Thread: Td5 higher than normal revs with auto in P

Hello Paul,
Mine has always done this if I blip the throttle normal tick over. I know it shouldn't do this but have got used to it.
Ian

I have seen this in a mates d2. I thought it was related to all the heavy duty clutch packs and torque converter he had fitted. Interesting issue. I can't think what would do it unless the xyz switch is worn out?

One of the microswitches in the XYZ switch seemed to have a broken return spring, but was opening the switch contacts when fully depressed. The shifter position seems to be correct and the indicators display correct position immediately after you select a different position.

There is good chance that the Neutral/Park switch is intermittently faulty given the iffy microswitch. I haven't been able to see a delay with the nanocom, but the 1 second sampling interval and the fact it only displays on off makes it less than ideal for finding electrical issues. I'll have to check it with the multimeter when the weather becomes a bit less nasty.

I've bought a good xyz switch off ebay, as the xyz switch housing has been broken in the recent past. I had the auto rebuilt in early jan 2014 so you can connect the dots on that one...

cheers
Paul

I think I've narrowed it down. Today is a lot cooler than it has been so I had switched off the Aircon. When I hooked up the Nanocom to see if I could find anything unusual the engine wouldn't go into high idle.

I was going to pack it in but I realised that the Aircon had been running on previous occasions. So I switched the Aircon back on and tried the D -> P move again and the engine instantly dropped into high idle. To triple check I switched Aircon off again, and I couldn't trigger the high idle behaviour.

Now it is just a matter of working out why this is happening.

Water over the switch?

The old V8s had a fixed idle compensation for aircon on.

I notice on a TD5 that they also must have idle compensation as the revs stay similar Aircon on or off.

Perhaps your aircon is low in gas and the compressor is not giving the calculated resistance and the revs are increasing.

This would only be the case if the idle compensation jump is a fixed one and the ECU does not automatically seek the target idle revs.

You are probably the best person to know whether the idle compensation is fixed or variable.

Regards Philip A

I haven't looked at the AC compensation tbh. I did trace the AC clutch request line through to the Microcontroller and know what flags get set internally. I'll have to look at the code and see if that tells me anything.

I did a bit more testing in an attempt to work out what the heck is going on.

If I turn the A/C on with the selector at P or N the idle behaves normally, but if I then shift to R or D and back to P or N the rev's hit 960-970. So it seems to be the transition between gears which is the trigger.

There is no indication I can get from the Switches sections of any of the Nanocom modules that would implicate the position switch, but I keep getting drawn back to the conclusion that it is the cause of the problem.

I'll have to pull the centre console trim off later in the week and check with the multimeter to see if that reveals anything more.

cheers
Paul

I always thought that the engine computer would compensate revs when the A/C is turned on so the idle stays at the right RPM based on a request from the BCU. So when i fitted a 2nd A/C Compressor for compressed air on my TD5 engine i thought it would get upset and sputter and when it is switched on. The REVS don't visually or audibly drop at all. The car computer doesn't know about my 2nd A/C unit so it must have another way of keeping the idle at the right revs.