I just drove 2700 miles from Southern California to Washington state and back over the holidays.

While in snow country, my glow plug light refused to come on when I turned the key. After waiting 30 or more seconds, the car fired right up, but ran rough. The glow light also came on -- after I started the car, but went out after a minute or so. After the car warmed up, the engine smoothed out and cruised for hundreds of miles each day.

Upon my return, I discovered that the No. 4 plug was dead. New plug, problem gone.

Good luck.

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'91 300D 2.5 Turbo 330K
'00 VW TDI Golf, 190K
'67 BMW R50/2
'73 Norton Commando Interstate