Erratic throttle response when cold

[HPsauce]

Interesting, though not exactly the same as my symptoms, nonetheless very similar.
It all points to the F125 switch causing odd behaviour that doesn't throw an error.

One interesting test that you might be able to do is to set a cruise control speed at some point early in a journey (say about 35mph) and then when the symptoms appear at a lower speed turn cruise back on once at/over 25mph.
In my case this instantly (without moving my right foot) reinstated full power mode.

[Adrian E]

Just to add to that theory, there was a note on a service record for my S8 that the previous owner reported an unresponsive throttle.

Camspec didn't detect an issue during the time they had it for cambelt etc, but when I bought the car soon after I had the F125 flag up.

As I changed it pretty soon after first detecting it, it might explain why I never experienced the poor/non-existent throttle response to connect the potential causes of issues together?

[steamship]

Originally Posted by MikkiJayne

Interestingly, since having 'mended' my F125, mine is now doing this most of the time. The first 50% of the throttle does very little, but prod it a bit further and it takes off like a rocket. It happens mostly in 1st which is very annoying, but also randomly in other gears. If I'm in town pootling around at 30 and slow down for something it'll take a hefty prod to make it move, at which point it changes down to 2nd and goes a bit nuts. Its much better behaved in tiptronic, to the point I had to tow the FE home entirely in tip otherwise it would barely move. No codes either.

Time for a new switch methinks...

After I had the faulty F125 switch problem (dashboard lit up), I had it replaced with one from the forum sponsors. That has worked fine most of the time, but I too started experiencing the same issues as Andrew, and resolved it with the same quick stab on the pedal, although I only tend to experience it in the lower gears like moving off from junctions or having slowed at a roundabout.

Originally Posted by moltuae

Check your brake pedal switch too. Had a similar problem with mine a few years ago, turned out to be iffy brake pedal switch contacts. I noticed the fault would tend to occur more after firm braking and tapping/wiggling the brake pedal before setting off again seemed to alleviate it.

Curious you mention this as I've had error codes about the brake switch before and had it replaced with a brand new one. However, I still get error codes relating to the brake switch. In fact, I get it in Engine (01) 16995, Transmission (02) 17087 and ABS (03) 00526. Is it possible that the connector on the loom could be loose and not giving me 100% contact? If so, can the connector be opened up and the crimps tightened, although from memory I think they are round in shape.

[MikkiJayne]

Originally Posted by steamship

Curious you mention this as I've had error codes about the brake switch before and had it replaced with a brand new one. However, I still get error codes relating to the brake switch. In fact, I get it in Engine (01) 16995, Transmission (02) 17087 and ABS (03) 00526. Is it possible that the connector on the loom could be loose and not giving me 100% contact? If so, can the connector be opened up and the crimps tightened, although from memory I think they are round in shape.

Likewise. I've just changed the brake switch because all three modules were complaining about it. With the new switch only the ABS unit logs a fault. I wonder if that is still affecting the ECU?

Further diagnostics needed

[ainarssems]

I find that that error is always in ABS unless you press brake pedal after switching on ignition. So try that- switch ignition on, press and release brake, connect VCDS and scan ABS for fault codes, brake switch error should not be there.

[MikkiJayne]

Will do thanks

[Adrian E]

Originally Posted by ainarssems

I find that that error is always in ABS unless you press brake pedal after switching on ignition. So try that- switch ignition on, press and release brake, connect VCDS and scan ABS for fault codes, brake switch error should not be there.

That's weird - never had to do that with mine? Maybe it's a PF thing?

[HPsauce]

Originally Posted by ainarssems

I find that that error is always in ABS unless you press brake pedal after switching on ignition.

Yes, known idiosyncrasy.
(I think Ross-Tech have a note on it somewhere)

So try that- switch ignition on, press and release brake, connect VCDS and scan ABS for fault codes, brake switch error should not be there.

Standard procedure that I always use.

[MikkiJayne]

Originally Posted by Adrian E

That's weird - never had to do that with mine? Maybe it's a PF thing?

You might be right there - I've never noticed it on mine (FL) before the switch broke, but the Titanic (PF) did seem to behave like that even after a new switch. I'll try it in a bit

[MikkiJayne]

Mostly normal service resumed

When I fitted the replacement brake switch I got it in the perfectly wrong position (yes, there is such a thing!). It has two contacts - one normally open (for the brake lights), and one normally closed (for the ECUs). The ECUs expect to see both contacts change together so they know the switch is working. I'd managed to get it in just the wrong position so the normally open was open, but just enough pressure on it for the normally closed to also be open! The ECUs knew something was up so all got in a grump Wound the switch in another half turn and everything is fine now - no codes, and enough oomph from stationary to wake up the ESP I wish I'd figured this out before towing the FE home Steamship - that could well be your issue too?

Curiously the cruise control still isn't working, despite the ECU seeing all the switch contacts operating, which is odd. Need to do a bit more digging on that.

No brake switch error code on power-up either, so that must be a PF thing