M12 threads? That's huge!

10mm will probably be a bit long, they need to be roughly the same as the thickness of the manifold where it is drilled. You don't really want a length of the bolt sticking into the intake obstructing the airflow. Might be a good idea to take one of the spuds out and see if you can gauge the length you need.

No need to drain the coolant, you'll lose a bit but not a lot, just take the Tee's out (assuming it has been plumbed in parallel with the heater) and replace with straight joiners (or replace the complete hoses with new). The spuds into the manifold will be M6 (normally, or they could be M5) thread so all you need are some very short bolts with a dollop of Hylomar on the threads. That will both act as a thread lock and make sure they seal. I run a single point system on mine but drilled my manifold years ago while it was off in case I ever wanted to change for a multipoint and Hylomar coated bolts have sealed the holes for years now.

Wiring might be a bit more complicated. It will probably have a tap into the Brown/Yellow wire that feeds ignition switched power to the fuel injectors, another one from the TPS feed and the injector cut wires. Just occasionally, the installer will also have connected into one of the lambda sensor feeds too but most don't. The feed from the ECU to each petrol injector will have been cut and a pair or wires connected to intercept the pulses from the ECU to each injector (these intercepts will be a colour and the same colour with a black stripe onto each injector feed), so you will need to remove those and reconnect the feed direct from the ECU to the injector.

If you look at the multivalve on the tank, it will have a knurled knob on it somewhere. That is the shut off for the output in addition to the electrically operated solenoid valve, so screwing that in will isolate the output from the tank.

I know the early base spec ones came with cloth seats but not sure about the later ones..It wouldn't have had electric seats though. Are they the full electric with the up down, forward and back buttons on the side or just the basis electric with only up and down? No sunroof isn't a big deal as long as the AC works, so I would suggest getting that sorted. It might just need re-gassing but if it has a leak chances are it will be from the top right corner of the condenser. The factory sat nav is so out of date these days that not having it is a bonus. It may have the low line audio system (no mid range speakers in the doors) which means it won't have the door amps so any standard head unit will go straight in and just work.

It all sounds much like the MAF, all sorts of strange things can happen if they are iffy. Sometimes they won't start at all, other times they will start but not rev unless you keep pumping the throttle, other times they appear to start and run normally but misfire when under load and it sounds like you've got a mix of all options. Genuine ones are still available but at around a grand a time, I doubt many people buy them (which is probably why they are still available) and aftermarket vary wildly, some work OK, some work but give really odd outputs while others just don't work at all. Secondhand original are a better bet.

17 steps is a touch low, optimum is between 15 and 30 but it should be OK. When the revs drop, the stepper opens up to try to increase the revs back to where they should be but for some reason, it isn't doing it. What is a bit weird is the MAF as at the lower revs it should show a lower airflow not higher. When it is idling lumpy, what happens if you very slowly open the throttle? Do the revs climb steadily and the misfire clears or is there a hesitation at the just open position?

See what different diagnostics show and go from there.

Ahh, no doubt the vacuum reference so the LPG pressure would have been all over the place.

There's not many people that haven't had queries about the EAS, it's black magic until you get you head around it.

That's low, have you replaced the fuel filter? I probably confused things a bit with my last, higher intake vacuum at idle will result in lower fuel pressure and with the throttle open there's less intake vacuum so the fuel pressure will stay high. If the fuel filter is clogged that could explain why it is OK for a few seconds upon dropping to idle and then start missing. It is likely to be running lean most of the time so after a run the fuel trims will have gone positive to correct it so it is then rich next time it is run.

What was your original login? What's the LPG problem?

Depends what scanner you are using on it. The GEMS is not fully OBD compliant but OBD2 only understands 0-1V Zirconia sensors and not the 5-0V Titania ones we have so a generic scanner will often translate the 5-0V signal into the equivalent 0-1V where 0V is lean and 1V is rich. I've got a Nanocom which shows the readings correctly but I've also got a Launch CReader (V or V1) which translates the 5-0V into 0-1V readings and I think, but can't be certain, that it does show them the correct way round (showing 0V for lean and 1V for rich). Correct MAF readings are 20 (+-3) kg/hr at idle, rising steadily to 61 (again +-3) kg/hr at 2,500 rpm. Fuel pressure should be 34-37 psi but with reference to intake manifold pressure so will vary with throttle depending upon how much intake vacuum there is (higher at idle, lower with throttle open).

Look at the fuel pressure on the Schrader vlave on the fuel rail, you don't need anything clever, you can use a tyre pressure gauge. With it running, look at the O2 (Lambda) sensor outputs. On a GEMS they are 5-0V sensors with 5V being lean and 0V being rich and should flip-flop between the two limits. If it starts missing the problem is usually it going rich, so you would be looking at the sensor voltages going to 0V. Also look at the output from the MAF sensor and see what that is showing you. If you have replaced with a pattern part, they often give really odd readings.

What's the fuel pressure and does it droop when the misfire starts? 110psi is low on all pots but it still shouldn't cause a misfire, it will just be a bit down on power. About the only thing you haven't changed is the crank position sensor but they normally work perfectly OK until they get hot and then they die completely. Do you have diagnostics that can show live data?

Last time I changed one I tapped the cold chisel into the slot and left it there while putting the spline into place so it held it open. Once it was in I then pulled the chisel out and put the pinch bolt in.

Not sure it is but opening it out a bit with a thin cold chisel allows it to slide on easier.

If it is coming out of the little vent hose and not the exhaust silencer, that would suggest a problem with the diaphragm valve. Has the valve block been apart?

Or just bungy it to the gear lever. Yes, the steering wheel is heavier at one side so if you don't tie it, it turns all on its own as soon as the column is disconnected, Then you've got to try to get it back on in the same place or your steering wheel is on the piss and there's a danger of buggering up the clockspring thing.

More a don't skimp on an expensive car, particularly when we can charge £3 each for 50p copper washers. Yes, they are standard banjo copper washers but when I changed my steering box I reused the ones that were on it and they don't leak.

Make sure the one you've got to go on is complete with the Pitman arm as taking one of those off needs about 4 people to hold it steady while someone else belts it with a sledge hammer. RAVE says to take the washer reservoir out but I found that undoing the securing bolts and shoving it forwards gives enough clearance. Tie the steering wheel where it is as it will turn when you disconnect the steering column at the steering box. Don't have the steering lock on or there will almost certainly be tension on the splines so it won't slide off easily. Give both splines a good dosing with Plug Gas and a small tapered chisel in the slot increases the chances of it coming off. I used a wedge type ball joint splitter to get it to start moving away from the box. Destroyed the plastic ring with the centre marks on it but as it was scrap anyway it doesn't matter. A simple enough job even if it is bloody heavy and a bit awkward.

Out of balance front wheels can be felt through the steering, but with rear wheels you don't feel a lot through the steering wheel, you feel it through the seat of your pants.

What makes you think it is the rear propshaft? Out of balance rear wheels tend to hit resonance around 55-60 mph (88-96kph) and that can be felt through the whole car.

Exhaust solenoid or clogged exhaust filter?