Thanks for the additional info, Michael.
My instinct here is the throttle position sensor (TPS), which can be checked fairly easily with a multi-meter. Have your mechanic take a look at this for you. Otherwise, it’s not very complicated. If you have, and know how to use, a multi-meter, it’s a test you may can do yourself. Lots of videos out there demonstrating the actual step by step on how to test a TPS, without removing any parts. A replacement TPS is not terribly expensive and it’s also a fairly easy procedure, if this turns out to be the problem.
While you’re working right there with/around the throttle body, and especially if the sensor checks ok, you may want to remove the air intake to expose the throttle plate, and inspect it for carbon build up on the edges which could interfere with the throttle plate action. Also make sure nothing associated with moving the throttle is mechanically binding, etc., as in this action the movement needs to be fairly smooth.
Otherwise, briefly, after eliminating the TPS as the culprit, here’s the order I might go at:
check fuel pressure - if not ok, check fuel pump; if ok, assume pump/pressure ok.
check for spark - if not getting spark (at the cylinders), check rotor button, distributor cap & wires; if getting spark at cylinders, check ignition coils and spark plugs.
Hope this helps. Good Luck.