Although you didn't specifically say I guess this is for your 83 300D

I think you have two separate problems. The glow plug light flickering could be a dodgy earth.

The intermittent stumbling under acceleration / high speeds => so is it fair to say it occurs in the higher rev range? <= could be something like a weak lift pump.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!