I posted this on that other forum too, I figured someone here might know something they don't.

I was cruising at 70 on my way home from work, and the car suddenly started decelerating and the tach fell to idle. At first I thought something in the drivetrain had let go, but when I pulled over and looked under the car nothing seemed amiss. I (cautiously) rejoined traffic and she was fine the rest of the way home.

Thinking about it after the fact, I realized that there was no way the engine could idle at 70 MPH in gear (she does ~3000 RPM at 70), so somehow the engine had been disconnected. There was nothing that I could determine as the initiating cause. No unusual noises, no change in road surface/conditions, I didn't touch the CC stalk, shifter, or either pedal. Happened on a straightaway with a mild downgrade.

Things to know:
- my shift bushings are loose as a goose, I have to pull back to the 3 position on the shifter track and then push forward to the stop to pop it into drive
- my girlfriend mentioned the cruise disengaging/not holding once before, but she wasn't able to reproduce it (I was in the car and didn't notice)
- I've shifted into neutral to coast down a hill without remembering to disengage the cruise, and she immediately revved to 5000 RPM. I don't know if that's normal behavior, or if the cruise is supposed to disengage when the trans is in neutral.

How are these systems supposed to interact?

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

It's unclear from your post, are you saying you had cruise control set and it disengaged on its own or you were driving with your foot on the accelerator and it just dropped to idle?

I can tell you from my experience with a later model that if your tires are different sizes cruise WILL disengage. That's because the cruise and traction control/ABS speak to each other and when tires are of different sizes they turn at different speeds and the car thinks a wheel is spinning and it tells the cruise to disengage. Check your tires to make sure they are all the same size and all properly inflated if your problem is with the cruise control.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Cruise control was set, my foot was off the accelerator. The car started slowing down like it was coasting, and at the same time the tach dropped to idle.

I have different brand, same size tires on the front and rear, I suppose they might wear unevenly. However, that still does no explain the engine dozing off.
It's not physically possible for the engine to turn at 650 RPM if it's connected to drive wheels going 70 MPH.

The only way to produce these symptoms (without catastrophic drivetrain reconfiguration) is for the transmission to be in neutral and the engine be receiving no throttle input—in this case, due to the cruise disengaging.

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

I would hope for a slip to neutral.
Change those shifter bushings and see if it happens again.
Euro model or Euro delivery of a Fed '95?

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

My Recommendations:
Shift linkage bushings are cheap. Not very difficult to do. Makes a world of difference.

Lube your linkages. When was the last time that was done?

Check the status of your wiring harness going to the EDS.

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92 300D 2.5L OM602 OBK #59

I have the same thing on my 1995 Mercedes E300D I was cruising at 70 w/cc ON. and on a staraight freeway noticed that i was slowing down with cruise control off and engine ideling, i called up the dealership they told me it could be two of the things the cc amplifier or the linkage..
i haven't done anything after but wil have to.

Not sure. She has US auto ACC and Fed emissions ****, but has some weird things like ortho seats and the bigger fuel tank. Heated everything. Also on her build sheet: "warning triangle delete". Why, God? Why?

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)