I had a similar problem with a 93/940 Regina. I did a bunch of stuff, duck tape style. The idle valve was sticking. By giving it current from 3 to 12 and back, I could see that it would not return to close steadily when the volts went down. To clean the valve visible areas was useless, so I cut it open and cleaned the inside, and a little WD-40. I put it back together with a screw and duck tape. Still running. While I was doing all that, I drove the car with a plastic valve from Lowe's. I put it in place of the idle valve and regulate the opening to maintain a decent idle. Try that to determinate that the idle valve is the guilty one.
Also there is a MAP sensors on Regina system. This little antique gadget regulates the fuel trim by sending a voltage rage to the ecu, depending on the vacuum pull. Go figure. I don't think O2 sensor, Maf, knock will change the idle much. Check very carefully for a intake gasket leak. They are hard to trace and can make your idle a disaster. Keep lookig. It will show up.
Of couse if you car is not regina, is another story. I hope this gives some new ideas. It is what is all about. We don't drive a Ferrari anyway.

I changed out the FPR and it did not fix the problem. I'm going to try the temp sensor and the knock sensor next. I've checked for vacuum leak and I didn't find any.

Most likely you have a vac leak or the intake gaskets is craked or loose. You can do a propane test. It will tell imidiatly if that is the case.

If the O2 sensor output voltage is ranging up and down several times a second as per the specs then is would not be running rich. That ranging voltage indicates that the mixtures in within range and is being fine tuned by the O2 sensor feedback to the ECU.

What sympmtoms do you have that is is rich? Fault codes? Perhaps it was running rich before you repaired the wire.
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David Hunter

Fuel Pressure Regulator.

Coolant temperature sensor(under intake manifold) or FPR. See FAQ's for details.