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55k on the clock. Full service history. All filters regularly changed.
Problem has existed for 3 years. Local Nuts & Bolts garages have tried to fix several times, so have changed plugs, leads, distributor and Cap twice
Starting problem occurs when cold and hot and luke warm engine
Sometimes it will start first time, next time you have to crank the engine for 20-30 seconds, and pump accelerator - it always starts, but when it does there is a large amount of blue smoke
When finally started the engine runs sweetly, pulls good, good acceleration. Stop the engine, and it probably will not start without cranking a long time.
The engine does not burn any oil.
At last MOT, it started OK, passed emissions test, engine was switched off by garage and then they could not start it again. I had to show them to crank it for 30 seconds, it then started. They plugged into their laptop but could find no error code
I have tried different keys, in case a problem with one.
I guess its a sensor of some sorts or ECU or maybe even the immobiliser, but all this is beyond me
Disconnecting the battery, I feel sometimes improves the starting, but not for long
Problem as said is both when cold, luke warm and hot. Sometimes it will start first time other times not
Any ideas Thanks

Message from Paj for info to other Polo owners
I had the car in the VW Main dealers, Peter Cooper in Portsmouth.
They checked the ECU for any error codes and found none
They checked valve and ignition timing and all was OK
They too, then couldn't get the car started
They found it was the Engine Temperature Sensor that was giving completely wrong temperature readings to the ECU
At ambient temperate if was giving a reading on -2degC, so the ECU was providing a very rich mixture regardless of what the actual engine temperature was.
Sensor was changed £32 for the Sensor, I had to pay Main dealer labour charges, but it was well worth it.
Car now starts first time every time

Thanks for providing this useful information

I was going to say, looks like the temp sensor is playing up. This can cause all kinds of problems with starting, fuel efficiency and emissions too.