308 '85 US QV Sudden hunting idle and poor low-end power

Discussion in 'Technical Q&A' started by daynyc, Jul 20, 2020.

  1. daynyc

    daynyc Rookie
    Silver Subscribed

    Aug 5, 2016
    My ‘85 US QV seemed to be running fine. The only thing I did was, very gently, open the Digiplex compartment to peek at the boxes (which looked fine). Thereafter, at a stop the idle would drop down to around 600 RPM before going back to 1000 RPM and the car had reduced low end power. So I went back and connected some good new grounds to the Digi boxes. As a result, my idle was immediately much faster, but rolling, and, although the car runs, low end power is even worse. It seems to run normally over around 3000 rpm. There is no backfiring, obvious missing, smell of fuel, exhaust smoke etc.

    When I alternately pull the coil wires, each four-cylinder bank starts, idles and revs the same. I have done my research and realize, in theory, there could be scores of reasons for this problem. Coincidences do occur, but before I tear a bunch of things apart in phase two of my restoration this fall (new fuel pump, accumulator and filter, replace sensors, plug extenders, check distributors, check WUR), I'm trying to come up with something that may relate to the Digi box examination or the new grounds.

    If both banks individually run and rev similarly and fairly smoothly, I'm guessing the crank sensors or distributors are not the culprits. The original mixture screw plug in the fuel distributor at least looks undisturbed. Hoses, including the vacuum lines to the Digiplex boxes, seem fine. My next easy things to check are the cold start injector and auxiliary air valve, then a timing light. Any thoughts would be greatly appreciated!

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