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81 300TDT WAGON , 82 300DT SEDAN, 84 300TDT WAGON(retired),
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442 Posts
Discussion Starter #1 (Edited)
84 300TD.
The car is abused , I bought as a parts car one month ago, but I want to see if I can fix it.

The engine mount is bad, the sub frame mount is bad.
No glow plug light on when glowing, but the engine is right up after turning key in about 5 seconds. So compression is not an issue.

Cold start the idle is rough and engine will stall, the rpm is about 600 on the cluster, after I replaced two fuel filters, and primer pump, it is still rough after cold start, but will not die. If foot keeps pressing gas pedal, idle is fine.

After warm-up(engine running 5 minute), idle is fine only shift gear is at 'P' or 'N'.

Once shift to 'D' or 'L' or 'S' , if my foot is on the brake and the car is stop(such as waiting for traffical lights) , then the idle is rough again, and it is rougher than the time cold start.
Once shift to 'R', if my foot is on the brake pedal, the biggest roughness is coming, the car is like it will be disassembled by itself.



In summary, if the shift gear is at 'D'/S/L/R' and idling, it is very rough.


Today, I chocked front wheels, and put the rear end on jack stand, I found if there is no load, the idling of 'D' 'S' 'L' 'R
is fine.



Can experts shed some lights?
 

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1984 300D
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5,070 Posts
You idle speed is too low. If it is still there there is a sticker that tells the idle speed on the driverside of the Front Cross member that the Hooked Lock is mounted to.

On mine I believe the minimum Idle speed is 750 rpm.

A lot of people do not realize the Valve need to be adjusted on these Engines or cannot do the adjustment themselves or afford to pay; so they just never have it done.
Not sure on the other Engines but the Turbo Engine has Valve Rotators. What that means is that in uses the Valve clearances get tighter and tighter. So an Engine that has not had the Valves adjusted will have the Vlaves opeining too soon and closing late.

On Transmissions it is sort of basic to start with a Fluid and Filter Change. Unlike American Cars that only have a Brass Filter Screen as a Filter there is a Paper Filter Element inside of the Mercedes Filter.

How does the Transmission shift when the Car I moving?
Make sure the Vacuum Line down to the Transmission Modulator is connected and not cracked.
You might want to look through the below Links.
Repair Links
DIY Links by Parts Category - PeachParts Mercedes ShopForum

PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles
 

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81 300TDT WAGON , 82 300DT SEDAN, 84 300TDT WAGON(retired),
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442 Posts
Discussion Starter #4
The valve clearance is good, I checked.
the weird thing is the SLS is up right away after the engine is on. That is the main reason I bought it although the fluid is black now.
I drove it about 500m, I can feel the transmission shifting ,and it is no problem at all once my foot is on the gas pedal.
No vacuum leaking comparing to my running 300dt sedan,all doors are locked right away after I lock the driver side door(less than 2seconds)

One more thing I forgot mentioning, once I put the rear on air and shift the gear, after I move from 'D' to 'P' or 'N', I heard metal grinding noise.


I turned the idle nut about half turn clockwise already. More turn?

Those throttle linkages on top of the engine are replaced by me from another good car. The bell thing on the firewall is fine, boost cable cleaned.

So once my foot is on brake, how the transmission put the engine back to idling in 300d, what kind of mechanism ?
 

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81 300TDT WAGON , 82 300DT SEDAN, 84 300TDT WAGON(retired),
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442 Posts
Discussion Starter #5
300DMAN, You are right.
I increase the idle speed, and the engine is running perfect, except some nailing noise, will do a diesel purge later.
Now I have to check how much rust is the car having under the skin.
 
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