500SEC mystery problem?

Heres the symptoms:
Feels like the handbrake is on, or it's towing a 5 ton caravan , really slow to take off. Feels like the brakes are on, but as soon as I knock it into neutral, it
coasts easy. Economy meter stays half way up, as if accelerater was half way down, even when idling,backing off & cruising. Not running hot. If I give it full throttle, it goes average, whereas before it would take off like a rocket. Suspect something in the trans, but is supposed to be a recon (I only recently bought this car, and has been running great) any clues? thanks in advance
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IMHO more data is needed to determine if the problem is engine or transmission related.
This is a 4 speed automatic; if you start off (from a dead stop) in L the transmission will be (and stay) in 1st gear. Shift up to S and then immediately back to L, that will be 2nd gear. Shift up to S for 3rd and D for 4th. Does it have all 4 speeds?
Idle the engine and open the hood. Listen for a hissing sound - vacuum leak that would account for the odd economy reading.
Does the engine run smoothly? Or shake?
Has anyone worked on the engine? Could the ignition timing be badly retarded - it would start easily but have poor acceleration and power.
What about the fuel? Good or off brand?
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I had the same problems and changed everything to do with spark and fuel that I could. Don't mess with the timing or anything else unless you fully understand this engine. I replaced the spark plugs, fuel filter, wires, dist cap or coil pack I don't remember which it was, rotor button twice, Idle control valve, fuel pump relay, ran fuel injector cleaner from MB through it several times, changed the oil to a lesser viscosity, changed transmission fluid and filter and nothing really worked. If you are comfortable try taking the plug off the Idle control valve. Then hook a test light to your negative side of your battery then touch the inside of the plug you just took off the wires for my 84 500sec were black and yellow. Touch one at a time, if you have the same problem I had it should short out the Idle control system and it will raise and steady the idle. The unit I think is called Lambada idle control or something like that. It is the black box under your hood right up on the firewall under the windshield closer to drivers side. It's connected to a wiring harness and is about 5"tallx6"widex1"deep and has chrome connectors when unplugged. This thing is responsible for all the fuel regulations, when the Idle control valve opens and closes etc. So it is very important and can make you think your fuel pump and everything else had gone bad. I finally had my car checked by a place called AutoHaus here in Indiana after spending a fortune trying to diagnosis it myself. They charged me $150 to diagnosis it and applied that to the labor since I had them fix it. They found me a used unit somewhere for about $300. My total bill was around $500. Now my car runs great again. I hope this helps. If you need the name of that unit for sure I can look it up and let you know
-- Serena
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