I have a 93 EG sedan D15Z1 Vtec-e. It is having a strange electrical problem. Any help or suggestions are appreciated...

When the engine is cold, no problems. As soon as the engine comes up to operating temp, the following happens...

Accelerating normally or quickly, no problems.
Accelerating slowly, as when stuck in traffic, as soon as you get to just over 1000 rpm and up to about 2500 rpm, the engine misses badly and runs on 3 cylinders. This only happens in 1st and 2nd gear. It gets worse when the AC is on.
When you change gears, just as you ease off the accelerator and the revs begin to drop, it flutters in the same manner.

I've replaced the rotor button and the coil. The leads check out ok measured with resistance and it has new plugs. All connections are ok.

The exhaust manifold has a leak. I'm wondering if this has anything to do with the problem as the cat is in incorporated into the manifold. If it's blocked, will this change back pressure and cause problems?

Does anyone know if you can get a set of extractors to suit this engine, aside from custom made of course...?

Any help appreciated.

Cheers