1988 560 SEL Odd Acceleration Behavior

Within the past month, my 560 SEL began to behave oddly. When the car starts cold and is run between 25 and 55 mph, it seems to be fine--plenty of power & smooth acceleration. Running at a constant 55
mph on a level stretch of road for about two minutes (so there is no change in the pressure I am applying to the accelerator), it suddenly accelerates, as though a load has been removed from the engine. It seems to do this consistently as the engine warms to about 60 deg. C. After this initial surge, the car behaves as if nothing has happened. I'm wondering if this is a sign that my water pump is about to fail or something worse.
The car has one other problem I know of, but I don't see how this could contribute to the strange behavior. The rear suspension has become very stiff over the past six months. The hydraulic fluid is also very low in the reservoir, but there is no sign of fluid leakage that I can see, so I am thinking that the gas has leaked out of the accumulators. If that leads to the fluid pump operating a lot more than it should, could that be the extra load?
I guess I should also mention that the car has a bit over 197K miles and the timing chain was changed this past August.
Cheers! -Tom
Williamsburg, VA 1988 560 SEL 1989 260 E And once the proud owner of a secondhand 1979 300 D 1980 240 D 1982 300 D turbo 1985 380 SE
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You are on the right track as far as the load is concerned due to your rear suspension. It is probably related.
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My 420 SEL does the same acceleration thing once at around 60C. I was under the impression that it was the computer changing the mixture (or something) as the engine warmed. It's undetectable if you're not on a level road with constant pressure on the accelerator pedal.
John
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Well, I've had the car a couple years now, and have been making the same trip most mornings for that time, and I noticed it for the first time only within the past month. It's possible that I've simply not noticed before, but I doubt it. I thought that it had something to do with the engine temperature, as the thermostat should be opening around the same time; however, I've not had any feedback (in this group or elsewhere) that supports that.
I put it in the shop today for work on the rear suspension (min cost of $500 if it's only the accumulators, and I'm not willing to put much more into it than that!). I'll post a follow-up as to whether that fixes it or not.
Cheers! -Tom

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Thanks, Tiger and John.
I had the rear suspension worked on, and the car certainly rides better; however, the acceleration oddity still happens. I only really notice it when it is relatively cold outside, and I've decided that it's such a minor thing that I'm going to ignore it until something worse happens! Thanks again.
Cheers! -Tom

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