View Full Version : Slight surge 2,000-2,300RPM under light throttle

12-02-2012, 10:35 AM
2001 A4 Quattro 1.8T with 115,000
OK, first I have read every thread I could, and I think I have done just about everything suggested, pulling the vacuum and intake plumbing apart 4 times now, cleaned and replaced everything it seems, read below.
Continuing Symptom: Rough idle, worse at startup. Under light load, worse up slight incline, the RPMs will surge between 2,000 and 2,300RPM, a pulse feeling in power every 2-3 seconds. Strange thing is if you 'get on it' the engine runs right out, but move the throttle off and little and the turbo pressure drops out (I think, power drops like the tranny just shifted up, but it didn't)
First I replaced the MAFS, the upstream O2, Spark Plugs, Air cleaner and that crazy Vacuum Suction Pump valve. Vacuum lines were cracked also.
No Help.
Check COdes and it had the 17887 P1479-35-00 Vacuum Pump System Mechanical Failure.
Started check that and found that cheap convoluted intake hose was hard and cracked. and found more cracked lines.
No Help.
Kept going. New Diverter Valve, a Kayser upgrade.
No Help.
Pulled out the PCV, pressure control valve, Puck on the turbo intake line, cleaned and checked it. Even tried without it and the port plugged.
No Help
Kept reading and going. Cleaned the Throttle Body and replaced the fuel pressure regulator.
No Help
Pull off all the Crankcase Vent Valve and replaced it with its cracked plastic connector and tee hose connector.
Still no help.

Any other thoughts? Fuel pump? But wouldn't it have trouble under acceleration?
Last thought of mine is a wavering turbo wastegate valve or maybe repalcement of the entire K03 turbo assembly.

OK, no one has looked at this, so no help yet. I got a pressure gauge attached to the intake, removed the Puck valve and plug the intake. Remove the 'Y' Pump Check valve and plugged that, taking all vacuum leaks out of the equation. Drove the car and watch the gauge. There is an extreme fluctuation in the manifold pressure when the surge and bounce occurs. light acceleration, boost comes in 6-8 psi then drops to 0 then back up. During the RPM bounce 2-2,300, the pressure bounces also.
Got to be the Waste Gate or Turbo or Both, RIGHT?