94 Teg Surging Throttle Problem

A few months ago my teg started idling a bit funny. Its got a chipped ECU (not my choice) and has always idled very low (500-750rpm) once warm.

In the past few months however the revs have started fluctuation or surging... Basically once the engine is warm the revs drop right down to nearly 200-250 (the needle actually drops off so its hard to tell), then the engine bounces back up to around 500rpm... It then does this non-stop if I leave the throttle alone.

Ive found that resting on the throttle tends to solve the problem as I'm forcing the system to run constantly, however when letting off the throttle (or dropping out of gear), she drops right down gets really ragged then bounces back up to ~500.

The drop and surge cycle takes roughly 2 seconds.

Ive taken it to an auto electrician who sat on it for 2 weeks and eventually shrugged his shoulders... Luckily he didn't charge me either so...

I've heard that one factor could be the O2 sensor, however another camp has said ECU and yet another said throttle sensor...

So, what do ya'll think?

Details of the car are:

94 Honda Integra (GS-R model)
B18C (Gen 1) motor - Enlarged throttle body, Gizmo chipped ECU, better breathing with a pod etc.

Car ran very well for 5 years with this set up...

the 1st thing I would try is adjusting your atmospheric pressure screw on top of throttle body. Or attempt to find a bad vacum hose.