Couple of rev surges on startup today

[jimbof]

Twice when I've started the car today and put it in reverse to manoever the revs have surged up to about 1100rpm - both times my foot well away from the go pedal - and then died down again after coming out of reverse promptly. Can I replicate it now? Can I £@(£!. I should add, no fault codes logged.

Any ideas? I changed the coolant bottle / cap the other day, but other than that nothing has changed recently.

[whitep]

Is it a high miler? You havent got oil leaking through the system have you? My old octavia used to do that and occasionally it used to do it while I was driving. I realised that it was very close to runaway because the oil seals on the Turbo were shot. Take an intercooler pipe off from somewhere and see is there is oil in the airway.

[jimbof]

I wondered about that, weird that shifting back to neutral seemed to snap it back out of it though.

It has got 143K on it now, still on the original turbo. No fault codes logged either.

The intercooler pipes have always had a liberal dose of oily crud on them - I thought this was quite normal on these cars? I've never looked inside.

[jimbof]

Think I know what caused this - twice in the last week now I've had the Emissions Workshop message up. Both times it has been 17664/P1256 - Engine Coolant Temperature Circuit (G62): Open / Short to B+.

From Rosstech:

"Starting the engine when engine is warmish or warm, idle rpm immediately is 1200-3000rpm".

Oh well, another thing to add to the list...!

[whitep]

Oh that's a good one. At least it's not a potential popped engine!!!

[jimbof]

Changed out the coolant temperature sensor yesterday, which has cured my occasional surge on startup and the "emissions workshop", which was now coming on every other trip.

 

The sensor fitted was the original (so about 11 years / 149K miles old) - and interestingly enough it looks like there might have been coolant passing the o-ring and then entering the back of the sensor.  It was quite scaly, not sure if that is usual?  I wonder if this could be my slow coolant leak (which hasn't gone away after changing the expansion vessel / cap)

 

I must admit I found it quite tricky to get to - I think it is worse on automatics as there is the added bulk of the EGR cooler and all it's associated pipework, which you don't have on a manual.  I ended up taking out the airbox (disconnecting the MAF) which gave me much more room - without this I think it is probably impossible.

 

I wasn't agile enough to prevent the car losing quite a bit of coolant in the process - must admit I wasn't quite prepared for the torrent!  So I let it go, retrieved the old o-ring and inserted the new sensor and o-ring in a calm fashion.  Bled the system of all air through the bleed hole in the top of the heater matrix hose and topped up with a bit over a litre of the purple stuff.  Washed down the driveway and underside of the car to prevent any of the local wildlife getting poorly.

 

Quite pleased with myself for having sorted it

[oh_superb]

Well done mate! On the V6 TDI it is a 2 min job as the sensor sits vertically inside the vee.

[jimbof]

So the V6 isn't all bad, then... :-p

[rotodiesel]

If you chop open your failed sender, you'll find it packed with rock-hard white epoxy. The thermistor elements (there are two of them) are brittle and fracture due to unmatched coefficients of thermal expansion causing fatigue when cycled.

 

The later green-bodied senders have a soft encapsulent.

 

Moronic design - for the last 15 years at least...

 

VAG - putting the customer----------------somewhere.

 

rotodiesel.

[Gaz]

So the V6 isn't all bad, then... :-p

 

White man speak with forked tongue! :p   

 

Gaz