engine hesitates when you lift foot off accelerator

Can be tricky to find without a test-rig analysing in real-time what's happening to ignition and fuel.

Make sure the engine light is not on. Hesitations can be ignition timing related, specifically, the timing doesnt advance quick enough when you re-apply throttle after a short release of throttle. In an EFI car, this could be the ECU, so a reset may help. Does the car idle properly? If it is a bit rough, the IAC valve may need cleaning.

Loose or leaking intake hoses should be checked. Make sure the fuel-cap and any fuel-tank vapor control plumbing is OK.

Dirty injectors maybe leaaking fuel on power-down causing an over rich. Make sure the O2 sensors are connected. There maybe a second one underneath near the cat-convertor. Make sure the oil-dipstick grommet is in good condition. Also consider taking the car back, as they know what they were messing around with.

Jason

Am I missing something here, isn't that what is supposed to happen?

I think he means it bucks slightly on feathered throttle or on slight re-apply of throttle.

Jason

You just had it serviced, possible they knocked or left a vacume hose loose, or wire. look at the terminal block that is jumped for setting timing maybe they left the jumper in place. If it started just after thay worked on it have them look at it.

I got (may be) the same the same kind of behavior when my engine is cold and idle still running fast. I can accelerate ok, run to steady speed like 70mph then if I lift my foot from accelerator, the engine RPM goes down to say 1000 then kick back in at

Pier