I have a 1991 350sd turbo diesel [no bent rods ---yet---] my car starts up quite normally with glow plug lamp functioning ok then goes out---sometimes it will come on again---after i'm in motion---stay on about 30 seconds then go out. doesn't do this every time---wonder whats wrong????

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mercedes 220s--sold
mercedes 300d--sold
mercedes300dturbo--sold
mercedes 350sd turbo [will outlast me]
jaguar xk140mc hardtop
mgb [several of them]
mga
mg-td with right hand drive[my 1st car]