Relay / Rev blip / cut out

[SMerK]

Have an issue.  1400 Supersport on standard Rover ECU.  When running the relay situated underneath the ECU clicks and the revs fall from 1000 to 800 then up to 1600.  Occurs frequently with normal revs inbetween.  After a few clicks the rev change cause cut out.

Have done the following step by step.  Each time the issue reoccurred. so tried the next step.

- Swapped relay for new one

- Replaced original relay

- Swapped ECU for my spare (same Rover type for 1400 SS).

- New Battery Neutral Earth Lead.  Old ones ends not looking good.

- Lambda sensor loose in exhaust.  Tightened up.

- Lambda sensor connector not seated in full.  push together.

- All spark plus removed & checked.

Checked all other sensors / connectors looked OK (even if not sure what all do!)

Still going it! .   Any Ideas welcomed.  Thanks.