Changed the glow plugs, ones came out had VW stamped on them, replaced with Bosch long life ones(£10 each).

Now with the cold mornings the heater light only stays on for about 1 second, start car and it struggles, seems like misfire, if i turn the key 2-3 times and start, its starts ok.....

is the relay on its way out or is that normal, can i test them whilst in the engine ?

kevin