Surging and Unsettled Idel after MPS Rebuild, '74 2.0L D-Jet Options

[914four]

Running down a bucking issue and found my MPS to be leaking. After rebuilding the MPS and verifying a good seal, everything went back together okay. When I started the car, the engine surged up and down and would not idle.

The electrical connector socket on the MPS does not appear to be keyed and using the diagram below from Clay's D-Jet troubleshooting guide it seems I may have plugged in the MPS wire incorrectly. I ohmed the wires from the ECU connector to the MPS socket and made sure the wires are in the order shown in the diagram.

The wires look to be looping back from terminal 7 to 15 and 8 to 10 so that the socket could be plugged in either way and work correctly. Could plugging in the MPS wires incorrectly have damaged the ECU? If not, what should I be looking for that would cause the surging and lack of idle?

[ChrisFoley]

Kelvin,
You have the adjustment tools. It may take no more than a small change to the center screw to bring the mixture into the proper range.
The first step is to see if turning the mixture knob clockwise on the ecu improves the idle.
If so, return it to the center position and back off the MPS center screw 1/8 turn at a time until the idle smooths out. You can do this with the engine running as long as you don't push in on the diaphragm with the tools.

[914four]

Kelvin,
You have the adjustment tools. It may take no more than a small change to the center screw to bring the mixture into the proper range.
The first step is to see if turning the mixture knob clockwise on the ecu improves the idle.
If so, return it to the center position and back off the MPS center screw 1/8 turn at a time until the idle smooths out. You can do this with the engine running as long as you don't push in on the diaphragm with the tools.

Chris,

Thank you for the direction on the MPS. I was able to turn the ECU knob four turns clockwise and it stopped there. I started the engine and the idle settled down so I turned the ECU knob back to the original position. I adjusted the MPS center screw 1/8 turn counterclockwise but the surging came back. Ran out of time this evening but I'll try to adjust the center screw another 1/8 turn in the next day or so.

Just wanted to give a quick update because I think you have me headed in the right direction.

Thanks again,

Kelvin

[pbanders]

Thank you for the direction on the MPS. I was able to turn the ECU knob four turns clockwise and it stopped there. I started the engine and the idle settled down so I turned the ECU knob back to the original position. I adjusted the MPS center screw 1/8 turn counterclockwise but the surging came back. Ran out of time this evening but I'll try to adjust the center screw another 1/8 turn in the next day or so.

Good to hear you're making progress with Chris's information. Once you get it somewhere close to where you want it, I recommend that you get the idle CO, part-load CO, and full-load CO tested. Doing adjustments "by ear" can produce good results, but it can also leave you far from optimal. If you've put this much work into it by this point, you deserve to get it right. Good luck.

Good numbers for stock 2.0 CO are:

Idle: 3.0 % (I've got mine at 2.5%, but some work better at 3.0%)
Part-load: 2.5%
Full-load: 4.0%