RPM fluctations when car is idle Audi A4 2011 1

[mgaspersic]

Hi guys,

I have been searching for a while on this forum for any usefull informations about my problem, but I can't find anything. I hope someone could help me. I have big problems with RPM fluctations when car is idle. While car is driving everything seems to work fine, fluctations only occur when car is idle.

Here is video of my problem:

https://www.youtube.com/watch?v=5kMfWYH-tmA

If I add more power to engine, it's running ok and also there are no fluctations when I drive car OR even there are no noticable fluctations when car have more than 1200 RPM. Also none of any strange sounds can be heard from engine. When car is idle, rpm fluctates from 700-1000 rpm also even more if I turn on A/C like 600-1000. Fluctations have similar feeling like car would run out of gas, but it don't stops. I'm sure, there is/was enough gas inside. When problem occured, car had almost half of a tank.

Car has also been tested with VAG-PC software and report was:

Address 01: Engine Labels: 03L-906-019-CAG.clb
Control Module Part Number: 03L 906 019 AL HW: 03L 906 019 AL
Component and/or Version: R4 2,0L EDC H34 9097
Software Coding: 0A194012232403080000
Work Shop Code: WSC 06324 000 00000
ASAM Dataset: EV_ECM20TDI03L906019AL A02008 (AU48)
VCID: 75E5E5E76701
4 Faults Found:

4698 - Function Restriction due to Received Malfunction Value
U1113 00 [032] - Open or Short to Plus
4699 - Function Restriction due to Received Malfunction Value
U1113 00 [032] - Open Circuit
5175 - Fuel Pressure Regulation: Regulation Discrepancy
P1065 00 [109] - Short to Ground
Freeze Frame:
Fault Status: 00000001
Fault Priority: 2
Fault Frequency: 2
Mileage: 160206 km
Date: 2014.11.26
Time: 17:17:55

4278 - Implausible Data Received from ABS Control Module
U0415 00 [032] - Short to Plus

Readiness: 0 0 0 0 0

Probably only third message is related to this problem (Fuel Pressure Regulation). There is also a date and time described and matches the time when I notice error.

I am not sure what's going on and error message which vag displayed to me is to much general to me to locate the problem.

What could cause rpm fluctations in my case? Is it safe to drive with fluctations? is it possible to damage engine? I know, that there could be number of parts which could fail, but I don't know where to start. I don't want to drive car to audi servis yet.

Car is Audi A4 2011 TDI B8 88kw 120hp, engine type is CAGC, 160.000 km.

Mgaspersic

 

[gruntguru]

It is probably safe to drive.
It is unlikely that engine damage will result.
I was about to suggest a whole list of checks then noticed its a TDI - different ballgame. This is unlikely to be an engine mechanical fault (which is where I would start if it was a spark ignition engine). The fuel pressure code is a big clue and I would be starting there. Monitor the fuel pressure sensor output(sorry I don't know the type to recommend how to do this but probably a voltage or frequency to measure) and confirm that fuel pressure is fluctuating when the problem occurs. Fuel (rail) pressure will directly affect injected quantity and therefore idle speed on a CRDI system.

Engineering is the art of creating things you need, from things you can get.

 

[mgaspersic]

Thanks for your replay gruntguru. Is there any possibility that it's actually an pressure sensor fault? What are other components that might fail aswell and should be checked? Also I forgot to mention, that in a car dashboard I don't see any warning light which could indicate, that there is anything wrong with car or engine.

 

[BrianPetersen]

The various "open or short to plus", "open circuit", and "short to ground" comments present in the diagnostic output suggest that the problem is electrical in nature. The "function restriction" codes are secondary but the "fuel pressure regulation" followed by the P1065 "short to ground" is the primary one. I would check the wiring from the ECU to the rail pressure regulator (which is on the fuel pump attached to the engine). But ... Did anyone ever unplug something while the engine was running?

Also, when is the last time the fuel filter was changed?

If you see significant metal flakes in the fuel filter housing when you change the fuel filter, your high-pressure pump (HPFP) may be on its last legs. The shrapnel may have contaminated the rail pressure regulator valve, but that's only an indicator of impending pump destruction. This shouldn't give the "short to ground" codes, though.

 

[mgaspersic]

It was failed fuel rail pressure sensor. He should produce from 280-320 bar of preassure but after some measurement we figured out that he was producing more than 500 bar of pressure. After replacing unit, car starts to work normaly.

Thanks for any help!