Surging 4kq

["Doyt W. Echelberger" <Doyt@NWOhio.com>]

Running out of things to try for fixing the surging.

1986 4kcsq accelerates fine and runs strong above 40 mph, but when I try to
drive at 25 mph in 2d or 3d, for maybe 200 yards, the engine acts like it
is getting a variable supply of air and fuel, and even seems to cut out for
maybe a 10th of a second now and then.

I call this surging. The surge cycles last about a second and then it runs
smooth maybe 3 seconds, and surges again, in a seemingly random manner.
Sometimes the surges are so strong you could call it bucking, makes the
slack in the drive train very obvious, clanking.

My mechanic ran electronic tests on all the components of the engine
management system. It has a new O2 sensor. We swapped parts from
smooth-running engines (altitude sensor, air intake potentiometer, fuel
distributor, associated parts). We replaced molded vacuum hoses and found
and fixed several vacuum leaks. We switched distributor caps, replaced the
spark plugs, adjusted the CO, and ran it for two weeks on Techron and then
removed all the injectors and tested the spray patterns.

All these adjustments improved the condition slightly, and now the bucking
is unusual and the surging is less alarming, but basically there up to
about 40 mph. I think it is there above 40 but it just gets overwhelmed by
the momentum of the car.

My mechanic is calling in the services of a district CW consultant next
week, but I thought that maybe someone on the list would have had a similar
problem and be able to help me look at the solutions through the microscope
of experience.

In the back of my mind I suspect a leaking cold start injector that
dribbles fuel into the system in a random way, but that is only a wild
guess. And I am so inexperienced in this engine tuning thing that I KNOW I
don't have a chance at doing this alone. And my mechanic is out of ideas.
He drives a 1986 5kT that looks like a new car, and he really digs Audis
and cares about having happy customers, but he has gone through his bag of
tricks on this problem.

Could this be something associated with the carbon cannister or the air
filter or the air intake tubing or some other exotic part of the
environmental/clean air gadgets?

Help.

Doyt Echelberger