Idle control cable ... my 240D's new puzzle - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 11-26-2009, 09:44 PM

After an epic effort to upgrade my 240D's glow plugs to fast-glow, including the relay, it starts gloriously. Here's the bad news: it idles so slow, it just dies unless I rev the engine a bit, and even then once it goes back down to idle it's pretty violent (not missing at all, just shaking a lot). It probably was caused by my messing around under the cluster to fit the new relay in ... probably jostled the idle control cable. However, the idle cable has not worked since I bought the car. After I fiddled around with it, it now has mild effect, but doesn't last ... i.e., the idle drops back down really low or is just plain erratic. I can physically pull the cable with my hand and the idle smooths out, but it just drops back. By the way, it came with this delightful wire on it:

Is this something I should try to mend by removing and cleaning the cable or should I just buy a new one and replace it? Or do I have another problem?
I was so proud of my glow plug work ... yesterday this car started SO fast, dead cold at 40 degrees ... which would have been a huge struggle with the old plugs. Today, new issue. At least it never lets me get bored!

dealwithit · #2 11-26-2009, 10:07 PM

why not just adjust the idle with the screw on the IP? then you wont ever have to worry about the idle adjust cable?

BodhiBenz1987 · #3 11-26-2009, 10:12 PM

Quote:

Originally Posted by dealwithit

why not just adjust the idle with the screw on the IP? then you wont ever have to worry about the idle adjust cable?

Well, I was thinking there may be situations where I want to turn up the idle just for cold starts, but turn it down once it's warmed up. Although that makes sense to get it to a higher basic idle ... because right now it keeps dropping down to an idle that's too slow for any condition. I'm at work now so I can't toy with it, but I feel like I should address anything that has a rogue wire wrapped around it on principle.

strelnik · #4 11-26-2009, 10:13 PM

Quote:

Originally Posted by dealwithit

why not just adjust the idle with the screw on the IP? then you wont ever have to worry about the idle adjust cable?

First, yes it's worth it to adjust the cable and in your case, replace it. Then adjust the IP accordingly.

I say this because: if you over adjust the idle screw on the IP, you can possibly get the IP to move so far forward when you mash down on the accelerator that the engine will start to run away.

I had this happen to me and I actually slowed down the car by pulling back on the accelerator with my foot.

So be careful not to over adjust.

My 2 cents.

BodhiBenz1987 · #5 11-26-2009, 10:50 PM

Quote:

Originally Posted by strelnik

First, yes it's worth it to adjust the cable and in your case, replace it. Then adjust the IP accordingly.

I say this because: if you over adjust the idle screw on the IP, you can possibly get the IP to move so far forward when you mash down on the accelerator that the engine will start to run away.

I had this happen to me and I actually slowed down the car by pulling back on the accelerator with my foot.

So be careful not to over adjust.

My 2 cents.

Thanks. Good to know. I already had enough of a "run away" scare when I knocked the spring off the throttle linkage earlier this year.

The replacement cable is $50 on Fastlane ... that's not that bad.

holtonmusicman · #6 11-30-2009, 02:10 AM

Where is this adjustment?

JHZR2 · #7 11-30-2009, 09:15 AM

Quote:

Originally Posted by strelnik

First, yes it's worth it to adjust the cable and in your case, replace it. Then adjust the IP accordingly.

I say this because: if you over adjust the idle screw on the IP, you can possibly get the IP to move so far forward when you mash down on the accelerator that the engine will start to run away.

I had this happen to me and I actually slowed down the car by pulling back on the accelerator with my foot.

So be careful not to over adjust.

My 2 cents.

I was thinking of adjusting idle on my 240d a bit, and had done so on my 300CD. Can you ellaborate on this? The IP has stop screws to prevent over extension of the linkages. Not sure what you can do to a diesel to cause it to "run away". Do you really mean to go overspeed/over RPM?

