322,000 mile 2006 engine stalling when coming to a stop. Very hard to start. P0101

Bought the car last week and just drove it home this afternoon. When cold it started and ran fine. Drove 20 miles home on the highway no problem. I do hear a hissing or whining noise when accelerating. Not a turbo whine. When I got off the highway the engine stalled as I come to a stop. I was able to get it get back in gear to pop the clutch and restart before coming to a full stop. Held the rpm at 1,000 while using the hand brake to stop. Noticed this happening a few times again but caught in time. Stopped off at a store for 10 minutes before getting home, after which it was very hard to start. Got home and turned it off and tried to restart. Ok if done immediately, but after 10 minutes very hard. Vagcom shows P0101 MAF sensor G70 implausible signal. Not getting a check engine light. My last TDI was a 99 over 10 years ago so I’ve been out of the game a while. My limited searching here has led to cam wear or EGR valve problems. Where do I start to diagnose this?

Sounds like EGR valve stuck open.


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So what is it about the EGR valve being open that it's hard to start when hot but not when cold?

Possibly in-tank fuel pump? Make sure you hear it run for some seconds at key on. You could also confirm fuel flow by pulling input line at filter.

RE: EGR - check other thread here. I believe you can disable and lock open to confirm.

kdawg89 said:

Sounds like EGR valve stuck open.

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Removed EGR valve and it was closed. Bench tested it. Works fine.

atikovi said:

Removed EGR valve and it was closed. Bench tested it. Works fine.

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Did you look at the intake while at it?

P0101 is open/short to ground so maybe the MAF is not getting power or the wire to ecm (pin 5 IIRC) is broken/grounded.
Does it behave better with the MAF unplugged?

I once had a very small leak in a fuel hose (just sweating) that caused the fuel to retract back to the fuel tank between runs and that made it hard to start. But that was an older diesel and the lift pump should negate that. Should...

Have you done the basics. Replace fuel filter and air filter. If your hearing a hiss then leak test the pressure pipes from the turbo. Will need to pull valve cover to look for lobe wear on cam. Like another poster stated pull maf plug, if it is a bad maf it should run better. Pull line from tank at fuel fuel filter to check flow when key is first turned on. Lots of DIY on these issues which are most common. Keep in mind wiring harness issues(shorts) can also be a problem and poor grounds. Check where wires cross etc.

nokivasara said:

Did you look at the intake while at it?
P0101 is open/short to ground so maybe the MAF is not getting power or the wire to ecm (pin 5 IIRC) is broken/grounded.
Does it behave better with the MAF unplugged?

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Vagcom shows MAF output but I'll try unplugging and see how it runs.

James & Son said:

Have you done the basics. Replace fuel filter and air filter. If your hearing a hiss then leak test the pressure pipes from the turbo. Will need to pull valve cover to look for lobe wear on cam. Like another poster stated pull maf plug, if it is a bad maf it should run better. Pull line from tank at fuel fuel filter to check flow when key is first turned on.

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Air filter is new. Car ran fine on the highway so the fuel filter should be OK. Just ordered an intake hose bladder adapter thingy for my smoke machine to do a leak test. Checking the cam is on the list.

The hissing noise is likely the EGR cooler leaking, which they all eventually do. I have seen some really bad ones, but they never caused the engine to quit running, but I guess it is possible.

I also know that there are some additives that people can overdose the fuel on, and cause this exact same thing.

No EGR cooler.

Disconnected the MAF sensor. No change. Engine dies if I press the clutch down and take my foot off the accelerator when it's warmed up. Talked to the previous owner and the cam was changed at each timing belt change, the last one being about 100K ago. Guess I'll pull the valve cover next. Do the cams only last 100K on these?

Stepped on the gas...err accelerator for the first time. This thing is quick. Plenty of boost. I think that hissing noise is more like a squeal and it's from the serpentine belt tensioner. Pulley bearing is worn. Replacing it tomorrow. BTW, is there some way to rev the engine from under the hood?

Engine doesn't die anymore when I come to a stop. Not sure what I did to cure that other than clean the MAF sensor, but it still throws a code for that. Still hard to start when warm but I have some ideas.

Now, as of yesterday, the car starts just fine when it's warm. Not that I'm disappointed, but makes me a little nervous when a car fixes itself for no apparent reason. Yesterday I also got the CEL for the first time for same MAF sensor code as before. Why was there a code before, without the CEL on?

My car did the same thing. It was the EGR valve. The hissing is likely the EGR cooler shaft leaking. If it has been removed, then maybe a gasket. To diagnose the EGR valve, the best way is to use VCDS and cause it to cycle using the measuring blocks feature. However, on mine, I removed it, then used VCDS. I watched it cycle in my hand. Mine was not closing all the way. It was variable opening, but it never closed. So, when I replaced it, the MAF P0101 code went away.