Rougher idle and popping from the exhaust. What could it be?

[Prime12]

Since last weekend my car seems to be idling a bit rougher. It's not rough-rough (still idles at 750 rpm), but there is more vibration. Once in a while the engine would even shake the whole car sitting at idle. My car used to be lexus-smooth and definitely did not do this before.

Also, the exhaust is now popping a lot more frequently. It is most noticable when I let off gas to shift. I know 3S exhausts gurgle and pop even in stock form but it definitely wasn't this much.

The car is a 97 vr4 with 70k miles. It is stock. Some things that may be relevant are:

1. Plugs are new NGK coppers with 400 miles on them. They were gapped at .375.
2. New OEM plug wires. Again only 400 miles on them.
3. New left and right OEM engine mounts with maybe 200 miles on them. Front is original but it was still good. No clue as to the condition of the rear mount.
4. Drivability has not been affected. It still revs smooth at part throttle and pulls strong at full throttle.
5. No CEL yet.

Any ideas? I am thinking PTU or coils. I found a slight leak on the vaccum hose that goes from the Y-pipe to the wastegate actuator but even after fixing the leak I still have the same problems. Any help would be appreciated.

[Roybatty]

Check IAC Stealth 316 - ISC Servo Motro

....intake pressure test.

[whaleshark]

My service manual 98/99 says to check in this order

Warm engine order- idle air control motor, injectors, closed throttle position sensor, fuel pressure, intake air temp sensor, engine coolant temp sensor, barometric pressure sensor, evap emission purge solenoid, fuel pressure solenoid, 02 sensor

manual also describes symptoms as "idling instability" - hunting-engine speed doesnt remain constant/ changes at idle or rough idle as movement of tachometer pointer and the vibration transmitted to the steering wheel, shifter, etc..