'85 QV Sudden Rolling Idle and Weak Low End

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!

 

Thank you. That's along the lines of what I was thinking. That's why I was curious about a compensating mixture mis-adjustment. Even though I have done a good deal of work on older cars, the 308 is actually my newest and complex electronics are not my strong suit. I renewed all the hoses in the engine compartment last winter, but I will check them again. I also rebuilt the throttle body which I'm quite sure is working well.

 

I definitely agree. I have triple checked the vacuum lines to the boxes, removed the box connectors (cleaned them, although they looked good) and will hopefully check the result later today. I'm wondering if someone far more expert in electronics than I might suggest how a better Digiplex ground, and possibly a resultant stronger "signal," could adversely affect something else. I will also check ignition timing with a light when I get a chance. Faster idle, poor low end power: my initial guess would be fixed advanced ignition. But it would have to be quite advanced and I am not getting any preignition pushback when starting.