Fault finding rough idle / start up

[JonofHove]

I rode my 45,500 mile 2012 GS to work and I noticed the exhaust popped a little more on the overrun than usual.

Went to ride home and it would not start. Key in, turn and nothing.

Tried the next day and managed to get the instrument / neutral light on.

It did not give the EWS warning or anything else unusual.

Tried to start and it went CLACK and then dead.

Tried jumping it with my car and leads - same again.

Next day I tried starting and it will now run but is rough and the throttle response once revved and released seems slow to react to idle again.

Battery was new in mid 2025, terminal secure and good voltage.

I thought it could be ignition coils but anything else to check / look at please?

Thank you.

 

[iangough]

Possible fuel blockage or fuel pump maybe ? Old fuel also

 

[Slipperyeel]

How long have you had the bike? Is it new to you?

 

[Joca]

I'd check the battery date first. It could be an old one...

 

[GORILA]

It sounds like one of your ignition coils is breaking down. If you have a GS911 you can plot their running performance to see if one is failed.
Another thing to check is that the battery terminals are properly tightened down. Put a torx bit on them and make sure they are properly tightened.

 

[Steptoe]

It sounds like one of your ignition coils is breaking down. If you have a GS911 you can plot their running performance to see if one is failed.
Another thing to check is that the battery terminals are properly tightened down. Put a torx bit on them and make sure they are properly tightened.

Very easy to check the stick coils. Takes 5 minutes and no diagnostic equipment needed.
Disconnect both lower/secindary coil sticks where the leads plug into the stick (saved removing plastic guards) .
Fire up the engine and see if it runs on both main coils sticks. Obviously you’ll notice if only one side is firing.
If ok reconnect the lower secondary coils and disconnect the main coil sticks, again where the leads plug in (saves removing plastic guards) .
Fire up the engine and see if it runs on both lower secondary plugs.

Obviously the ones that don’t fire have failed . Thought I’d best state the obvious as there have been a few members recently who have missed the obvious and taken umbrage when it’s been pointed out

 

[JonofHove]

Thank you for the advice:

I've owned it for 5 years, it had fresh fuel in it. When it did start it turned over strongly like a healthy battery does, it was not labouring.

It started at work, ran a little rough at idle then sounded ok. So I rode it home, it was exhaust popping whenever the throttle was being closed in 3rd, 2nd and 1st.

I'll start with checking the coils as per Steptoes directions and report back.

 

[Steptoe]

Also make sure the TPS is firmly located in place.

 

[JonofHove]

Also make sure the TPS is firmly located in place.

Thanks mate - will do.

 

[theoneandonly]

if nothing works , organise a BBQ for Saturday or Sunday .

 

[Pukmeister]

Also check the throttle cables are seated properly, both at the throttle body housings and inside the plastic cable splitter box beneath the fuel tank LHS.

 

[botus]

you keyed on next day, no electrics = wiring / battery

other running fun as others say maybe fuel pressure, atomisation and aging coils

the extra pop from the exhaust - remove check clean flap valve - I have a 10 k mile looks like brand new 2011 GSA - the flap valve started to stick last year - the design is not fit for purpose, with gunk specifically able to build up around its recessed budget bearings - if you are aware that gunk is really an acidic water with particulates of carbonised dinosaurs its never going to end well

 

[JonofHove]

Thank you for your inputs everyone. I followed up all the suggested causes as per instructions above and there is an intermittent failure of the lower right hand side coil. I have ordered a full set from Autodoc (delivered overnight) and will swap them over the weekend. I'll start with the faulty one, head out for a ride to ensure that this confirms my diagnosis before swapping out the others.

I've also ordered a new throttle position sensor from Motorworks as it was the original and not expensive to swap at £40.

I'll report back once completed.

 

[JonofHove]

you keyed on next day, no electrics = wiring / battery

other running fun as others say maybe fuel pressure, atomisation and aging coils

the extra pop from the exhaust - remove check clean flap valve - I have a 10 k mile looks like brand new 2011 GSA - the flap valve started to stick last year - the design is not fit for purpose, with gunk specifically able to build up around its recessed budget bearings - if you are aware that gunk is really an acidic water with particulates of carbonised dinosaurs its never going to end well

Thanks, I removed the flap + cables and fitted a short section after it kept sticking.

 

[Santa-2512]

Thank you for your inputs everyone. I followed up all the suggested causes as per instructions above and there is an intermittent failure of the lower right hand side coil. I have ordered a full set from Autodoc (delivered overnight) and will swap them over the weekend. I'll start with the faulty one, head out for a ride to ensure that this confirms my diagnosis before swapping out the others.

I've also ordered a new throttle position sensor from Motorworks as it was the original and not expensive to swap at £40.

I'll report back once completed.

TPS is an easy fix - unplug, unbolt & remove, replacement is the reverse

 

[JonofHove]

The replacement throttle position sensor supplied is marked Delphi SS10562 in case anyone else is looking for one, they're available around twenty quid online.

Will test ride over the weekend when temperatures decrease.

 

[botus]

then you wipe the adaptions (within the engine management) and build a new set (as it says In BMW documentation) or the new TPS will likely make it run far worse....

there is quite some variability in any of these sensors - the bike remembers a smidge of throttle on the old one meant it needs x fuel on tiny throttle openings and adapted to suit, the next sensor can be wildly different at these tiny throttle applications and say 20k miles of tweaks are completely mad for the next sensor and they need to go in the skip urgently

check poor instructions - leading you believe its just plug and play at the bottom of this part

Yet - further down in the section you never read as you thought it was plug and play - Follow up work - and the key bit most don't understand / never complete