I have a 2002 Subaru with 105K miles, automatic.  I have replaced plugs, ngk, and swapped in oem wires and coil.  The car will occasionally hesitate from idle after warmed up.  Normally a slight pressure on the peddle will rev the engine from idle to 1000+ rpm instantaneously.  One in 10 times it hesitates for 1-2 sec.

 

If the car had the MAF, I would suspect that.  But it has the pressure sensor instead.  Could the throttle position sensor be a problem?  I have had a failure with a 90's TPS, but it set a code, and it wasn't during acceleration anyway. But I assume that the signal from the TPS starts the increased gas injection from idle so I suspect it. No helpful codes of course, except once, a misfire code on 3 cylinders.

yeah - I think you can use an ohmmeter to test for smooth TPS transition - but the problem seems little more like a sticking throttle plate??? not sure

 

 

you may be overdue for a timing belt system service unless it was done in about 2011 or so.

Throttle plate sticking?

 

Throttle plate sticking

Yes, I suppose that would account for it.  I really cleaned it very well a year ago, but that doesn't mean it's not sticking.  I replaced the timing belt and all pulleys 30K miles ago.