Engine running/power issues HELP, Need help diagnosing vacuum/electrical issue? Options

[beng295]

Hi all,

I have scoured the forums and any/all articles I could find out there without much luck. Any help of a point in the right direction would help greatly...

Anyway, I recently got ahold of an all original '72 1.7L (D-Jet, oil bath air filter, and all, with 61k original miles), and am attempting to diagnose a poor idle and LOW power.

Starting up cold idle is around 1.5-2k rpm for around 20seconds and slowly decreases down to a repetitive fluctuation between 400-1000 rpm (sporadic puffing from the tail pipe like a cylinder or two is misfiring). I can pull the electrical plug from cylinder 4 injector and no change to the way the engine runs so I am assuming this is at least one of the misfiring cylinders. Ignoring the idle issue, getting it out and driving it... is difficult as it has almost no power (no acceleration and I can barely get it backed up my driveway to pull it back into the garage) like it's only running on 2 cylinders.

I do want to note that I noticed the adjustment on the computer (assuming this is the fuel adjustment at idle - lean/rich adjustment) is turned all the way up and it will not idle at all if I turn this down to the factory marked position (it was like this when i purchased the car).

All vacuum lines are 2 days new, not leaking and routed correctly, vacuum advance/retard working properly (as far as I can tell), new cap/rotor, wires, plugs (properly gapped), valve lash adjusted on all cylinders...

Now here is where I'm personally confused and lost... If I pull the vacuum line from the MPS, almost EVERY issue is corrected (Idle is almost perfect, and power/acceleration is restored when driving around). I did take a quick look inside of the MPS and there appears to be no damage, and also as far as I can tell (without a vacuum tester) it does hold vacuum. I can plug the vacuum line back in and the idle increases by about 500rpm for a couple seconds and then immediately goes right back to running like garbage.

Am I thinking too deep into this issue or do all signs point to a faulty MPS? Thanks for any help you all can give.