Pesky misfire leaving me baffled

[jamie.91]

Ok guys, 172 cup, started a while back with suspiciously lumpy idle, gradually got worse, now has a pretty constant misfire when accelerating, low gears at low speed as soon as you put the engine under load there's a rather bad missfire then after 2000rpm ish it pulls like it should.
Car is well maintained and looked after, has standard airfilter set up, plugs less than 1000miles ago, never had any other problems.

Poverty spec obd scanner shows a p0300 code which just relates to a missfire but not cylinder specific

Few days ago I swapped the inlet manifold with my other 172, including throttle body,map sensor and so on, I also put a new o ring on the cam breather thing. Also swapped coil pack and HT leads.

Made no difference
So whilst swapping back I pulled the plugs, cylinder 4 plug was black/badly fouled.

Cleaned said plug and swapped with cylinder 3 plug.

Whilst this far in I swapped the fuel rail and injectors as a bad injector was a possibility I figured.

Covered almost 100mile in the car tonight and it's the same again.

Gonna pull the plugs again tomorrow and expecting to find cylinder 4 plug fouled again.

I was going to start swapping o2 sensors but I doubt it's that now after seeing it's cylinder specific.

I'm running out of ideas so any help appreciated.

Thanks guys

 

[ForceIndia]

I had similar (years ago). Turned out to be lambda.

 

[jamie.91]

Wow really? That was next on the list to change until I saw the cylinder 4 plug, surely lambda can't cause a cylinder specific problem?

 

[bloke]

even on cheapy obd reader lambda can't bring up a misfire. get it plugged in to something decent and take it from there.

 

[jamie.91]

I'm struggling to find someone with clip that does call outs

 

[bloke]

i stopped going out to do jobs years ago, pain in the backside as you have to take all sorts with you 'just in case' and then there's always something you need that you haven't brought with you!!