Sudden full throttle - Page 2 - Mercedes-Benz Forum
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post #11 of 66 (permalink) Old 02-17-2019, 07:38 AM Thread Starter
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Note to self:

At GTGs let Jyuma park first and turn off his car....THEN proceed to park beside him.
I'm still not sure it was me... it could have been the devil working his sinister plan.

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post #12 of 66 (permalink) Old 02-17-2019, 08:02 AM Thread Starter
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Holy crap... it just did it again and I wasn't even in the car.

I was working on changing one of the bulbs in the instrument cluster and had the car idling in front of my garage. I went into the basement to get my voltmeter when I heard the engine suddenly go to full throttle. I ran back outside and found the engine screaming at full throttle. I immediately turned the key off and thanked the gods that the engine didn't rip itself apart.

The linkage is fine, so I'm thinking Cruz-control. That's the only thing that could advance the throttle all by itself.

I need suggestions.... I disconnected the rod to the Cruz-control but I don't know what else to do.

@nobby You can feel comfortable parking in front of me. I didn't do it.

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post #13 of 66 (permalink) Old 02-17-2019, 08:28 AM
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Put spike strips in the back of your garage. I still don't understand these idiots who think a stuck throttle is unstoppable. All cars have a neutral gear and brakes designed to overpower the engine.


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post #14 of 66 (permalink) Old 02-17-2019, 08:40 AM
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I had this happen to me once. Turned out to be spark plug wires binding with the linkage and air cleaner.

Do you have factory OEM spark plug wires with the casing around them? Do you have the wire assembly routed through the holders at the side of the cam-covers? Here's a picture showing what it should look like:


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post #15 of 66 (permalink) Old 02-17-2019, 08:40 AM Thread Starter
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How can full throttle possibly be an acceptable failure mode?

I was not even in the car... it was freaking idling one second and full throttle the next.

If my suspicion is confirmed about the Cruz-control being the cause then every Mercedes out there using the same Cruz-control could be a ticking bomb.

Photo of linkage. Red arrows show clean and lubed pivot points.

Sudden full throttle-mercfullthrottle1-copy.jpg

Second photo red arrow shows clean and lubed pivot point at the air intake.

Sudden full throttle-mercfullthrottle2-copy.jpg

Third photo red arrow shows where the rod coming from the throttle linkage was connected to the Cruz-control (rod now removed).
The Cruz-control is the only thing that could possible cause the throttle to go to full with no one in the car (I think).
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post #16 of 66 (permalink) Old 02-17-2019, 08:45 AM Thread Starter
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Originally Posted by Steve Guilford View Post
I had this happen to me once. Turned out to be spark plug wires binding with the linkage and air cleaner.

Do you have factory OEM spark plug wires with the casing around them? Do you have the wire assembly routed through the holders at the side of the cam-covers? Here's a picture showing what it should look like:

Wow! What a gorgeous engine.

Yes, everything is routed properly. Anyway, the throttle just went to full with me not even in the car, so it isn't anything binding that won't allow the throttle to return to idle. The throttle went from idle o full on it's own.
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post #17 of 66 (permalink) Old 02-17-2019, 08:51 AM
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Well...your next post answered my questions.

OK...let's take this through on a functional level.

As we know, an engine is nothing more than an elaborate air pump/heater that happens to turn a wheel. Given the fact that the engine does the suck, squish, spark and spew cycle, there's nothing other than spring pressure on the throttle linkage to keep the engine from running away. If you disconnect the springs and start the engine, the suction generated by the engine would cause it to over-rev.

I'd definitely start with disconnecting the cruise control - just to eliminate that from the equation - and then focus on throttle linkage back pressure.

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post #18 of 66 (permalink) Old 02-17-2019, 09:28 AM
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Beautifully detailed engine, Steve!
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post #19 of 66 (permalink) Old 02-17-2019, 09:49 AM
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A couple of questions/possibilities. Or maybe not. I don't know. Since cruise control is apparently canceled by the unit's reading increased resistance produced by illuminating the brake lights, and since jyuma's brake light switch is not working, could it also be possible that the cruise control unit is receiving an accelerate "signal" due to a short, or other electrical impedance being generated due to the brake light switch being "faulty"?

Or, I don't know how similar, or dissimilar the electrical systems on 560s, and 380s are, but I learned very quickly that on my 560, there is a separate wire connected to the battery's positive terminal via the connector tightening bolt, which runs directly to the idle speed computer, and if it is not tightened well enough (to conduct), the 560 will "idle" at 2,600 RPM. This happened after I only placed the cable on the terminal without tightening it as I was just going to move it around in the driveway.
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post #20 of 66 (permalink) Old 02-17-2019, 10:04 AM Thread Starter
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I disconnected the rod going to the cruise-control. If it happens again then we'll know it wasn't the cruise control. If it doesn't happen again then we'll never know.

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