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Registered
1990 Mercedes-Benz 300se
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15 Posts
Discussion Starter #1
Hello! I’m new to the forum, having just bought my 1990 300se, and I ran into a problem when going downhill on the highway while using the cruise control. It seems that the computer will let off the gas, engine braking slows the car down, and then the cruise kicks in and jerks the car back up to speed. Is the car supposed to do this? I found that it will do it on even slight downward inclines as well
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,624 Posts
What is your speed and engine rpms when this is happening?
Sounds like you have a hyper active cruise control but the cruise on the M103 engine can be a bit jerky assuming this is a M103. Particularly at high rpms.
 

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SuperModerator
1986/1990 W126
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13,670 Posts
Welcome. Didn't know it was jerky on the 6 cylinder. It always seems very smooth on the V8.
Check for posts on member JamesDean. He rebuilds the modules etc, the module is the most common thing I think.
 

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Registered
1990 Mercedes-Benz 300se
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15 Posts
Discussion Starter #4
What is your speed and engine rpms when this is happening?
Sounds like you have a hyper active cruise control but the cruise on the M103 engine can be a bit jerky assuming this is a M103. Particularly at high rpms.
I have the M103. It’s really apparent above 60, when the motor is doing at least 3000rpm
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,624 Posts
I have actually sent a Private email and posted on JamesDean site in the past (9 months)
He never replied, not sure if he is too busy or not interested or not active.

I can only relay my experience in the matter since I owned my M103 from new.

It is my belief that the cruise control amps for these engines are not properly tuned for every car.
Seems they are OK for a certain weight and auto transmission which is in very high volume production.

You can imagine how harsh they can be with a manual transmission operating at high rpm's if not tuned properly.
I almost took mine back to the dealer when brand new, but since I hardly ever use cruise control, I never did.

Clearly they are tuned well for a W201/W124 with automatic transmissions.
Already with manual they become jerky at high rpms because the gain in the loop is too strong. It needs to be tuned down.

It is probably a matter of adjusting a trim pot or a resistor value in the amp. But I do not know.

For this post, I wanted to warn about this as a similar situation could be the case for a heavy car like a W126 powered by a M103, even if it is an automatic transmission.

If supercooper can respond to the rpm question we can rule this possibility out and maybe it is a real problem with his system.

For example, with my W201/manual transmission to jerky-ness begins around >2500rpm as the engine has increased power output and torque.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,624 Posts
Our post went by each other. Do me another favor and let me know, at 3000 rpm how much of a whiplash you get if you push the stalk up (accelerate) to set it as opposed to down (decelerate) to set it?

In mine i can get a jerky engagement if I push up to set it. And it has been like that since day-1
 

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Registered
1991 300SE, 2015 ML350
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44 Posts
Sounds like worn linkage. Check all the throttle linkage and of course the cruise linkage arm.
Any slack here will directly affect the smoothness of the cruise.
My '91 300 SE has always been very smooth at all speeds.

DG
 

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Registered
1990 Mercedes-Benz 300se
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15 Posts
Discussion Starter #9
Our post went by each other. Do me another favor and let me know, at 3000 rpm how much of a whiplash you get if you push the stalk up (accelerate) to set it as opposed to down (decelerate) to set it?

In mine i can get a jerky engagement if I push up to set it. And it has been like that since day-1
I never go above 50mph on my commute to school, so not sure when I'd be able to test. Have to go way out of town to get on a major highway where I live.
 

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Registered
1990 Mercedes-Benz 300se
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15 Posts
Discussion Starter #10
Sounds like worn linkage. Check all the throttle linkage and of course the cruise linkage arm.
Any slack here will directly affect the smoothness of the cruise.
My '91 300 SE has always been very smooth at all speeds.

DG
I can take a look later today. I have noticed some vibration in the gas pedal sometimes, could have something to do with it.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,624 Posts
I never go above 50mph on my commute to school, so not sure when I'd be able to test. Have to go way out of town to get on a major highway where I live.
Should be repeatable by selecting a lower gear and 50mph if you are interested.
 

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W201 Moderator
89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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2,624 Posts
In that case look into what Dallaswrench is pointing at.

- Cheers!
 

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Moderator
1991 500SEC sub 50K mi. 1987 560SEC Now 150K mi. 2018
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4,290 Posts
Hello! I’m new to the forum, having just bought my 1990 300se, and I ran into a problem when going downhill on the highway while using the cruise control. It seems that the computer will let off the gas, engine braking slows the car down, and then the cruise kicks in and jerks the car back up to speed. Is the car supposed to do this? I found that it will do it on even slight downward inclines as well
In addition to the assistance others have offered, I'll jump in with my own cruise experience with my 560SEC.

Mine has started exhibiting exactly the same symptoms as yours..... Ie, it will seemingly pulse deceleration [in one-second intervals +/-] then acceleration only when going down even the slightest incline at road speed. It can be very jerky and is not at all fun. I have a replacement cruise amp to go in when the weather gets warmer.

I have narrowed it down to the cruise amp on my car and I believe it is the 33-year-old capacitors that have gone south causing this behavior.

Over the years prior to this the cruise was very smooth and very accurate.

MBL
 

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SuperModerator
1986/1990 W126
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13,670 Posts
is not at all fun
Sorry, that did make me chuckle.

What stood out about my cruise before it died completely, was the maxium throttle full kickdown experience while struggling to get it to disengage. With my Mum in the passenger seat. Also not at all fun 😂
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,119 Posts
Not that his will help the OP, but mine was really exciting. It would detect under the set speed and immediately apply full throttle. Then, it detected seriously over speed and released the throttle completely. Wash, rinse, repeat...

I sent the amplifier to James Dean and now it works flawlessly.
 

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Registered
1991 560sec. 1969 280SL
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1,083 Posts
I sent James dean a pm a few days ago. No reply so far. John what did you pay for a reconditioned amp?
 

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Outstanding Contributor
350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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3,119 Posts
I don't really remember, but if I had to guess, I'd say something like $60. It was 4-5 years ago. Back then he had a pretty comprehensive web site, including prices. This may be it, but I'm not sure: http://www.cruisecontrolrepair.com

(Web site confirmed. There's a "Contact us" email there.)
 
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