I wasnt really under the impression that adjusting the idle screw moved the IP position, it just adjusted the linkages slightly as to provide a bit more fuel at idle, thus increasing the speed. At the end of the day, that is all that I saw on mine, the idle screw pushed the small black lever under it a bit lower, which just to my knowledge adds fuel. Then, the linkage needs to be adjusted so the stop mechanism can be maintained.

Insight into this would be most appreciated, both wrt runaway diesels and IP movement due to the idle screw.

Thanks!

BodhiBenz1987 · #8 12-05-2009, 03:32 PM

Just a follow-up:
I bought a new cable (and rubber sleeve) from the dealership for $40, and installed it a couple days ago. Very easy job. Ended with an "Ohhhhh so that's how this thing is supposed to work" moment. My old cable was seized, plus the lock ring on the dash was loose, so when you turned the knob, the whole tumbler turned. It was also quite gumbed up at the throttle end of it, and the inner cable had pulled loose from the tumbler on the dash. Now that I've put the new one in and observed how it functions, I can see why the old one wasn't working out. A very cool feature to suddenly have on my car.

So it starts now and stays running, quite smooth. The bad news is, it vibrates like mad, the whole car. I just changed the motor mounts so that's not the issue, although the trans mount may be bad. Just to make matters worse I decided to tighten up the motor mount bolts, and snapped one in half. That's a whole nother thread though.

When I get that fixed I'll play around with the vibration issue ... it's not unlivable.
But, the idle control cable made a HUGE difference. Between that and the fast-glow kit I installed, this is like a whole new car. A new old car, that is.

kwoody · #9 02-21-2013, 10:23 AM

I am sorry to bring this back from the dead... but our cars sound very similar. I am needing to replace, I believe, the idle adjustment cable as well. When I turn the idle adjustment knob on the dash, it just turns and turns indefinitely without ever stopping. On my 220D, it has a set amount it can turn and an impact on the idle, as it should. I also have the shaking problem though, and have just replaced the motor mounts and transmission mount. Did you ever figure it out? The shake is much worse when in drive than in park or neutral. I was thinking it could be related to weak idle...

JHZR2 · #10 02-21-2013, 12:02 PM

Valves and compression are important to know.

Partscarver · #11 02-21-2013, 01:19 PM

What he's trying to say is search the archives. your valve clearance is suspect and related
your compression is possibly low (too tight valve clearances)

kwoody · #12 02-21-2013, 05:31 PM

Cheap fix if that is all it is. It starts up VERY easily in cold weather, even covered in ice/snow. And it'll start in 50 degree weather without glowplugs. I think that means I have very good compression? This engine was imported from mercedes brand new in 1990, and has about 50,000 miles on it.

Stevo · #13 02-21-2013, 05:56 PM

Cold weather starting about sums it up, if it starts, you have a goood engine.

gatorblue92 · #14 02-21-2013, 07:38 PM

Quote:

Originally Posted by kwoody

I am sorry to bring this back from the dead... but our cars sound very similar. I am needing to replace, I believe, the idle adjustment cable as well. When I turn the idle adjustment knob on the dash, it just turns and turns indefinitely without ever stopping. On my 220D, it has a set amount it can turn and an impact on the idle, as it should. I also have the shaking problem though, and have just replaced the motor mounts and transmission mount. Did you ever figure it out? The shake is much worse when in drive than in park or neutral. I was thinking it could be related to weak idle...

When you turn the knob is there any resistance? I suspect the cable may have snapped. Mine did sometime in the early 2000's and I vaguely remember it being a fairly simple fix. One of the first DIY projects I undertook on my 240D back when it still belonged to my Grandmother.

dubadxx · #15 02-21-2013, 11:14 PM

Where is this idle screw on the IP? I see a slotted brass looking screw that won't turn. I'm afraid to strip it. My idle is too fast and I've adjusted all the linkages and removed the cruise control actuator. Still too fast. Any pics?