That cam is on the ragged edge of what the stock tune can deal with. If everything else is set up perfectly then it *should* be OK, but any small thing out of spec can cause issues with the idle and running at low RPM - especially even the slightest vacuum leak. Obviously cap / rotor / plugs / wires all need to be in good shape, but I'm sure you've looked at all that. For vacuum leaks you should first check the L-shaped rubber fitting on the MAP sensor and make sure it's not cracked and it's connected properly. Then there's everything on the intake manifold... the throttle body base, vacuum hoses / vacuum caps, injector o-rings, IAT sensor, and EGR valve. If all that checks out then the intake gaskets could be leaking. And I suppose the map sensor itself could be bad but the service manual doesn't really give you any way to test it without a DRB, it just tells you how to check for correct voltage and grounds - so it probably requires a parts cannon test (i.e. replace it just to see if it's bad). Since you did all that wiring so I'm assuming you have a 1994 service manual?
On the topic of fuel economy calculations, you don't need a working speedo or fuel gauge - just a smart phone. Fill your tank, and use a GPS app to tell you how far you travel every time you drive the car. The next time you fill your car record the amount of fuel you put in and you'll be able to calculate the MPG. You'll have some variation between tanks because you can't be sure you're filling it up to the exact same level every time, but it will all even out over the course of a few tanks of gas.