I recently bought a 1985 500 SEC. the car turns on fine when cold but once it warms up the engine revs up to over 1500 rpms where it stays at. i have tried to adjust the idle screw but when i move it down even just a couple hundred rpms, it doesn't want to start after that. if i do get it to start the engine runs poorly. all vacuum hoses have been checked and replaced. new cap and rotor, spark plugs, and air filter. economy gauge has always been in the red all the way to the end. is there anything else i can do? thanks in advance for any help.

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Frank

[This message has been edited by Frankster_1 (edited 11-19-2000).]

I have seen manual adjustments on early "Grey market" 500 motors but never an 85. But, if you have an adjustment you must have the old manual system with thermostatically controlled additional air valve.

Engine speed is determined by the amount of air going in. Fuel control and ignition can reduce speed by reducing performance only. If your car runs at 1500 rpm warm it should run faster cold because the additional air valve would be open. It seems your valve may be open all the time. This makes me think your mixture is so rich cold that performance drops and the speed isn't high.

By reducing the idle air, hot, you are are in effect futher enrichening the cold mixture. This is all I gather from your info.

Your starting point should be the high warm idle, where is the air coming from to run that fast? Verify your mixture, the methods of which will vary depending on whether your car was modified for US emissions.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

I have seen manual adjustments on early "Grey market" 500 motors but never an 85. But, if you have an adjustment you must have the old manual system with thermostatically controlled additional air valve.

Engine speed is determined by the amount of air going in. Fuel control and ignition can reduce speed by reducing performance only. If your car runs at 1500 rpm warm it should run faster cold because the additional air valve would be open. It seems your valve may be open all the time. This makes me think your mixture is so rich cold that performance drops and the speed isn't high.

By reducing the idle air, hot, you are are in effect futher enrichening the cold mixture. This is all I gather from your info.

Your starting point should be the high warm idle, where is the air coming from to run that fast? Verify your mixture, the methods of which will vary depending on whether your car was modified for US emissions.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

I wonder if you have an electronic idle system that is failing and you are adjusting fuel mixture? This is what I think. I would bet you have a bad controller or valve and the reason the car will not crank after you adjust it is because you are leaning out the fuel mixture so much.

Be sure you know your adjustments.

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