M20 engine misfire and limits at 5k

[lanceyboy]

Hi guys,
in need of some help here...
my 320i developed a misfire a while back and so got straight on the case, the symptoms are cold start lumpy idle/hunting, missing all the way up the range. when warm, revs freely enough although can feel holding back and will not rev over 5k and my fuel consumption is beyond belief averaging 15mpg!!!here's what i've done so far.
new plugs,checked all Ht leads for breaks and also checked for sparking on all plugs(ok), new fuel filter, checked all injectors are firing and checked ther ohms readings(within manufac spec), had dis cap off and cleaned up points and checked for moisture.
after all of the above being changed or being in serviceable condition i was led to the AFM as the new plugs were fouled within a few mins of running so I took the AFM off cleaned it out and adjusted the screw this resulted in it running too lean and issue still remained so i've since replaced with a 2nd hand unit and a 2nd set of new ngk plugs and the fault stll persists although is sumtimes a little better but fuel consumption is just as bad, engine still holds back and fuel consumption hasnt changed one bit. I have supected that maybe rings are worn but have not yet checked compression and there are no signs of oil coming past the pistons.
hopefully someone has experienced a similar issue as i am at the end of my tether with this one haha
cheers guys

[lanceyboy]

its the motronic system. tried sucking the vaccum hose and nothing at all. bloody nightmare this

[Wocka]

I had a slightly similar fault, the car would misfire at 3-4K when cold and 5 when on track, got worse in the wet.

Turned out to be the leads, bought a 2nd hand set for cheap on here.

Is it still running lean after the new AFM?

Edit:
Have you checked for air leaks on the inlet side? particularly around the MAF.

[lanceyboy]

checked for air leaks but nothing stands out, it hunts only when cold and once at temp it idles around 800 quite happily although like i said at the beginning cold or hot it wont rev by 5k and can feel it holding back through the rev range. i checked the leads again tonight but no issues there, pulled them off 1 by 1 while running and could hear it jumping on every lead.
well the afm lean running was caused by myself, had adjusted the screw too much so tonight i turned it 3/4 out from a seated position, ideally i should use a meter to check the emissions but unfortunately havnt got 1 so its a trial and error with the screws positioning

[Wocka]

have you checked the blue temp sensor?

[TouringMatt]

The HT leads will only show problems under load i have found, once put an aftermarket set on and it would drive ok, but when i tried to accelerate up a hill it would jerk and misfire badly, put the old OE leads on and all was good

Cold running - try the blue temp senser but also check the wiring plug that sits under the inlet manifold ( bit of a bugger to get too ) i spent ages trying to solve a cold running problem, turned out to be a break in the wire that runs to the blue temp sensor

Hope this helps

Matt

[lanceyboy]

thanks for that, i'll check sensor tomorrow. I checked compression tonight 5&6 were way down at 125-130psi and the rest were up at 150+psi,could this have any affect?definately the rings as I checked again after putting some oil down bores of 5&6 and comression rose to 150+psi.
I think i'll also try and source a set of HT leads this week.
cheers

[lanceyboy]

I noticed today that if I - instead of giving the car utter stink - nurse it gently through the rev range it will go past 5k, it only seems to be limiting at 5 when you give it what for, any views on this?
regards
Lance

[Wocka]

Sounds more like leads to me

[lanceyboy]

I'll try get a set this weekend, thers a local e30 breakers 20mins from me so i'll pop in there on sat. cheers