2002 TDi Jetta wagon
This issue started the day before yesterday. I start the car. Everything seems fine. Go to drive and it's normal to ~2000rpm then the CEL goes on and there's no power. If you stay on the gas so it doesn't shift and wait for it to get to around 2800 rpm, suddenly boost kicks in and it takes off. After that it drives like normal until you shut it down.
Every time you start it, the same thing- starts fine, no CEL, seems fine. Then rev (under load, not neutral) to 2k, CEL turns on, stay on it to 2800, boost kicks in and it drives like normal until you shut it down.
The code it's throwing is P0101 (MAF-related stuff). I cleaned the MAF today, checked the air filter and checked my vacuum lines. Everything seems fine, though I didn't thoroughly check my vacuum lines with a vacuum gauge - just checked the turbo actuator and waste gate; both held vacuum.
I also don't think it's the MAF - we were out of town - I drove it 350 miles like this and it actually seems to be getting better mileage than normal, even though we climbed a 4200 foot mountain pass 3 times at 60mph with 4 adults, a baby, a 70 pound dog and rooftop box full of ski/overnight gear.
The most likely culprit in my mind is one of the little vacuum valves but does anyone have other ideas?
code?? im thinking under boost... like the vnt is stuck open and got lag... but codes will give a idea to what to look at..
So, I've been doing some more research and tinkering as well as discussing this on another site.
The problem is that the VNT is not closing until after an initial high-vacuum event. Why this is, I have yet to get to the bottom of.
When you start the car (whether it's cold, or already warmed up), there is no boost until you rev the engine to about 2600rpm. Then boost kicks in abruptly and will operate normally (building significant boost around 1900rpm and boosting smoothly as it usually does) until the engine is shut down and restarted. Every time the engine is started, it happens the same way.
The curious facts are:
- The only error code is the MAF code
- The car got the best mileage it has gotten since we've owned it while operating with this problem (unlikely that the MAF is actually bad)
- There's no "low boost" code, which is obviously the problem
- The problem arose during a trip that would have produced high EGT's on several occasions (a strange time for the VNT to begin sticking - see above)
I have done lots of research and will test all of the vacuum stuff as well as the VNT tomorrow, but it there anything that people think is more likely the culprit (things I should check first or add to the list)?
what i learned and how...
tap in a boost gauge to boost, also hook in vac gauge going to the vnt..
drive round and watch what the 2 do...
you could see when.how the vnt will hang up..
hell car was more drivable with lag vs limp.. but just unhooking the vnt was no solution as it will open up in a way it makes no boost unless reset by vac...