Hi!

My Fabia has performed very reliably to this day, it has almost 415000 kilometers in its metre. It has now got this strange problem somewhere, and I've run out of ideas with it.

While driving, if I lift the gas pedal up, the engine doesn't start engine braking. Instead the RPM stays where it is, or starts to slowly decrease. When it has come down enough, the RPM starts to bounce a little and the car begins to do kind of pumping motion. Basically I have to just put the gear to neutral and brake only with the pedal.

What makes it really strange, it does this only with 3rd and 4th gear. With 5th and 2nd gear the engine braking is working fine. It does it most of the time with 3rd and 4th, but not always.

I have OBD cable home, so I tried to look at the fault codes with VAG-COM. It didn't find anything...

Ideas?

throttle position sensor?

Okay so I tried to diagnose the problem by removing the throttle position sensors cord which was going to the throttle flap. The car seemed to lose some of its power so I guess it went to some kind of limp mode. But the same problem still existed. Could the problem be caused by the MAP sensor?

Worth a chance http://www.briskoda.net/forums/topic/244178-simple-cheap-diy-tune-up-brilliant/

DB.

Anti stall kicking in? Above reset might do it. Please let everybody know when you find the answer.

Is this car an automatic or manual?

When were the injectors last replaced/overhauled?

Okay I tried the above reset, did not change a thing. I also tried the throttle position adaptation to where I found instructions from vag-coms website. However vag-com just said that group 060 is not available.

Its a 5-speed manual. And the injectors have never been replaced.

Throttle body adaption process is for petrol cars. The V157 manifold flap is not really an electronic throttle body and does usually throw a fault code when faulty. Check that you have 12V between pins 1 and 4, when the ignition is on.

It is the fuel quantity injected that primarily determines engine speed, as diesel burns in an excess of air. Under normal operation the manifold flap is open. It closes to slow/stop the engine.

Does the car shudder to a stop when you turn off the ignition?

The common factor for 1st, 2nd and 5th gear is that you would be at a relatively low throttle setting.

First check the mechanical fixing for the accelerator pedal position sender and the pedal. If this is loose, it can give the same symptoms as you see. This would not throw a fault code as the electrical parts would be working OK. You can check the opeation of the sender by reading MB2.

The injectors will be well passed their best at 418k kilometers (260k miles) and will probably need new nozzles. If in injector was sticking open, it would not throw a fault code.

The N146 fuel metering adjuster in the pump determines the amount of fuel injected. If this was sticking it could cause this problem but it does usually throw a fault code.

The engine is stopping just fine. I'll check the pedal later today, I'm currently at work.

Is there any way of checking the injectors before replacing them?

By the way, the problem started back in the winter, when I took the car from -25 degrees Celsius to a warm place for a CV joint replace.

Sry I've been quite busy lately. Anyway, I checked the gas pedal. It seems to be mounted well. Also VAG-COM reports it's position correctly.

I've forgot to mention that when I take the gas fully off while driving, it doesn't start lowering the RPM. However if I press the gas pedal just a tiny bit, it starts coming down just fine and the RPM goes down to certain point, depending on the throttle.

Okay. I've got a suggestion this is caused by a transmission problem, since the third and the fourth gear are apparently situated in the same axle.

As it's a manual transmission, I can't see this being a factor. When you press on the clutch, do the revs drop to zero?

Yeah, the revs drop to zero.

Recheck to be sure we heard correctly.

1. The RPM stays up (no engine braking effect) if you simply release the pedal

2 If you nudge the pedal the RPM drops to idling speed (about 950)

3 If you release the pedal, but then push in the clutch the RPM drops to idle although you haven't touched the throttle again.

Is this right?

What happens if you touch the brake?

Do you have cruise control fitted?

Can you post the line from the VCDS that has the engine details e.g. 1.8L 5V 110KW TLG V005

I did a little video showing the problem better. You can find it on:

do have cruise control fitted, it works fine on 5th gear but disengages itself immediately on 4th and 3rd.

Ill post the engine details when I get from work.

I did a little video showing the problem better. You can find it on:

do have cruise control fitted, it works fine on 5th gear but disengages itself immediately on 4th and 3rd.

Ill post the engine details when I get from work.

You have a problem with the cruise control. The only reason I asked for the engine details was to see if there is a 'G' in the text (which means that cruise is enabled in the ECU).

If you switch off the cruise control with the slide switch, do you still have the problem?

It doesnt disappear with the slide switch. Ive also tried to disable the cruise control with VAG-COM. I'll check the cruise control connections, will post back after that.

Edited 3 August, 201213 yr by tmn

IIRC, the login code to deactivate cruise control is 16167. The 'G' in the engine code string will disappear when cruise is deactivated.

All those points indicate the cruise control interfering with the engine speed. Can you disable it?

Hi again!

I disabled the cruise control with VAG-COM (the G disappeared from the engine line) and set the cruise control switch to off-position. The problem however still remains. Could the cruise control interfere with the ECU as the physical wiring is still there?

I would unplug the cable from the cruise switch as a start. A short in the wiring could affect the ECU. I have seen a different problem caused by a short in the preinstalled part of the loom on an Octavia TDI (it didn't have the stalk or stalk loom fitted).

I tried disconnecting the cruise control switch from the ECU. However it didn't help :(

Oh dear, sounds like the integrated cruise control programme has affected the "normal" instruction set. Can you borrow another ECU to check?

Worth trying another complete depower now you've disconnected the wiring.. Take off battery leads and join them together, leave 2 hours and retry.

Fingers crossed for you.

Its evening now, so I'll take them off and leave for the night. Lets hope for the best. Ill post the results on the morning.