I just bought a beautiful 83 300D and I need some help getting it to run perfectly.

First my Tact and clock do not work? What could that be?

Then when I engage my cruise control the car maintains the speed but the constant speed is jerky. Now when I am holding a constant speed without the cruise on I an feeling the same jerky movement.

Any suggestions would be a great help.

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83 300TD
Wayne Bentley

I feel your pain
start searching for threads about re-soldering the cluster - it sounds related.

could also be a bad ground.. .possibly even a fuse??
I just cleaned out my overboost protection solenoid today. Even though I have had no issues with fuel or acceleration, I found a vast improvement.

on the firewall side of your intake manifold is a banjo bolt with a clear plastic hose running from it. Remove the bolt and clean it thoroughly.

another cause may be failing fuel lines that allow air into the fuel upon demand. Or clogged fuel filters.

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Vacuum does not control the cruise control on your car. Its all electronic. I have a similar problem with my cruise control and I think my problem may be the speedometer cable. Does your speedometer "bounce"? (most noticeable at lower speeds).

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'83 300D 198,000mi Howard
'03 Saturn Vue CVT 75,000mi(wifeys)

yes my speedometer bounces at low speed, unlike everyone else on this forum I am not mech. inclined so I have to take notes and go find a good mech. Thanks for any help you can give. i will change my topic line to something more specific

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83 300TD
Wayne Bentley

The tach is more than likely the amp, under hood, drivers side inner fender, a black plastic garbage can can looking thing. It unscrews. Do a search for tach amp. Yet, I just replaced mine.
Clock, not sure, but one of mine doesn't work either.
Cruise control is usually the amp failing. Under the dash near the steering wheel, you'll notice an aluminium box, that's it, they fail routinely.

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83 SD

84 CD