UK-POLOS.NET - THE VW Polo Forum

Hi,
I am driving my gti for exactly a year now. It hasn't let me down so far but I do have some issues.
My shifter is moving backwards and forwards in 4th gear when press and release the gaspedal. Ive read about this but a solution was never mentioned. Also the engine has some hickups when accelerating. Especially when accelerating somewhat slowly. I replaced the throttle body, ignition coil, cables and spark plugs. No errors in the ECU and all sensors read normally when monitoring the ecu. I also replaced small vacuum hoses between inlet and fuel pressure regulator, they were in bad shape. Ive read about this problem quite a few times on the internet but no solutions mentioned. Next thing to do is analyse the fuel pressure.
Han

Welcome Han

Change the fuel filter - that causes alot of issues like this

The shifter movement is often due to worn bushes on the shift cables - check for damage and repair/replace them

I forgot to mention that; I also replaced the filter.

Interestingly, when the car starts shaking/stuttering, I directly lift my foot of the gas and then press it again and away is the shaking... But it can return a second or two/three later.
Sometimes the car drives perfectly for the entire trip to my work (20 miles), no stuttering, loads of power. So I don't think it's something mechanical like a bad valve, but most of the times the stuttering is there, sometimes very slightly, sometimes a lot.

Another problem is that my xenon lights don't calibrate when turned on. The mechanism is mechanically intact. I have reasons to believe that this function is deliberately disabled, but I don't know where to look. Cabling and fuses seem to be intact. As a result my lights are aiming to low.

(forgot to mention it's mileage: 125.000)

Check the brake servo hose from the throttle body. These have a habit of splitting.

As for the xenons. The car doesn't auto calibrate like more modern cars when the lights are turned on the first time

It's possible the mechanism has seized under the car - it's on the rear axle.

You ideally need to run a basic settings then adaptation on the xenons using VCDS which should get you back into the home position to adjust them properly

Ok I have found the sensor on the axle. It looks okay but there could be a problem internally. I found a procedure to set the home position for the xenon lights. If I follow the procedure then the lights should aim at the right angle again. The auto-levelling function doesn't have to work.

I replaced the sport muffler with an ordinary SDI one. The engine sounds quiet now.

The car will be serviced within two weeks. I will let them check for vacuum leaks and perform fuel pressure check. They can put a sensor in between the fuel lines and read it while driving. Hoping it will shed some light on the cause of the engine troubles.

Thanks all so far,
Han

The home position is more to learn where the demons should be for adjustment purposes. You may find it doesn't move the headlights at all and they'll need to be manually adjusted

I manually adjusted the headlights. The auto levelling function doesn't work, but it's not required to work here.
I can get a used levelling sensor, maybe I will try to fix one day.

I have replaced the MAP sensor to try and fix the jerking engine. It doesn't make a difference. I cleaned the camshaft sensor. I installed another and clean throttle body, new spark plugs, leads and bobine. Replaced vacuum hoses as well. Temperature sensor replaced and fuel filter.

There's not much I can try anymore. The timing belt should be ok ; otherwise it would jerk all the time. Mechanically the engine should be ok, at times the car runs just great.

I'm going to replace the battery as well as I know that it's old and weak. I saw some ground connections underneath the battery tray so I'll give them a cleanup as well. This could be useful since I seem to have grounding issues. 2 weeks ago my turn lights kept continuously burning (made one of the reflector caps melt) when locking the car and a week ago another ghost, I drove off and noticed the blower not working and turn signals were dead as well (turning engine off and on again fixed this).

I get strange O2 sensor voltage readings. Can anyone confirm that the pre-cat oxygen sensor is a wideband sensor?

What readings are you getting?

I can't really say, my EOBD reader stopped working. I remember pre-cat signal being rock steady. Post-cat sensor signal was mostly steady at 0.7v but did fluctuate sometimes.

I would be interested in the STFT values when the engine starts jerking. Then I can see whether the lambda control is cutting off fuel or enriching fuel. Maybe it doesn't do a thing at all when it's jerking and all seems fine, now that would be really weird.

I'll first try to get the EOBD reader working again.

Got a working OBD2 reader again.
The readings are clear, the short time fuel trim stays between 0-3%. When the juddering starts the stft goes negative with values dropping to -11%.
So it's the lambda control playing up. I can't think of a reason why it would do that other than a sensor issue, wiring or ground issue. But why only on slight acceleration? Why not during a steady speed? No idea.

Thats a bit strange indeed

Check the wiring on the lambda thats in the manifold in front of the gearbox. It often breaks down/gets damaged and causes all sorts of issues

Yes I know. There is no connector near the sensor, just wiring with bends and curves (wiring seems too long) and some tape around it halfway. By looking at it I'd say the sensor may have been replaced in the past.
I'm at a workshop tomorrow for refilling my ac system. I'll ask them to take a look at the wiring. It will be easier with the car up.