setting the idel on 300SDL? - PeachParts Mercedes-Benz Forum

2veggiecars · #1 02-17-2008, 07:40 PM

A mechanic told me the idel on my 300SDL was very hard to get to and it would be easier to adjust the throttle linkage. Changing the linkage threw off the power and seem to create other problems, so I don't think that's the answer. Isn't there a simple way to ajust the idel on this car?

bustedbenz · #2 02-17-2008, 09:59 PM

What's the problem with the "idel"? Too fast? Too slow? Unsteady/Fluctuating?

More information would be nice.

There is an electronic idle control knob located near the firewall on the drivers side, it's marked ELR. It could be malfunctioning or simply mis-set.

#3 02-17-2008, 10:08 PM

Your mechanic was wrong on how to set the idle. It is an electronic setting, changing the linkage will do nothing good.

BJ300SDL · #4 02-17-2008, 10:15 PM

If your tech thinks it's too hard to get too, He better find a new line of work!! I just checked and adjusted the low idle on our 300sdl today and it took all of about 3 minutes.

On the rear of the fuel injection pump is a round cover called an actuator. It is about 2 1/2 " in diameter, its plastic and at the top is a two wire plug in. This is how you adjust it according to the factory manual.

Engine at idle, unplug the connector from the acuator. The rpm should drop slightly, (My engine was so far out of adjustment it almost died) check the idle rpm it should be 570 =/-40 with the engine @ operating temp. If it needs an adjustment, the jamb nut and screw are about 1" to the front of the connector you unplugged for the actuator. the jamb nut is about 13mm, and the adjustment screw is a bout a 5 or 6mm, real small. Back the screw out to increase the idle. once you get done with that tighten the nut and plug the actuator back in and the idle should " briefly increase". If you don't notice an increase the actuator might be burned out.

After the screw is set you can tweak the idle using the trimming plug. A round dial located by the fuse box. It's about the size of a quarter with numbers 1-7. Lift and turn to adjust. But do the other adjustment first. Then try this.

Good Luck

probear · #5 02-17-2008, 10:16 PM

Quote:

Originally Posted by 2veggiecars

A mechanic told me the idel on my 300SDL was very hard to get to and it would be easier to adjust the throttle linkage. Changing the linkage threw off the power and seem to create other problems, so I don't think that's the answer. Isn't there a simple way to ajust the idel on this car?

FI is right...describe the actual problem and we'll go from there. You will want to put your linkage back to the original state.

bustedbenz · #6 02-17-2008, 10:17 PM

No offense, but I'd go in the opposite order.

The FSM states clearly that "4" is the desired setting on the electric adjustment knob for the idle. If we adjust it "close" to right with an unknown ELR setting by changing the adjustment screw thing, and then tweaking it with the ELR, both are off-spec.

If we set the ELR to the proper FSM setting first, then adjust the other way to get it right by the tachometer... things are just a little more synchronized.

BJ300SDL · #7 02-17-2008, 10:22 PM

Sorry I was just following how the 602 -603 service manual said to adjust it. Maybe my manual is different than yours.

bustedbenz · #8 02-17-2008, 10:29 PM

Quote:

Originally Posted by BJ300SDL

Sorry I was just following how the 602 -603 service manual said to adjust it. Maybe my manual is different than yours.

If you've got a manual that's more than I had to look at. I was simply giving an opinion based on how I'd do mine... your manual is the same as mine and it's right.

I retract the suggestion.

One reason I was thinking of going in that order was to see if the ELR electronic thing was in fact working, or if it was acting up. If it's acting up, then the problem is found before the more complicated procedure is ever started.

PaulH · #9 02-18-2008, 01:05 AM

Just adjust the ELR knob which is behind the fuse box. As already mentioned #4 is recommended. The values are as follows: #1=570 RPM, #2=590, #3=610, #4=630, #5=650, #6=670, and #7=700 RPM. As I remember, you have to pull up on the knob before turning it. Don't touch anything else; just adjust the knob! Takes seconds to do. Hopefully, the '86 SDL has the same setup. Good luck.

Bill Ladd · #10 02-18-2008, 08:28 AM

Quote:

Originally Posted by PaulH

Just adjust the ELR knob which is behind the fuse box. As already mentioned #4 is recommended. The values are as follows: #1=570 RPM, #2=590, #3=610, #4=630, #5=650, #6=670, and #7=700 RPM. As I remember, you have to pull up on the knob before turning it. Don't touch anything else; just adjust the knob! Takes seconds to do. Hopefully, the '86 SDL has the same setup. Good luck.

Unfortunately, sometimes that dratted actuator for the trimming plug at the pump does not work. Mine doesn't and I haven't traced the problem as of yet.

Following the specific Factory Service Manual directions as BJ300SDL has posted is the way to go. This way, one can set the idle to proper speed with a non-functioning electronic trimming adjuster!

Here's a pic of the idle adjustment screw from the FSM --

andmoon · #11 02-18-2008, 11:58 AM

My 90 350 sdl idles fine but if I rev the motor to ~800rpms, all the diesel shaking is 100% gone. Would it put too much strain on the tranny to set the idle this high?

rosenfe · #12 11-09-2009, 03:27 PM

would these adjustments also help with a surging idle ,my sdl 87 idle goes up and down only at idle,not a lot but enough to be able to hear it surge at a stop light.