A4 Avant 2.5 TDI need help. Engine Problems and things i've tried.

[Tyrah]

Hi guys, i hope you have some insights that might help me

Car: A4 Avant B7 2.5 TDI BDG Multitronic 230k KM

• Changed the gearbox oil around 40k km. The car had the wrong oil in the gearbox, and it wasn't filled up properly, this solved the "grinding" in winter, when just started the car. No issues with the gearbox since.
• Changed the timing belt around 30k ago.
• Had the timing set using VCDS.
• IQ values are not that far off (don't have VCDS at the moment to post new values)

Car behaviour:

• Car starts fine, cold or hot, maybe turns for about 1 extra second if sitting for only few hours.
• When it starts it gives a big puff of smoke (pretty big)
• After 10-15 seconds, the car starts rough idling, shaking.
• On idle it usually starts puffing smoke. And there is a very pungent stingy smell. (a lot actually)
• Revving it slowly, when cold cold (0 degrees celsius outside, and car just started) it revs smoothly up until 2k (will stop here as from here on is smooth).
• When the car heats up a bit, revving it again from idle to 2k(in neutral), the car starts shaking and hesitating between 1400 and 1600 rpm,, then it's smooth. (usually u can feel this badly if riding in sport mode at around that rpm, the car shakes pretty violently (not always). You can feel this shakes even if riding on cruise control at 100km/h the rpm is in the above range then.
• When the car gets to around 80 Celsius, the car idles smoothly, but still smokes (white) if let for a few minutes and smells bad.
• There is no black smoke on hard acceleration.
• Flooring it from full stop shows the boost values on torque to about 20-21 and then drop to like 18 while still accelerating.

Things i've tried:

• Disconnecting MAF. (no change to rough idle).
• Put a resistor instead of the signal from injector (no change).
• Disconnected the coolant sensor
  • Car started running smooth. No more rough idle.
  • Less smoke on start.
  • Unless driven like a granny, no smoke on idle, and the smell is almost completely gone.
  • Get a bit less mpg. (maybe around 0.5-1.5 L/100km).
  • I don't feel the car to be more sluggish. Seems to pull good. There is maybe a small difference on the way the car changes gears in sport or seems to be revving a bit more in drive.
  • I've put a new CTS in and all the previous issues are back.

Conclusion: Only disconnecting the CTS made the car run so much better. New sensor didn't fix the issues.

Also, the coolant reservoir is cracked (i bought a new one, will change it soon) so i always have the coolant level maybe 5 mm under the minimum.
When i removed the CTS, no coolant leaked, i could see it being on the bottom though.

Please advise, what should i try/do next. I want to get rid of the rough idle, and smoke + smell. I'm killing my fellow drivers at stoplights...

 

[NHN]

I would try temp replacing the CTS wiring & see what occurs.

 

[Tyrah]

I would try temp replacing the CTS wiring & see what occurs.

I see, but if the wiring would be faulty, wouldn't i see any DCT codes? Looking in with ELM and torque, i can see the temp readings, and they seem to be correct, but then again is something i could try...

 

[NHN]

If things improve when sensor disconnected & new one doesn't fix, then next stop is the wiring imho.

It's not unknown to have wiring issue without an error, but logic suggests an error should show, but it's hard to diagnose over the net.