When warmed up (ie after about 10 miles), my N-reg 214Sei refuses to rev over about 4000rpm (sometimes less!).
I took it to Rover who said it sounded like a HT fault, but "could be the ECU". I booked it in for a diagnostic check, after which the garage said it "could be the ECU" !
New rotor arm didn't help! Any ideas ??>=(

It could well be a melted (blocked) catalyst, T.

Whenever a car comes into us with your problem, we always check the cat first. Usually disconnecting the cat and running the engine (ear protection required!!) confirms the fault.

Otherwise a T4 diagnostic will (or should) show up something :eyes

Oh yeah-The cat HAD failed and was duly replaced along with the backbox, but the fault remains. What IS a T4 diagnostic and would it show a failing ECU?
Rover said they would 'hook it up to the diagnostic machine' but then gave me only a vague "dunno!" as an answer!

Right...well what you have to look at now is what caused the cat to fail in the first place? If it was/is an HT fault as they 'think' then the chances are the new cat is dead now.

A T4 diagnostic is a diagnostic routine and healthcheck carried out on your cars MEMS ECU in times of ill-health. No, it won't detect a faulty/failing ECM, only specialist testing on a scope etc will determine a faulty ECM.

They really need to clear the basics out of the way and then start delving into the MEMS system.

Next query then. A friend of mine is a scrap dealer and believes it is possible to use alternate ECU's in different cars, eg. Mine is an MKC103020, which he says is difficult to source. Is it therefore possible to use another 'numbered' ECU in order to verify whether this is actually the cause of the fault?? (Ie by trying an MKC123?).:(

Well, it's not that straight-foward. Each ECU is matched to the alarm ECU on the car, preventing bolt-on diagnostics. You will need T4 to program the correct security code into the MEMS ECU to get the car started.

I wouldn't bother trying to fit 'another' ECU...you could end up doing more harm than good