The temp sender and thermostat were not long ago new and behave as expected (I have observed the values in VCDS as the car warms up and the engine is shut off, the fan comes on, etc.) Spark plugs are also recently replaced and are Bosch super 4's (and AFAIK are the correct type and gap.) Throttle body cleaned and adapted, and have put some redex injector cleaner in the tank. No error codes in VCDS. I had a test done for combustion gasses in the coolant which was negative, but have not had a hot compression test done, and oil level does not fall. It takes noticeably much more turning start, in fact sometimes I end up releasing the key leaving the engine not running, usually the engine starts quite quickly on the second attempt (which would tend to make me think fuel supply/flooding). Other than that once it has started it seems to run well.

If it is not due to lack of compression the only things I can think (in order of probably best suck it and see tests) are maybe the the fuel filter (there's a chance it's the original one with the car) MAP sensor, coil pack, or the fuel rail pressure regulator.

Would getting the engine warm and disconnecting the MAP sensor and seeing if it starts or runs any differently tell me anything about whether that is the culprit?

Another thought I had was to try super unleaded fuel as that would be less prone to detonation (not that I know this is what is making starting slow though). Any thoughts? TIA,

Edited 20 August, 201015 yr by anewman

Mine did that - Lummox fixed it - I'll send him along in a bit to tell you how

Thanks MissP, would be handy to know what caused it on yours.

I have hooked up VCDS again and worked through the measuring blocks as described in the Skoda fuel injection service manual for the AQW engine. Everything appears to be within nominal values, and there are 0 misfires detected after running the engine a while.

The ignition angle relief shown under measuring blocks 020 were all at 0 degrees BTDC. The nominal values quoted are 0 - 15, and the service manual only makes issue if one cylinder deviates or values are above 15. Blipping the throttle doesn't make the values change.

Edited 22 August, 201015 yr by anewman

i would suggest that the valve clearances are too tight, but the mpi has hydraulic followers doesn't it?

Yes, and apparently the basic settings are maintenance free.

missp's was a temp sensor.

Is it a two pin grey sensor?

does it make any difference if you just simply unlug the coolant sensor?? just because the readings are within range doesn;t mean it's the right reading..

Yes replaced the temp sender with a grey 2 pin one (was a febi which I believe are the OE MFR's). Will try unplug it next time - am I looking to see if it is any harder to start than with it plugged in?

no, it should start easier with it unplugged, when the coolant sensor is open circuit (unplugged) the ecu subtiitutes the signal for a generic value for a hot engine

Starts sweet as pie with the temp sender disconnected.

I had noticed when I replaced the temp sender and thermostat that it stayed a notch below the centre mark at all times. I mistakenly assumed this was Jorily's Mk2 thermostat running slightly cooler than the standard one. I didn't think such a small variation in readings would make the engine more difficult to start. Will get a new temp sender and it seems that should sort me out. How stupid of me to rule out something as it was a new part.

Thanks for the replies guys

Changed the temp sender and no change in coolant temp display on dash (just to left of centre), and no more than a slight improvement on starting when warm. Based on the fact that blue coolant was introduced to the G12 at some point (not by me but a garage previous owner went to), and even though I have flushed it previously and used a chemical flush, and that there is some sludgy stuff evident above the water line in the header tank - I am giving the system a seriously good flushing and cleaning through in the hope this improves it. If not I will accept the longer cranking time needed as just the way the car is so long as it starts The other unusual thing is the coolant still rises fast as soon as the fan cuts in and overflows if the cap is removed (almost like a water fountain). I am not sure if this could be due to a blockage by sludge. However the system does not overheat in any way.

Edited 21 September, 201015 yr by anewman

I had a problem with the thermo it may be a sign if you have a slight rattle it has been known the pump is on its way out

Still occurs after a seriously good flush and reverse flush of radiator and engine block plus new thermostat and temp sender. Will next look at the MAP sensor which I understand measures temperature somehow. As disconnecting the temp sender sorts it out I suspect it must be related to temperature. Never failed to start, just takes longer.

Water pump seems to be operating fine.