. It was brought to a import mechanic which did test the ignition and said it was good. He also checked the fuel system and replaced an injector and filter which has not fixed the problem. I have been doing a little research on this site. Seems as though the MAF is a common problem on these cars but don't see them causing the problem that I have. I also want to do a pressure check on the intake but am not sure how to go about doing this.

Any ideas on where to start with this one?

 

Misfires tells me it could be bad plugs or coils. The mechanic should have picked up on that. I suppose the MAF could make it run rich. Let us know what you find out.

Are you on your OEM turbos? That's a lot of miles if you are, and good to know for the rest of us 2.7T owners.

 

It's a random misfire though. If it were specific coils wouldn't it specify a specific cylinder misfiring?
I recently purchased the car so have no idea if it's the original turbos or not as well as any other maintenance done to the car.

 

You need to do a cylinder balance test to see if its really on multiple cylinder or not. This can be accomplished by checking value blocks 14,15,16 for misfires or unpluging injectors with the engine running to see if it misfires worse or no change. That will help identify what cylinders are misfiring to isolate the cause. You can unplug the maf to see if it is causing the rough idle. If the idle smooths out with the maf unplugged then its a maf issue. Also check for vacuum leaks.

 

Not sure it is a coil thouhg it is a popular cause of misfires.
MAF as said above, or vacuum leak. Also, could it be one of the coil amplifiers?

 

MAF.

 

Unplug the MAF & see if it runs better, if so, then it's the MAF.

If not, I would replace the CTS.

 

It can also be the ignition control modules. Had the same thing happening to me and ended up replacing those since I had just changed the coil packs and sparkplugs.

 

We had it happen (running rough at startup, cylinder missfire) on our A6 2.8. The dealer did and injector cleaning (perhaps the MAF got cleaned too, but I doubt it) and it has been fine since.

 

I worked on it for a few hours yesterday.

I unpluged the MAF and it actually ran a little worse so I gurss that rules that out.

I checked all over for vacuumn leaks and found none even while spraying carb cleaner all over.

By disconnecting ignition coils I determined cylinders 2 and 5 (center cylinders 1 each bank) to be missing. I tried swapping coils and spark plugs with a "good" cylinder but found the miss to remain at 2 and 5.

I then checked the injectors which also ssem to have a good pulse and identical ohm readings.

A little bit of oil seems to be building up in the cylinders but I have never seen a little oil keep a car from running on those cylinders. Plus like I said earlier in the forum, there is no blue smoke but it does have a rich raw fuel smell.

oh, compression on these two cylinders measures 130.

I am running out of ideas.