My xj6 runs like it has a dead cylinder up to the point where it reaches about 2000 rpm, then as if I threw a switch, it purrs like the cat it is supposed to be. No clue what the problem is.
David

Many things come to mind, and some of my early thoughts are:

In no particular order:

Coils breaking down, and/or the wells they sit in are oil filled.

Very OLD spark plugs.

VERY grubby throttle body. You guys have EGR, we dont, and I read that is a major pain.

I will stop there for now.

Thanks, Grant
I have cleaned the throttle body and see no oil in the wells, etc. The thing that bugs me is the fact that at 2000 rpm it acts as though a switch is thrown and it runs as smooth as silk. By the way I was in Sidney and Cairnes in August. Would go back to Cairnes ANY time !!!
David

OK, god info so far.

YES, Cairns, VERY nice place, maybe my retirement eventually will see that be home.

I now awing to teh TPS, mounted under the throttle body, and barely accessable.

It gets contaminated with oily gunk that runs down the throttle shaft, thanks to gravity, and will give those symptoms. Since yours will be a 4ltr, and an electronic transmission, this TPS is also involved with that.

I have cleaned mine, successfully, BUT, mine being a 3.2 is not an electronic transmission (different TPS I believe). Others I read about have had little success with cleaning, and a new TPS is required.

If were mine, I would have a go at cleaning it. Off the car is the only way. Contact cleaner in a PP can is what I use. There are write ups here in the archives about doing this task, but it is not rocket science.

I agree with Grant that the TPS might be an issue. But before attempting to clean you should test it. Back probe the multi plug for the TPS. Check for Reference Voltage (5v), Ground and a variable voltage on the signal wire. The signal wire should give between 0.6v at idle and 4.5v at wide open.

If it's operating within these parameters look elsewhere. By not confirming your problem before you start messing about with things you may end up creating another problem and the whole issue just spirals.

What other checks have you made? I would want to look at fuel pressure at the rail. As a quick (and not definitive) test of fuel pressure regulator just pull the vac hose off it. If you get fuel out of the regulator (leave hose off for a good minute) the regulator is toast.