It sounds like it's running on two, or even one cylinder. It may be the ignition module, mine was more sensitive to moisture, probably because of cracked insulation. But it can also be just flooded, I remember starting Skoda 120 in winter and listening, as cylinders joined one by one (btw, that car needed depressed clutch, as the oil in transmission became too thick - but it didn't use wide range oil like Felicia) Have you tried to just disconnect the sensor? Iirc, ECU uses substitute value if the signal is out of range, which is still far from actual temp, but may be closer than whatever is sensor feeding now. FYI, you don't need to wait for pump every time, like with diesel glow plugs. The function is there just to prime the fuel lines and flush gas bubbles that could be there after long standing. Newer cars do that once you open driver's door. Once priming's done, you get full pressure almost immediately and if you want until the pump stops, it's the same as if you didn't wait at all, since the pump doesn't reactivate until you turn the key.