2000 A4 1.8T Quattro

This is the last act of a desperate man. I wish I had the free time to poke around my A4, but I'm just way too busy.

This started with just a lean fuel error code. (Stupid me, dropped $200 on a new OEM O2 sensor. Figured the aftermarket one the previous owner put in was just bad.) Then I noticed misfires when the boost was supposed to kick in. Months later, it’s worse. Drops into limp mode. Runs really rough in the rain; like its literally sucking in water somehow. Misfires like crazy in the morning when I first start up.

One other quirk I noticed: Idle speed sometime wavers (hunts) until I rev throttle and it settles.

I’ve looking all over for vacuum leaks and I’ve sprayed ether starter fluid everywhere. Haven’t tried the air compressor test yet. Found the EVAP check valve behind the air box had melted, but replacing it fixed nothing! Later, I tried hosing down the MAF sensor with cleaner, which also got me nothing. A bad coil pack wouldn’t explain why all four cylinders misfire. Crankcase breather hose looks OK from my angle. Sorry, don't have a boost gauge cause I'm not cool like that.

Bad diverter valve?
Bad EVAP leak pump?
Low fuel pressure / bad pump?
Or just simply a leaky hose I haven’t found yet?

Yes, its chipped. I’ll give it the air compressor test when I get a chance. Best suggestions appreciated.

Here are the engine errors from my jacked up VAG log:

Address 01: Engine Labels: None
Part No: 4B0 906 018 P
Component: 1.8L R4/5VT G 0008
Coding: 07201
Shop #: WSC 06335

9 Faults Found:
17536 - Fuel Trim; Bank 1 (Mult): System too Lean
P1128 - 35-00 - -
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-10 - - - Intermittent
16688 - Cylinder 4: Misfire Detected
P0304 - 35-10 - - - Intermittent
16686 - Cylinder 2: Misfire Detected
P0302 - 35-10 - - - Intermittent
16685 - Cylinder 1: Misfire Detected
P0301 - 35-10 - - - Intermittent
17956 - Boost Pressure Regulation Valve (N75): Open Circuit
P1548 - 35-10 - - - Intermittent
16687 - Cylinder 3: Misfire Detected
P0303 - 35-10 - - - Intermittent
17883 - EVAP Leak Detection Pump: Malfunction / No Signal
P1475 - 35-10 - - - Intermittent
16716 - Knock Sensor 2 (G66): Signal too Low
P0332 - 35-10 - - - Intermittent
Readiness: 0000 0000

 

Clear your codes. Then if the N75 comes back then replace it.

You've got one of three problems:
-You're overboosting - N75 can cause this. You could have a huge vacuum leak like the SAI hose.
-Your fuel system is not doing so well - weak fuel pump / bad FPR
-You're not too off on the AFM but your O2 sensor is good so this is probably the least likely. You could need to replace the MAF. You can try unplugging the MAF electrically to see if it helps.

 

OK. Took a look around the turbo inlet and didn't find any bad hoses. N75 valve checked out at 30ohms (presumed good). However, the connector on the wire harness looked a little sketchy. Contacts are clean, but the connector retaining clip is missing and there's some sort of oxide buildup on the outside of the seal. I'll try replacing that connector when I can find one. Reset the DTC and I'll post the new codes.

 

Cleaned out my DV, swapped out the N75 valve, replaced the vac lines, cleaned out the fuel pressure regulator, and then finally figured out it really was the MAF sensor.

Still, I'm not content because I'm getting flashing CEL misfires at high torque. Bad coils/plugs? Bad fuel injectors? Maybe this N75 or MAF is on the way out too? Fuel pump seems okay and doesn't make any noise. Otherwise, I'm happy to have most of my car back. I'll check which cylinders misfired later.

 

I think you still likely have a vacuum leak somewhere. But other than that, what gas are you using? Try Sea Foam. Have you replaced your plugs? Did you gap them correctly?

 

Is there the coil pack recall on 2000 a4s?