low power at low rpm

jamieson32 · April 29th, 2012, 18:58

Hello all,

I'm looking for some insight into a low power problem that I have been experiencing over the past couple weeks. I have done extensive searching and reading over the past week and have come across multiple possibilities and am looking for some expert opinions.

My car is a 2002 Jetta TDI with 265 000km, sprint 520 nozzles and a TD Tuning stage 3 tune.

The car recently threw a P1556 code (Charge pressure control negative deviation) and the symptoms are as follows:

The car can cruise at high speeds on the highway but the acceleration is very slow compared to normal.

When accelerating from a stop 1st gear is pretty gutless compared to normal, 2nd is gutless until ~2700rpm and then the car really takes off. If you keep accelerating the power remains strong in 3rd and 4th gear.

I sometimes experience low power issues when driving normally in (the car isnt always strong in 3rd and 4th... but it is strong more often than it is slow).

Thanks, and I'm looking forward to hearing some opinions.

Wingnut · April 29th, 2012, 19:01

Could be a bad MAF? You should try to hook up with someone with a Vag-com and check to see if its working properly.

Seatman · April 29th, 2012, 19:02

I'd go for a leaking vacuum pipe myself, had a similar thing with my car recently where the turbo wouldn't kick in till late and it was a leaking vac pipe. The vnt relies on vacuum in order to create boost.

BuzzKen · April 29th, 2012, 19:07

vacuum hoses, vane actuator or n75 valve.

jamieson32 · April 29th, 2012, 19:50

Thanks for all the replies. I am out of town this week but will try to get the maf logged when I get back. If the maf checks out to be fine, I will start looking into vacuum leaks.
Keep the opinions coming, I appreciate the help.

Seatman · April 29th, 2012, 20:25

"2nd is gutless until ~2700rpm and then the car really takes off"

That line makes me think it's not the maf, usually when the maf goes it has no power up the revs, just a short burst low down but nothing above 3000rpm.

"The car recently threw a P1556 code (Charge pressure control negative deviation)"

I also haven't seen that code with a bad maf, I suspect with a bad maf reading the ecu doesn't know whether or not the boost is low or high. The most common ones for low boost are a leaking vac line or a leaking boost pipe.

MoldovaDIZEL · April 29th, 2012, 23:20

n75 i think

OmegaRenegade · April 30th, 2012, 07:23

start with checking the vacuum lines - you might have a line that has come disconnected. Make sure they are all connected, then run your MAF test. From there N75 and vacuum line (make sure they're not leaking)

Wingnut · April 30th, 2012, 07:53

The vacuum leak is a good suggestion. The first place to look is the brake booster hose. It is the thick tube that goes from the vacuum pump to the brake booster. It is made of hard plastic and can crack. Usually it splits right at the joint:

This is the part:

This is what happens (very common):

Toronto_Vento · April 30th, 2012, 11:56

I have been chasing some strange driving behaviour in my 01 Jetta for a while (no time to dig and figure things out). I did end replacing the turbo actuator which helped things out for a while, but ultimately didn't solve the problem. (the old one was so rusty that it rattled internally when I took it off) About a week ago, my car was getting fairly gutless. Got home and discovered that the tube I had installed years ago for my boost gauge had rubbed through and was allowing pressure to escape.
The car is suddenly much smoother and gets way better mileage. (VNT vanes are still sticky, but that will be solved at a later date)