1979 Mark V Engine Surge

Hi Bill,
I have a 1979 Mark V, when the engine warms up – it surges up and down when in park or idiling. It runs ok when in drive with my foot on the brake, or when i am driving normally.
Whats up?
Chuck
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Hey Chuck,
Problems such as this one usually require a hands on type of diagnosis but I will try to give you some basic items and ideas for checking it out.
I am assuming also that your spark plugs, high tension wiring, timing and other tune up items are in good order. First and foremost, try to remember if the surging started immediately after a component repair or any type of overhaul such as carburetor cleaning, distributor servicing, etc. etc. If so, it is important for you to stop at this point and back track to that component and re-check to determine if it was indeed serviced and set up properly. If that is in order I would then move to inspect the “dreaded” vacuum lines and sensors for the engine management located under the hood. This includes the distributor Vacuum Advance and the Choke Pull off and of course the choke operation itself. Another possibility to consider is if the engine thermostat is stuck in the open position and not allowing the engine to reach its full operating temperature. Some of the sensors for the smooth operation of the engine are calibrated to operate and respond with the engine at its actual designed full operating temperature.
Accurate diagnosis with this type of problem is more than half the battle and we hope that the above suggestions will help lead you to a quick and successfull repair.
Sincerely,
Bill