I've been having problems with my '99 Magna TH Sports this week. There seems to be a bit of missing on tickover but only slight, however sometimes when accelerating it can be obvious and there's quite a lot of stuttering. The engine warning light is also on so thought that instead of guessing at each possibility I'd do the right thing by earthing terminal 1 of the diagnostics port, turning the ignition to "on" and reading the number of flashes. However when I do this it doesn't give me any codes, not even code 0 (which would mean that its okay). The light just doesn't flash.

It can sometimes be worse than others so its not always the same.

Any ideas would be welcome.

On tickover? Not sure what that means.

How old are the leads and plugs? That can cause issues with missing.

So the engine light comes on with the car running?

Tickover means when it's idle, not sure how old the leads and plugs are
and yes the engine light comes on when the car is running, starting to think that its computer since the light doesn't come up when doing diagnostics and the manual says if the light stays on or not at all then its faulty

check the MAF

MAF checked, got another one, cleaned it up and put it it
also cleaned the idle air control valve and the throttle control

The car runs on gas and petrol, though the petrol side of things doesn't seem to work at all

http://i.imgur.com/pgb9bFq.png
unplugging this doesn't seem to do anything, anyone know what it does? maybe it's the culprit
the hose is from the converter and runs to the engine, I know its a sensor but I'm not sure what it's purpose is

Solenoid controlling hot engine coolant flow to the gas converter?

Someone with gas needs to chime in though.

So running ok on Gas and not Petrol, that is where you start then

LPG cars are well known for fuel system issues as the fuel just sits there for ages, if you pick up damp fuel (ie with water in it) then you will most likely have rust issues in the system. We fix a few of these and it does get expensive