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Master Auto Tech.
Master Auto Tech., A.S.E. Certified Master Technician
Category: VW
Satisfied Customers: 429
Experience:  Over 20 years working on imports and domestic cars
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I am a small shop with 20 years in the automotive field. I

Customer Question

I am a small shop with 20 years in the automotive field. I have a problem with a 2006 VW Passat 2.0 turbo that is just throwing me for a loop. It came in with the timing chain from the exhaust to intake camshaft broke. Removed the camshafts and performed a leak down test, all cylinders passed. Replaced the chain now the car has a surge while it is at idle. Drives great and has good power but you come to a light and you have to put it in neutral or you get whiplash for the surge. if you unplug the mass air and A/F sensor it will idle nice and smooth. Compression is 185 on all 4 cylinders, rechecked chain and belt timing. Watching data from my Autel Maxisys pro the timing will go from -15BTDC to +15ADTC, injection timing is 0.77ms to 1.55ms while the engine is surging. I am at a total loss here what the problem could be.
Submitted: 4 months ago.
Category: VW
Expert:  cloe0626 replied 4 months ago.

have you tried cleaning the mass air flow sensor

Customer: replied 4 months ago.
I have, did not change anything.
Expert:  Master Auto Tech. replied 4 months ago.
if you just unplug one of the sensors, does it still surge? Does it have to be both sensors? And have you checked for any air leaks? Spray carb or brake cleaner around? A hose left off?Just a thought.
Customer: replied 4 months ago.
If I just unplug one sensor the surge changes but it still continues It doesn't smooth out till both sensors are unplugged. There is no change if I unplug the MAP sensor, I smoked the intake and fixed 2 small leaks but that only slowed the surge a little. Also the PCV manifold is brand new also.
Expert:  Master Auto Tech. replied 4 months ago.
Did you unhook the battery when you changed the chain?
Also is the cel on?
Customer: replied 4 months ago.
the battery was removed when the chain was done. So far it has only set a P0300 pending but no CEL yet after around 20 miles of on and off driving.
Expert:  Master Auto Tech. replied 4 months ago.
I know you said it has a new pcv manifold but try this.recheck the pcv system. loosen the oil cap with the engine running. should be held in place by a slight vacuum. if it is overly difficult to remove, pcv is leaking somewhere.
also, loosen the oil cap (leave it installed, just setting on top of the filler neck) then free-rev the engine to near redline and immediately let off. watch the loosened oil cap while you do this. if the cap lifts off the filler neck at all, you have a pcv leak.
remove the dipstick when the engine running. if there is no change in idle, pcv leak. also make sure that little o-ring is still there under the dipstick handle.
also check the large plastic hose/line that goes from the block under the intake manifold to the pcv valve.
if the pcv is leaking, the car should idle poorly, misfire, but run decent above idle and driving.
Expert:  Master Auto Tech. replied 4 months ago.
Also, on the back of the valve cover is a hose that goes straight to the intake hose, there is a plastic one way check valve inside of this hose, check and make sure this one isn't missing. The reason why it could be running like a pcv problem is because of this missing valve so check the valve on the back of the valve cover.
Customer: replied 4 months ago.
Well I started engine and removed the oil cap, had a little bit of pull to it and when it came off the engine rpm's went up by 300 rpm, pulled dipstick and engine rpm's went up the same. Free-revved the engine with the oil cap loose and the cap did not move. With the cap off the engine surge is the same it just does it at a higher rpm. Checked hose from PCV to block and it looks good.
I looked at the back of the cam cover and see 2 hoses, a bigger one that goes from rubber to metal down to the top of the turbo inlet. The other is smaller covered in a heat shield goes down to the turbo housing, I do not see any check valves in them.
Expert:  Master Auto Tech. replied 4 months ago.
I was thinking it was in the rear of the valve cover. But maybe not. I just know it does go from the valve cover to the intake.
But all that being said, the unplugging the 2 sensors is odd. Usually when you unplug them and it gets better, esp the maf a known problem child on VW's, it means they are bad. I don't suppose you have ones losing around you can try swapping them out?
And are all grounds reattached?
That being said, has the owner commented on how it was running before the chain broke? Might this be an unrelated issue?
And finally if swapping those parts out doesn't fix it, and the owner swears it wasn't pre existing, I have seen really weird things happen to the programming in the computers when the battery is disconnected. It may need the ecm flashed.I had one, the owner brought in after the battery died and he replaced it. He had no reverse lights now. I went thru the diagnostics, found I could command them on with vag-com. Ended up the module programming corrupted by the battery dieing. Flashed it and all was good.Just a thought for you.Let me know what you think.Thanks
Sonny
Customer: replied 4 months ago.
This customer has been bringing the car to me for over 2 years and I know it has has lean codes in the past with the hard plastic cracking and splitting open so most of them are replaced but it has never surged like this before. Unplugging both sensors to make it run good is really throwing me off to. my thought is when they are unplugged the computer goes into a limp mode and that's what it runs good but I could be wrong. With my scanner I have a bluetooth J2534 box and can perform reprogramming, with that is there a mode in the computer to perform a idle relearn? There is a window on my scanner I can enter a mode # ***** the pcm.
Expert:  Master Auto Tech. replied 4 months ago.
Unfortunately I don't know the numbers. I know on my GENISYS I have to enter the numbers as well. But with vag-com it just pulls them up and gives the descriptions and doesn't give you the numbers either. :-/
Expert:  Master Auto Tech. replied 4 months ago.
If you want I can opt out and see if someone else can help with that tho?
Expert:  Master Auto Tech. replied 4 months ago.
Where you able to try reprogramming it? If so how did it do?

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