JayA64.2

Can someone please provide guidance -

2005 Audi A6 4.2, 90K

Was gone out of country for 4 months April 2015 - Aug 2015
Upon returning the oil pressure sensor valve went bad got it replaced along with the oil filter and oil change
Car has had some unusual Vibrations on idle for the past several years but just a few weeks ago the vibrations got very severe.
Now CIL flashes at idle, stays on when driving.
Don't feel much difference in the pick up, but feels like the fuel efficiency might have dropped.

Changing out the spark plugs has taken care of misfire code for cly 5, 6.
However still have the random misfire code P0300.

Need help, one of the member suggested sea foam on a different thread.

Has anyone had similar issues, how was it handled?

FL C6.5 Avant

What is the detailed mx history of your car?
What is VCDS telling you (not just generic OBD-ii scanner)?

Have all 8 coil pax been recently replaced? that is a stab in the dark without knowing anything beyond what you said.

JayA64.2

I just had it re-scanned - Misfire on Cyl 5, 6, 7 & 8 and multiple misfire code.

No i have never replaced the ignition coils. The existing coils by visual inspection looked just like the brand new coils when compared. However when the spark plugs were removed I found just a little bit of oil on the threads of the spark plugs. Is that ok?

I am confused as to what to do next.

audi bug

Around 2010, there was ignition coil TSB.
My 3.2L coils were replaced by Audi dealer.
I am guessing 4.2 V8 was affected to.
You may contact Audi dealer and check open TSB for your car and service history for coil replacement.

JayA64.2

Thank you i will look into it tomorrow.

JayA64.2

So I checked with the dealer and the ignition coils were replaced in 2010. They are just 30K old and look brand new.
Also the head gasket, catalytic converter were replaced a few years ago.
Can you please recommend which fuel system cleaner to use - Chevron techron, Lucas oil deep clean or the one that's sold by Audi?

audi bug

Doesn't sound like a healthy engine.
Techron is recommended, but I highly doubt that will do anything for misfires.

JayA64.2

I use to have an extended warranty so everytime I took my car to the dealer, service center ended up replacing something. I really haven't had any issues for the last 2 to 2.5 yrs. Just the misfires now.
Will add 1.5 bottles of techron tomorrow and see if it helps.
I think moisture + carbon built-up + bad fuel are the 3 causes.
If there are any other suggestions please drop a message. I want to do the right thing, but save money at the same time.

terak0306

1. Check fuel rail pressure for that side of the engine. Cylinders listed are all on one cam I believe.

2. Check fuel filter. My 2008 a year ago was giving me all sorts of random codes. All it ended up needing was a new filter.

3. Check battery. Bad voltage can give you all sorts of issues.

4. I would be suspect of the cam timing, tensioner, and adjuster for that cam. Could be something as simple as bad oil quality, clogged oil line, or worse....something mechanical with engine timing.