[Flieger]

First, always remember the proper sequence to tune MFI from the Bosh "Check, Measure, Adjust" manual.

The way to fix this is to send the throttle bodies, crossover linkage, and everything to a place like Eurometrix but you say you don't want to. They will refresh bushings, bearings, and ball-cups. The throttle return spring is on the MFI pump and you should get a replacement.

The throttle bodies themselves are magnesium and the butterflies will wear grooves in the metal as the intake reversion pulses hit them from the S cam timing at low RPMs. This will allow air to bypass at low revs and cause noise and less power. The way to combat this is to set up the butterfly stop screws so that the butterflies are just barely open when on the stops so that they do not contact the inside of the magnesium bore. If yours are old and have a groove worn, they will need a pro to help them.

If your concern is to get the microswitch to close, just use the adjustment screw on the arm on the crossover tube/rod. Much like adjusting a valve, tighten the adjustment screw to get more throw on the arm and get more force from the throttle spring.

The microswitch only operates above 1500rpm, though. The RPM transducer/speed switch sends the signal that the engine is above 1500rpm, allowing the microswitch into the loop. When the microswitch closes at that speed, it cuts off all fuel until the RPM drops to 1300, where the speed switch deactivates the microswitch and signals idle fuel flow to keep the engine from dying.

Maybe your MFI injection pump is set too rich on the idle end for your climate and driving style?

Remember to CMA before adjusting the pump, though.