Get some carb cleaner or engine starting fluid...spray it, while idling, around the base of the intake manifold, the back plate, and at the throttle body joint. Additionally, spray around the hoses that come from the TB - to the brake booster and the charcoal canister. Spray all over and listen.
(If you need to know what to hear for, spray some near the intake filter assembly, right headlight. You'll hear the difference)
If idle changes, you've an air leak of some kind. Isolate it further by using the spray.
If you can't find a leak, check fuel pressure to start.
Hesitation and misfire = fuel/air problems...
Report back and I'll help you figure it out (I've a 540iA, myself)