engine is bucking when a/c is on

[Kneale Brownson]

At 12:24 PM 07/16/2003 -0500, Gordy_Schesel at allianzlife.com wrote:
>I thought it was fuel with an insufficient octane level at first.  Engine
>bucking occurs only once in a while in the higher gears but only when the
>a/c system is operating.  This has happened previously when wife put in
>regular gas without thinking.  I have always used premium Amoco gasoline.
>Is this a timing (timing belt is 40k miles old) issue?
>
>tia
>91 200 20v tq 108k miles
>91 100 quattro 196k miles

There is a known problem of the magnetic clutch on the A/C causing a shock
to the ECU.  It's described on Scott Mockry's
website:  http://www.sjmautotechnik.com/   A frequent additional symptom of
this problem is that the radio makes a "pop" noise (if it's turned on) at
the same time the engine coughs.    Bernie Benz has a 10-cent fix that
involves soldering something onto the A/C relay.  Audi's fix is $150 for a
revised relay and an insert into the wiring harness to the A/C clutch that
adds a diode to the wiring.