Thanks, feeler gauges are here, waiting to check the gaps.
Will report back if the rough running is gone after changing the parts. But I have high hopes

 

Hopes were high, but after 90 minutes of changing the spark plugs and the coil the problem is still there.
there.The MIL is off now and there was only the P0300 present, but the rough/pulsating is still there.
I deleted the errors a 2nd time and started the engine, then the P0300 did not reappear though.
But it is still doing the pulsating.
Will try to unplug the O2 sensors tomorrow and test again.
Also I read that the crankshaft sensor might be faulty. Is that true?

 

What did your spark plugs look like, any symptoms of oil, fuel, or lean burn?

 

One plug had very slightly oil on the threads, the other looked fine.
​Maybe a little bit lighter/more white than usual but that might be due to the LPG.
I can take some pictures of them.

 

So I unplugged the O2 sensors now, went for a quick test drive, but still the same: when idling it runs a little rough, when taking the foot off the brake pedal it goes forward but a bit like a cowboy or something
No errors apart from the obvious "heater circuit" errors from the O2 sensors.

So, what else could it be?
Maybe the crank shaft position sensor? Or even the throttle body?
The noise and and "jumping" when the engine does it is very consistent. So that makes me think it might be some electrical problem, like the throttle body position sensor or something.

What do you guys think?

EDIT: The spark plugs that are in there are "Denso ITL16TT", so it seems these are "Iridium" spark plugs? Might these really be the cause for the error? Should I change them over for the stock Champion / NGK copper ones?

Here are the pictures from the spark plugs. Please note that I took the pictures a few hours after removing them, the oil was on the thread only and really not much.

 

Why do you post for help, and then ignore the answers? See post #8.

 

Sorry, where did I ignore anything?
Until yesterday, when changing the spark plugs on cylinder 7, I didn't even know what spark plugs there have been installed.
So if this is really a problem I will just change them over.
But I'm not sure why the misfires don't throw a code?

 

Oil on plug threads could be because plug was not torqued properly, or, oil is getting past the spark plug gasket. You may need a new spark plug gasket.
A bad PCV can also cause oil in the spark plug tunnel.
Did you notice oil on your socket when removing the plug?

 

No, there was no oil on the socket. Also the coil plug was looking clean without oil.

 

I ordered another 14 copper spark plugs and will install them when they arrive.
I also added some additive to the fuel for cleaning the injectors, as I read that they sometimes do have some problems and I had the additive around from my other car.

If this won't help I will have to get some kind of DRBIII-reader/tester to check for other culprits though.
I'm a bit out of ideas.

Tested it again today, on normal fuel at 1500/1600rpm and slight throttle it rumbles and vibrates, switching to LPG it goes away immediately, the moment I switch the LPG system on the problem is gone. Very very strange...