hi all,

my 83 300SD still has the hot idle shakes. starts up right away even in 20F. idles smooth when cold. acceleration is awesome (one of the faster SD's what i have owned) here's what i've done (all of this needed to be done anyway, but i'm still bummed about the hot idle shakes)
-new motor mounts/ transmission mounts (all Lemfoerder OEM with the star ground off)
-new injectors (pop tested, etc.)
-new fuel lines (there are no visible air leaks in the clear lines from the secondary filter to the IP)
- cleaned tank, new fuel tank strainer
-new engine shocks
-new gold colored rack damper pin (played around with that for while and there's a definite slight change in engine sound when it hits the sweet spot)
- valve adjustment (about 5 of them in a month period; kept going tight but i think it was from the vehicle sitting for long, did italian tuneups inbetween


-chain stretch is about 2 degrees (checked via 2mm lift method), engine and IP has about 80,000 miles on it (rebuilt by reputable company{can't think of the name right now])
-messed around with idle speed but it shakes unless i go over 850 rpm (can't leave it that high since it will accelerate on its own going downhill)

Here's what i'm thinking (only ideas, would like feedback on these):

1. i'm guessing that the timing itself might be off; if i loosen the 3 bolts that hold the IP in and start rotating it will that affect the roughness of the idle?

2. the IP might be gummed up, would filling it with acetone (or something else?) help?

3. something went wrong during the rebuild (not likely, but i'll throw it out there)

ANY IDEAS WILL BE GREATLY APPRECIATED

__________________
1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL

define new injectors?

have you tested warm compression?
if you have a low compression pot, you will have a rough idle...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

new bosio injectors, pop tested and balanced (the rough idle was there before the injector swap). i did a compression check early on (last year), can't remember the exact specs but i do remember them being very good across all cylinders (low 400's)

__________________
1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL

then I'd tackle timing next.

it's possible you have a cam offset key in yours already, which would push the IP 2° plus whatever the offset is...

it could also be IP wear/delivery valve adjustment out on a cylinder, or lift pump weak spring resulting in low fuel pressure to the pump... contact funola for a fuel pressure gauge kit.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Valve adjustment okay? Ever consider what the milli volts of the glow plugs are hot versus cold?

You want to make sure the relief valve is overflowing or perhaps with a hot injection pump somewhat worn might be thinning the fuel a little too much for one element to deal with . Check for air in the fuel after warmup? Get some clear line in there to check.

[QUOTE=shadetree77;3135421..........
-new fuel lines (there are no visible air leaks in the clear lines from the secondary filter to the IP)
- ...........[/QUOTE]

this will only show air entry before the secondary filter. to see air entry after the secondary filter such as IP, injectors, injector return lines, you need a clear cigar hose.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

i thought everything after the lift pump is pressurized, would't there be a fuel leak?

__________________
1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL

Good point But due to the pulsing nature of the pump and check valves not being perfect, it is possible for parts of the circuit to be under vacuum at some point of the stroke. The idea is that no matter where the air is getting in, it all goes back to the tank and the cigar hose is a good place to look.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

thanks for that info, didn't think about it that way

__________________
1983 300SD (daily driver)
1991 420SEL (work in progress)
1979 300SD (future replacement for 83 SD)

RIP:
1983 300SD (totalled)
1986 420SEL

Might be time to check the Fuel Supply Pressure.

Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment - PeachParts Mercedes ShopForum

Idle Shake gone after Fuel Supply/Lift Pump cleaned
Fuel Pump Suction/Delivery Valve - PeachParts Mercedes ShopForum

If the above Fuel Supply Pressure is OK I was reading on one of the other Forums that there is another Idle Adjustment Screw but this one is inside of the Governor of the Fuel Injection Pump.

Idle screw inside of the Fuel Injection pump effects on A/C Post #6
http://www.peachparts.com/shopforum/diesel-discussion/319144-wm-injection-pump-idle.html

Injection Pump fuel adjustment for Mercedes Diesels, Bosch M and RW governors - Competition Diesel.Com - Bringing The BEST Together

I have not re-read the above so am not entirely sure they apply.

Also the wording is different than I am used to. When I was in Trade School I was told that Fuel Injection Pump Governors have something called a Governor Droop Adjustment. What that has to do with is how fast and well the Governor deals with the load put on it.

If the adjustment is not correct the Governor may keep hunting to try to get an even idle. This adjustment can change due to old Governor Springs or wear in the Governor and other factors that would cause a sticky Rack.

However, I don't know enough about these particular IPs to know if that is what is being spoken of in the Threads.

__________________
84 300D, 82 Volvo 244Gl Diesel

Rack damper bolt?

__________________
83 SD

84 CD

You tried adjusting the rack damper bolt, but did you try moving the idle up or down and then moving the bolt?

Not all of these cars 'want' to idle at the same spot as they age, regardless of factory spec. For example, one of my SDs would only idle smoothly at what I thought was a painfully low setting. Also on some cars the 'sweet spot' is an insanely fine specific point in the rack damper bolt adjustment.

Try moving the idle up and down (depending on where you are now, there may not be room to go down) and adjusting the new rack damper bolt then.

__________________


Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22