[s-cars] Go. No go. And; go.

[Brett Dikeman]

On Wed, Apr 8, 2009 at 11:07 AM, Bill Mahoney <wmahoney at disk.com> wrote:
> Maybe O2 sensor?

Motronic is open-loop during startup and for a few minutes until the
O2 sensor warms up.  Also, O2 sensors rarely go "bad"; their response
time just increases with contamination.  If the sensor was
disconnected or had a bad connection, you would see a check engine
light or have a fault code.

Aside from major fuel/ignition problems (ie coilpack failure, fuel
pump relay/pump failure, pressure regulator, etc)- what would affect
startup mixture and idle speed would be the ECU coolant temp sensor,
MAF sensor, idle stabilization valve, and...drumroll please...intake
system leak.  The ISV obviously wouldn't affect acceleration, but the
ECU temp sensor and MAF sensor sure would...and sudden stumbling under
acceleration.  Because of the ease of checking, it is worth it to
check the vacuum line to the FPR; if it fails or becomes disconnected,
the engine will run very rich at idle.  You'll also eventually get a
CEL on this, because the ECU will try to compensate for the rich
running.

Murphy's law is that it will be the pump if I say this, but- there are
a number of other things you need to be checking out before you commit
to a major job like replacing the fuel pump. At the very least, pull
codes using VAG-COM (blink codes don't cover intermittent fault codes)
*AND* check the first memory block to see if values are within norms
(but note that there are very specific conditions for the ranges given
in the Bentley- mostly around running time, coolant temp, battery
voltage.)

Start with the easiest stuff to test, even if the likelyhood is low.
If you need to do a boost pressure test, raid the tupperware drawer; 1
cup rubbermaid containers (the kind with the tan covers) are a
near-perfect fit for the hose off the MAF.  Just be REAL careful not
to over-pressurize the system more than .5 bar above normal boost
levels.

Really, your first stop should be here:
http://www.sjmautotechnik.com/trouble_shooting/20vboost.html

Brett