[s-cars] Fw: Still on 4 cylinders, some background.

[vonk]

----- Original Message ----- 
From: vonk 
To: AUDIJIM at aol.com 
Sent: Tuesday, December 20, 2005 11:16 PM
Subject: [acna_pcc] Still on 4 cylinders, some background.


Jim,
 
I know little about the 20 valve engine, but an experience with my ex-S4 may be relevant for you. 
 
Does your engine have an Engine Coolant Temperature (ECT) sensor that sends data to the ECU for warm-up mixture control? On my ex-S4 (Stage 3+), it contains two sensors. One for the Gauge and one for mixture control. The latter failed on my engine a while back, while the gauge indicated normally. This led to misfiring and much unnecessary parts swapping. If you have a similar failure this may be aggravated by seasonal temperature changes.
 
Have you switched to M1 0W-30 oil to eliminate the viscosity and lifter factors?
 
Might the roughness after a throttle blip indicate a problem with your throttle transient enrichment by either injecting too much or too little transient fuel?
 
Is your rough running getting worse with time? This might indicate a component failing gradually. In my experience, wiring failures, while frequently intermittent, are usually on or off, rather than better or worse by degree.
 
>From your report I get the feeling that you might want to look to mixture control as the prime suspect.
 
On the other hand, here's another possibility: If your intake manifold nuts are coming loose, or the gasket has sprung a leak, you may get extra air to one (#4) cylinder. The leak could close up more or less as the engine warms up and expands. This would be particularly noticeable at low RPMs and partial throttle. - Just a wild thought.
 
I trust you have a VAG tool and Lemmiwinks.
 
Don't do an engine/harness transplant just yet. :-)
 
Harald (vonk)