What would cause the car to have a rough idle on the first start of the day? It will chug for about maybe 10 seconds or so, then smooth out.

1991 300d 209k

Glow plugs need replacing.

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Moss Gate Bed & Breakfast
1985 300 TD GG done in by a red light runner
1984 300 CD Sold
2008 Titian
2000 Cadillac SLS
1966 FLH Sold
2003 Harley Ultra

Could be one or more of several things. Glow plugs as mentioned above, worn injectors, small amounts of air leaked into the fuel system, worn valves, low compression, or more importantly - perhaps the engine is just cold. Try letting it glow longer (10-15 secs) and see if you have an improvement. If it's really cold, try glowing twice.

The glow lights in the OM60x seem to be REALLY optimistic. My SDL shows the light for maybe 2 seconds in 40˚ weather. It'll start, but it's pretty rough for about 5-10 seconds. Glow it until the idiot buzzer stops, and that first start is smooth as silk. Subsequent starts throughout the day don't require any glow time at all.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

Not sure if I'm having issues or it's just the cold, but my '85 300D will also chug a little first thing in the morning if I didn't have it plugged in over night. I've just attributed it to being a 30 year, 325K mile old diesel in the cold weather. So glow plugs would be worth looking in to?

Glow plugs x2. Your symptom or there about is what I use as my alert to swap in new ones.


Probably the number one glower (front of engine) is heading south. The rest are right behind.


Easy test...Try two immediately consecutive glow cycles of about 45 seconds each. Then hit the start button. If it fires smoother, then you know for sure.


The more miles, the more they like to warm up. At 436k miles and in weather < 50*F I let it warm up at about 1krpm for another 45 seconds. Then let it roll. Happy 603 lol

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1986 300SDL 440,xxx

A long with the other stuff mentioned if the Fuel Supply/Lift Pump valves are worn when the Car sits unused over night the Fuel Could be migrating back to the Fuel Tank.
Newer Lift Pump Repair with Disc Valves
95 E300D (606.910) Fuel Lift Pump Rebuild Question - PeachParts Mercedes ShopForum
606 Fuel/Lift Pump Rebuild
OM606 Fuel Pump Rebuild - PeachParts Mercedes ShopForum

On the other end of that the Fuel Pressure Relief Valve has a plastic piece in it that can warp or falls apart.
See pic.

If there is any fuel wetnes around the base of the Delivery Valve Holders it is likely the O-rings.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

I've heard a few people say it's the glow plugs, but no dash warning light is on. I've had a glow plug light on the dash before when a plug has failed but the car would ultimately start but not chug on start up.

I will try the 2x glow plug to see if that helps.

The light on the dash seems to only have a casual connection to reality most of the time. You can still have a failed GP and no idiot light to let you know about it.

My SDL seems to think it's ready to go after ~2 seconds of glowing when it's 30˚ outside. Not gonna happen. It'll start, but boy does it rock and roll for a few seconds (yes I've tried to see if it would do it!) Glow 10 secs or so and it's silky smooth.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

My mechanic came by today, checked the resistance and said the one glow plug is not putting up enough resistance (if I'm repeating that right).

With previous glow plug problems, my warning light has always come on, but this time it didn't. He said the reason the dash warning light didn't come on yet, is because that glow plug is still providing resistance, just not low enough to turn the dash light on yet.