W126 300SD idle speed knob - PeachParts Mercedes-Benz Forum

turbozeke418 · #1 10-01-2012, 04:46 AM

Has anyone added an idle speed knob like in the W123's to turn up the idle? My 83 300SD runs great, but is a little rough for the first minute of running. If I give it a little throttle she smooths right out. I was thinking about hooking one up. Unless someone has a more creative idea? I also would like to kick up the idle a little for when its colder since I run the car on WVO. Thanks!

vstech · #2 10-01-2012, 08:08 AM

are your glow plugs all working? it sounds like you have one or more that isn't getting hot.

supercub · #3 10-01-2012, 09:08 AM

The IP should regulate the idle speed. Mine wasn't working right when I brought it and I was using the knob, it had to be constantly adjusted until warmup. If left on the engine can race when you come to a stop. Not sure how the idle is regulated on the '83 but check it out.

toomany MBZ · #4 10-01-2012, 09:31 AM

Times two on the glow plugs.

JamesDean · #5 10-01-2012, 11:06 AM

There is an idle speed adjustment screw between the IP and the engine if you look down that area. Just be careful not to over tighten the lock nut on it... Don't ask me how I know.

If you want more adjustment than whats available, I'd recommend getting a tap kit and adding some threads onto the screw or just replacing the screw with a piece of all thread. You would lose the ability to use the STOP function in the engine bay though.

toomany MBZ · #6 10-01-2012, 12:08 PM

Idle adjustment, see attachment.

Should be ~750 rpm.

Zacharias · #7 10-01-2012, 12:16 PM

Quote:

Originally Posted by JamesDean

Just be careful not to over tighten the lock nut on it... Don't ask me how I know.

Don't try to snap the locknut loose if it isn't cooperative by either whacking the ratchet or applying lots of pressure, either. Spray it with penetrating oil for a day or two then try again. You only get to find out how unexpectedly fragile the entire assembly is... once.

turbozeke418 · #8 10-02-2012, 02:16 AM

Thanks. I checked all the glow plugs with a test light and and they are all showing on when I turn the key. They stay on till after the cars started too.

spdrun · #9 10-02-2012, 02:33 AM

Did you put the test light across the glow plug, or did you disconnect the glow plug's wire and put the light in series? The latter is the correct method, since it tests whether electricity can flow through the plug -- i.e. it's not open circuit.

turbozeke418 · #10 10-02-2012, 04:27 AM

Quote:

Originally Posted by spdrun

Did you put the test light across the glow plug, or did you disconnect the glow plug's wire and put the light in series? The latter is the correct method, since it tests whether electricity can flow through the plug -- i.e. it's not open circuit.

I touched the test light to end of each glow plug

vstech · #11 10-02-2012, 07:43 AM

all the test light is telling you is if there is power to the plug, not if it's actually working. it would be like testing a light bulb by measuring power at the switch... your tester would say there is power, but your EYES would tell you the light bulb is out.

you need to measure the amps it's drawing, or measure the ohms the plug is resisting to ground. or the best way to know if the plug is working is to pull it out and apply voltage to it, and see if it glows.

toomany MBZ · #12 10-02-2012, 11:45 PM

Agreed, you need to check resistance, use an ohm meter.

turbozeke418 · #13 10-04-2012, 06:22 AM

OK...I've learned a lot over the years and basically afraid to learn an ohm meter. I have one. I have no clue what to set it at or which of the 4 ports to plug the black and red wire.

vstech · #14 10-04-2012, 07:54 AM

Mercedes Diesel Glow Plug Repair

turbozeke418 · #15 10-04-2012, 06:18 PM

Again...as always. AWESOME! Thanks