Hi everyone,

 

I have a slightly irritating issue that has been ongoing for a few months now. Having driven this car for several years, normally its idle RPM is 800. However, for several months, the car is having intermittent periods of high idle at 1000 RPM and at times the idle can be slightly rough. The car has no fault codes on my Autel machine.

 

The DPF values before and after the latest regeneration that happened this Tuesday were:

• Before Latest Regeneration
  • Km Since Last Regeneration - 417.1Km
  • Soot Mass Measured - 0.21g
  • Soot Mass Calculated - 24.26g
  • Oil Ash Volume - 55.3341711g
  • Oil Ash Mass - 55.3341711g
  • Ash Load Limit - 70g

• After Latest Regeneration
  • Km Since Last Regeneration - 2.5Km
  • Soot Mass Measured - -5.57g
  • Soot Mass Calculated - 4.68g
  • Oil Ash Volume - 55.3402682g
  • Oil Ash Mass - 55.3352631g
  • Ash Load - 70g

 

When the car initiated this particular regeneration, a grumbling sound came from the engine bay which I had never heard before but it has not happened since.

 

Having done some research, I am suspecting one of the following:

• Bad DPF differential pressure sensor/blocked DPF - unlikely as the DPF is regenerating every 415Km or so which I believe is fine
• Bad alternator - unlikely as there is no battery warning light and the voltage of the battery during idle is 14.5V
• Weak battery - again unlikely as there is no battery warning light
• Fuel injector issue - unlikely as there are no engine fault codes and the car is not misfiring
• Bad thermostat - unlikely as I fitted a new OEM thermostat from Audi in Nov 2023
• Bad coolant temp. sensor - possible as it has not been changed, over the past week when motorway driving, the temp. gauge on the dash was fluctuating between 70 and 90C instead of staying at its usual 90C 

Also, over the past week or so, there has been an extra sound coming from the engine bay (I believe it is loudest on the offside of the car) that is louder on accelerating, not sure if this is related. This video of me testing the DPF differential pressure signal wire contains the sound of the engine on idle and while it is revving on idle (https://drive.google.com/file/d/1SfIBwlzODhr4Rjy9tdwqpNCoTVE_anyY/view?usp=drive_link).

What are your thoughts as to what could be causing these issues? Any help would be much appreciated!

For those experiencing the same problem as described above, turns out the above symptoms were caused by bad coolant temperature sensors!

To summarise, the symptoms I was experiencing were:

• Intermittent high idle of 1000RPM rather than the usual 800
• Rough idle when the coolant temp gauge on the dash was 70+ C
• Temp gauge on the dash fluctuating between 70C and 90C (normally the temp stays at 90C once at temp)

Remember to buy new OEM sensors if changing, otherwise your problem may not be fixed.

Thanks for letting us know.