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View Full Version : Surging/Hesitation at Partial Throttle (TDi)



Chris_J
22-07-2008, 01:22 PM
Hi everyone.

I've just recently purchased a VW Golf 1.9 GT TDi 115 (AJM) second hand with 112K miles on the clock. The engine runs really sweetly and I am totally chuffed with the car. I've never owned a TDi (or any diesel for that matter), so I'm completely new to the game. Before the Golf, I was an avid VW Polo fan, and I've just sold my beloved supercharged G40!

I'm enjoying the Golf, as it feels much more solid and is an absolute dream to drive, but I have one relatively minor niggle which I've just noticed, that I need to get sorted.

The problem occurs in any gear, but is more obvious in the lower gears. Basically, at a specific throttle position, the car will sort of hesitate or surge as if I was gently increasing and decreasing the throttle position, at a frequency of about once a second.

With the window wound down, I can hear the turbo spool up and down when the problem is happening. It will only do it in a certain throttle position, which is at about 1/8th.

After a bit of experimenting, there are two ways in which you can stop it. Either slighly increase the throttle and the turbo will spool up fully and pull away as normal, or you can let it do its thing, then after about 5 seconds it stops the hesitation.

There are no other problems I can detect, i.e the turbo pulls very strong throughout the rev range, in an gear. It's almost like the turbo isn't sure whether it should spool up when I feather on the throttle!

I've just got hold of a VAG-COM, which I'm going to look at tonight and I've just done a full service, which included air filter and fuel filter, but the surging still remains. As I mention, these engines are completly new to me, so I'm hoping someone can shed a bit of light and give me some clues as to where I should start investigating.

Thanks in advance guys.
Chris.

adzul
22-07-2008, 08:30 PM
I had a similar problem with a fiat jtd engine i used to run.

the problem I found was an inconstant output from the MAF (mass airflow meter) measures the density of air post airfilter. the ecu uses maf reading to control fueling. Fueling is fluctuating or stalling because MAF output is off kilter.

if you have a laptop can you isolate the maf output signal and see if it's inconstant?

good luck :biglaugh:

'zul

mluton
22-07-2008, 08:37 PM
I was going to say MAF also.

Welcome to the forum

Chris_J
22-07-2008, 10:01 PM
Cheers guys.

Tried to get it hooked up to VAG-COM tonight, but I'm having issues with it.

So you're both saying MAF, is there any way to test the MAF (eg. unplugging?) and if the readings are inconsistent, is it a case of replacing it, or can it be cleaned?

Thanks for your help.

adzul
23-07-2008, 10:25 AM
In theroy it can be cleaned but you'll not get it as good as new.
If you want to try cleaning it look at;
http://www.fiatforum.com/punto-guides/129316-1-9-jtd-maf-sensor-cleaning-replacement.html
A new one is a good idea (unless u r skint like the rest of us :biglaugh:)
Find your maf in the car (plastic unit in air line post airfilter) write down all the codes on it and start with a famous auction site. DON'T be tempted by the cheap chinese made ones - they don't last 5 mins. Bosch all the way.

'zul

Chris_J
23-07-2008, 09:39 PM
Thanks adzul.

I'm on to Ross-Tech at the moment to sort out this damn VAG-COM, so I'm going to see if any codes have been thrown first.

I'll have a look over all hoses and vacuum pipes to see if I can find any air leaks. Any idea where the wastgate acuator sits?

Chris_J
24-07-2008, 10:55 PM
Thanks for all the help guys. Turned out to be a malfunctioning EGR. I removed nd plugged the vac hose, which has cured the problem.

Cheers!