Bonapartista

Gentlemen/Ladies,

my A8 3.7L has devised a plan to kill me. It developed a glitch on low throttle depression at low rpm it jerks a bit just at point where it's proper place for the speed. Uphill is even worst jerk. When I engage cruise control at say 90 kmh it jerks constantly at set speed. I went to mechanic who suspected MAF. He installed (I assume by his word) new Bosch MAF and cleaned throttle body. Now there's a new glitch where at times when I accelerate slowly let say at 5% throttle it goes like stink. Like I pressed 50% throttle. When it reaches let say 90 kmh i let go a throttle a bit to establish speed at that point it jerks. So MAF didn't solve nothing. After a couple of days of this, CEL lights up. After VCDS probe I get so many errors it's not even funny. First ABS light shows up, couple of moments later CEL comes up. What is funny, throttle resumes normal operation. Maybe I feel a hint of rough idle and a hint of sluggish acceleration. When I erase error in ABS, tranny and engine then I get jerkiness and sudden accelerations again also performance returns.

I should also say it's Zavoli LPG conversion. I don't notice any difference in behaviour if LPG is off or on. Also there were Lambda errors, when we replaced MAF they went away.

It's beyond me. Anyone had similar problems?


8 Faults Found:

17985 - Right Engine Mount Solenoid Valve (N145)
P1577 - 004 - Open Circuit
17535 - Fuel Trim; Bank 1 (Mult)
P1127 - 002 - System too Rich - Intermittent
16490 - Manifold / Barometric Pressure Sensor (G71) / (F96)
P0106 - 008 - Implausible Signal
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 -
16688 - Cylinder 4
P0304 - 001 - Misfire Detected
17537 - Fuel Trim; Bank 2 (Mult)
P1129 - 002 - System too Rich - Intermittent
16487 - Mass Air Flow Sensor (G70)
P0103 - 008 - Signal too High - MIL ON
18061 - Please check DTC Memory of ABS Controller
P1653 - 008 -

Readiness: 0000 1100

Jack88

Could have been an issue with the MAF wiring harness, the insulation can break down on those. Also, makes me wonder if there is any issue with the throttle itself. Check the basics, make sure your air intake isn't clogged up and filter is in good shape. If you want to test the MAF system, unplug it and if the issue disappears, you know that system still has a fault somewhere.

Bonapartista

Some update on the issue. I changed fuel filter, MAF sensor, all 8 coils, air filter, cleaned throttle body (took it out), no more CEL as before but jerk / jolt remains. When I accelerate let's say with 30% throttle and usually when I reach desired speed I let go throttle to match the speed. At that moment when speed of the car and throttle are matched then it jolts. It's not strong on light acceleration / load but when I go uphill it jolts so much you can kiss a windshield If you are not ready so it's load dependent. Also cruise control has same trouble with it. On small loads CC works fine but when I engage it uphill or on highway it starts to jolt repeatedly. Once it even started to jerk and jolt on highway at about 150 km/h it threw ABS light and it went into limp mode. I immediately stopped and turned off car. Started it again normal and continued ride without issues. I did avoid CC that day and don't use it over 130 anymore.

Any ideas where to continue?

dvs_dave

MP4.2+6.0

As dvs dave said, do a throttle body adaptation. And yes, suspect throttle body may be bad too, and then you can try cleaning the contacts inside. A few prior posts on that if you search.

Separately, look at your transmission computer/module for codes. I wonder if the jerking you describe could also be an issue with the lock up torque converter. Probably would focus on throttle body earlier though.

Jack88

I also was wondering about torque converter lock up issues or possibly clogged up solenoids or filter if the transmission has never been serviced.

Bonapartista

Thanks guys. Transmission is clear of any codes. It was never serviced. I do have oil and filter but it's too cold for me lying under the car right now. It will have to wait for spring. I did check in VCDS how lock up functions while driving. I noticed while you drive and establish constant speed and throttle it takes couple of seconds to lock up. That is normal operation. Mine jolts immediately when throttle aligns with engine speed. Much before lock up. That is my conclusion for now but is not out of the picture yet. I suspect engine issue here.

Throttle body is a good idea might be an issue, that is my next job on todo list.

I did an VCDS check on cam adjuster in group 93 (or 94 i'm not sure now) it shows 20° on bank 1 and 14° on bank 2 (driver/left side) while driving. I think I read somewhere anything under 16° (16 - 25° being normal) is a sign of adjuster binding / not going into proper position while driving. Idle is around 0°.

I did recently change cam adjuster on bank 1. Since then it runs a bit rough which is only noticeable over 2500 rpm. I guess bank 2 is also ready to rumble. I ordered mine at CS-Parts from Germany at 170€.

Slight warning regarding tool for cam adjuster. Mine came with the adjuster which broke before I even started to really screw on it. It's not made well, plastic was full of bubbles. Luckily I'm a cnc programer so I reverse engineered it and made it from aerospace grade aluminium. Now it will never ever brake.

When I find the time I will dismantle original cam adjuster to see inside what could be wrong with it. Might be fixable as OEM cam adjuster goes for 700€. There's at least 650€ pure profit.

pelletman

Transmission crossed my mind too

Bonapartista

I took advice from you guys. I checked transmission for codes. There were none. I changed oil in transmission per manufacturer instructions and maybe shifts improved a bit I'm not sure really. Jolting is still present.

As mentioned I changed Bank 2 cam adjuster and I started to get error on that bank P0012 Advanced setpoint not reached (Over retarded). Couple of days later I also change it on Bank 1 now I also get P0022 same over retarder error on this bank. Car starts rough when cold, hunting idle, sometimes even cuts off. There is white smoke alot too. SAI kicks in full speed which I never noticed before. Rattle is still present. I also changed engine oil to 0w30. Might be that both cam adjusters suck ***.

I find it strange if I start it cold and that rough start happens with SAI full speed and if I turn off car and start it again immediately there is no SAI and no huge amounts of white smoke.