Keir Gale

Hi,
Looking for a bit of advice...
Spent the last few days putting an OBD1 H22a into a OBD2a EK shell.
It has a bit of a funny issue, that I've not encountered before.
So ignition on, EML is on and gives a code 20, ELD, however the ELD has been disabled on the chip in crome.
That's the only code that it gives with just the ignition on.
Start the car, and it stutters every 5-10 seconds, and then idles sweet again. These stutters seem to always happen within the same time frame. The car revs fine, and idles nicely when it's not doing it's stutter.
By stutter, I mean it bogs out and then misfired into life again. If it stutters whilst reving, it just causes a horrible misfire and refuses to rev.
So sat in the car, at the exact same time as it stutters, the EML will go out, and then come back on and it runs fine again. The main relay clicks every time it stutters aswel.

Initially thought it might be the main relay, but I've tried another one on it and no joy.
Tried the socketed P28 in another EK, and it seems fine in that, so I'm sure it's not the ECU or chip.

To me, it seems as if the ECU isn't getting/pushing out power for a split second, causing the stutter and hence the EML going out. Would also explain the main relay clicks.
The only thing putting me off that idea, is that surely if it was a dodgy wire the time gap between each stutter would always be different, whereas it's identical every time.
Are there set Ground wires for the ECU? Would be no harm in checking them.

Anybody got any ideas on this? I've tried searching over and over again, but to not much avail.