2001 civic shakes/hesitates at low speed, idling
 

Have a 2001 civic with 73,000 miles, as of late at low speeds and at
times while idling at lights,
the RPM gauge will go down close to 0, the car will shake (quite a
bit), feel like it is going to stall,
but not stall. If you step on the gas it doesn't accelerate much at
all, then after 10-15 seconds it suddenly goes back to normal and
accelerates. (this never happens on the highway, only while
idling or at low speeds)

Have had the following done thus far:
- changed spark plugs
- fuel system flushed
- fuel injectors cleaned
- timing belt and water pump changed

No one (local garage and the dealer), seems to have a clue as to what
the cause it,
appreciate any suggestions....