olikoli

Hey everyone,
I need a bit of expert help from all of you experts.
I have a 2005 4.2L, and as of lately I have a rough idle at start with the big clunking when starting.

I have read many threads and posts but I just cannot be 100% sure what it is. Some people are saying that engine in my car does not suffer from carbon buildup and some are saying that it is.

I would like to try a seafoam treatment, but I am not sure if this will help or not. Should I feed it through the vacuum lines, add it to the oil, add it to the gas tank, or should I not even bother on this engine?

Car has 190K KM, and I have recently replaced sparkplugs, oil, air filter and fuel filter.

Any input is highly appreciated.

KnappAttack

The "clunking" your hearing is the timing chains rattling upon startup. tensioners are hyd. and they bleed down when the engine is off. Mine has been doing this since I had 50,000 miles on. Still doing it with 182,000 miles on, Has not changed.

I run a whole can of SeaFoam thru a full tank of fuel maybe twice a year just to keep fuel system clean, does nothing for the chain rattle at startup.

The 05 4.2 DOES NOT suffer from the dreaded "carbon buildup" that the FSI engines do, so no worry there. Only a condition of the directed injected FSI.

olikoli

Great to hear that carbon buildup is not an issue. I guess I will run the seafoam through the gas tank. Maybe it could help a little with a gas consumption. I've noticed a poor consumption as of lately...

squidix9

I'm not a fan of magic goo, with the exception of fuel system cleaner and specifically for my 4.2. Occasionally I remember to throw a bottle in one of the other vehicles and rarely do I see a difference. However with the A6 I try to do it more regularly and I feel it helps. I don't use any particular brand. If I forget it starts to rumble and will occasionally stumble at idle. After dumping cleaner in it tends to smooth out.

ProtoFly

I'm of the opinion that all of the NON-FSI 4.2's with the chain system will eventually need a complete timing chain/tensioner/adjuster service.

Kevin Gary, one of the most fastidious when it comes to keeping his car serviced via Audi, has his car in for this now. (Waiting for him to post what the outcome is).

The timing chain guides are made of a type of plastic, and eventually crack, giving the infamous 'rattle' on startup.

In my case, the passenger side upper adjuster shed its plastic into the exhaust cam sprocket, which skipped a tooth. Just getting done with a valve job and timing service now, should be back on the road within a week or two.

It's not a trivial service, as the engine has to come out for this, but if your car is otherwise running OK, better to do this pre-emptively than to wait for a failure, as a failure means bent valves and much more expense.

Note that the FSI 4.2's have been redesigned with respect to the cam adjusters and tensioners, and I've not seen timing chain failures on those engines yet - only the carbon buildup, which is pretty common to FSI.

raj99

The fact is everything degrades over time...metal fatigues, rocks turn to sand, and plastic crack... However, to call out pre-emptively removing the engine and changing the guides, is also not necessarily the best course of action. Not only is at a huge expense to remove the engine, but what if after removal your guides are in perfect shape and have no issues?

I agree that should the guides fail it could cause valve damage, however the guides are not designed to fail. BTW, I'm not saying they don't crack/disintegrate either. I think this one is a subjective matter at best and obviously Audi didn't design the car to have these guides replaced as part of their maintenance schedule, but I, like the rest of you, have read enough about such failures.

I for one will not be pulling my engine to put in new guides...if or when they do fail, I think it will be time for me to evaluate either getting a C8 (hopefully...based upon timing) or a Tesla.

newa6er

what is a CB?

raj99

Carbon Building

or are you referring to what I wrote 'C8' - which I simply assumed would be the next designation of the Audi A6 platform

newa6er

C8, I should wear my reading glasses

OP, I would do a VAG COM reading and see what the engine measuring blocks 93 value looks like, the clunking at start from a lazy tensioner or a stretched chain may not be so bad, but combined with a rough idle, could indicate a problem, or they could be two separate issues

olikoli

I did complete scan with WAG COM last night but saw no issues at all.
I will have to do what you are suggesting (measuring blocks) and see if anything shows up.
Would it not give me some kind of error when I do complete scan if something is wrong with "measuring blocks?