mountain lion
Veteran Member
The last 6 months I've noticed an intermittent stumble at idle only after lightly reving (after a small reverse or slow move forward especially) and it has been slowly getting worse/more frequent. The RPM drops down between 830-870 and the engine kinda chugs then jumps back up to 903 by itself. It first started only when engine was cool, but now seems to do it regardless of operating temp. Before we think worn out cam, see below:
2004 BEW - 258k miles
Installed at 238k miles:
Franko6 stage 2 cam (original cam still looked pretty darn good)
Bosio 1043 Nozzles (original pd100 injectors)
VNT-17
Darkside full SMIC upgrade kit
DieselGeek timing belt kit
RC 2.5 tune
Cam, nozzles and TB kit were all meticulously installed by a pro on this forum(with some assistance from me).
Things I've checked:
Lift pump is working properly
Tandem pump is the original LUK, but no leaks and car starts the instant the key is turned
No air bubbles seen in fuel return after injectors
Cam/lifters are basically new, but verified no signs of wear
Doubled checked injector connections and harness
Injector health is good: group 23 switch time deviation is around -25 to -30 on each. Group 13 injection deviation is all balanced to 0 and highest quantities are around +/- 0.30.
I had an oil analysis done back in February and everything checked out good, no fuel or excessive metals in the oil.
VCDS has no errors, MAF checks out ok, MAP and boost are good, coolant temp sensor seems to be working fine.
Timing is spot on based on TDC refence marks we put on the camshaft hub and cover after the job.
The torsion has been at -0.5 since the TB job and other upgrades. The last two weeks I decided to start adjusting it. First I went up to +0.5. Car lost FE and the rough idle got worse compared to -0.5. I went up to +1.5 and the idle was even worse there. Went the opposite direction and went down to -1.5. Things got a lot better here, but not perfect. Ended doing a lot of tests at .5 increments all the way down to -4.4. Car idled perfect at -4.4, but lost a LOT of low end. Went up to -3.4 and it also ran great. -2.5 is also pretty good. I've since settled at -2.9. FE is higher, but have lost some low end grunt (as expected). I would say it's pretty much running like a top here.
I'm at a loss as to what could have changed or be wrong at this point for the torsion to have to be adjusted. There were no issues for 16-17k miles since all the new upgrades were put in.
Is it possible the tandem pump has an issue? I did all the tests from the fuel system write up (except pressure readings), and everything pretty much checked out. I was able to pull a bit more fuel through with engine off but lift pump on (85ml instead of 25ml, but someone else had this exact amount on their bosch pump in that thread). There are no high RPM/load problems, car pulls strong all the way through.
I've checked everything I know, not sure if adjusting the torsion is the fix due to upgrades that have settle in or just masking another issue.
2004 BEW - 258k miles
Installed at 238k miles:
Franko6 stage 2 cam (original cam still looked pretty darn good)
Bosio 1043 Nozzles (original pd100 injectors)
VNT-17
Darkside full SMIC upgrade kit
DieselGeek timing belt kit
RC 2.5 tune
Cam, nozzles and TB kit were all meticulously installed by a pro on this forum(with some assistance from me).
Things I've checked:
Lift pump is working properly
Tandem pump is the original LUK, but no leaks and car starts the instant the key is turned
No air bubbles seen in fuel return after injectors
Cam/lifters are basically new, but verified no signs of wear
Doubled checked injector connections and harness
Injector health is good: group 23 switch time deviation is around -25 to -30 on each. Group 13 injection deviation is all balanced to 0 and highest quantities are around +/- 0.30.
I had an oil analysis done back in February and everything checked out good, no fuel or excessive metals in the oil.
VCDS has no errors, MAF checks out ok, MAP and boost are good, coolant temp sensor seems to be working fine.
Timing is spot on based on TDC refence marks we put on the camshaft hub and cover after the job.
The torsion has been at -0.5 since the TB job and other upgrades. The last two weeks I decided to start adjusting it. First I went up to +0.5. Car lost FE and the rough idle got worse compared to -0.5. I went up to +1.5 and the idle was even worse there. Went the opposite direction and went down to -1.5. Things got a lot better here, but not perfect. Ended doing a lot of tests at .5 increments all the way down to -4.4. Car idled perfect at -4.4, but lost a LOT of low end. Went up to -3.4 and it also ran great. -2.5 is also pretty good. I've since settled at -2.9. FE is higher, but have lost some low end grunt (as expected). I would say it's pretty much running like a top here.
I'm at a loss as to what could have changed or be wrong at this point for the torsion to have to be adjusted. There were no issues for 16-17k miles since all the new upgrades were put in.
Is it possible the tandem pump has an issue? I did all the tests from the fuel system write up (except pressure readings), and everything pretty much checked out. I was able to pull a bit more fuel through with engine off but lift pump on (85ml instead of 25ml, but someone else had this exact amount on their bosch pump in that thread). There are no high RPM/load problems, car pulls strong all the way through.
I've checked everything I know, not sure if adjusting the torsion is the fix due to upgrades that have settle in or just masking another issue.