Oil in air filter box

[Carloz808]

Hi Everyone,
Just bought my first E30, a 1989 Cabriolet of ”athe Bay”a in the UK . 2.0 ltr 6 pot. A few dints and scratches but it drives OK. It appears I am only getting meagre MPG, having only driven it 100 miles. The mpg gauge when driving rarely goes off 12-15 mpg, and you can watch the fuel gauge go down quicker than a premier footballer. I saw a crankcase breather pipe was perished and replaced that as there was a bit of oil about and I thought I would change the air filter and plugs to see if it would improve. When I removed the whole air filter box unit , including ”aflow meter”a ( don’t know the correct name) , I noticed there was oil in the connecting hose and in the metal ”aflow meter”a , this dripped out with gravity when tilted . I even noticed there was oil around the ”abutterfly”a in the inlet manifold. After cleaning the butterfly with strong tissue paper, after moving it a few times oil appeared again, be it a few drops. The air filter was heavily contaminated with oil. I have not removed the plugs as yet as I ran out of time tonight.
Two questions. One should oil be there ? and is this effecting my combustion process ? Any ideas where the oil is coming from ?
Regards C .

PS forgot to say it is an automatic too !

[motormanmick]

Hello Carloz88,
my e30 318 had similar, from my understanding, there is crankcase ventilation and also idle control valve, mine had oil in both as well as the AFM (flow meter) carby cleaner in a spray can is the way to go to clean all these, if oil is in these, there will also be a dirty oily film in the intake manifold as well. The build up in the AFM may prevent the TPS from showing a closed reading to the ecu, build up of crap in the intake manifold means your injectors may be dirty as well and this will upset the spray pattern, it would be best to get them ultrasonically cleaned anyway if they've never been touched, that will include new "O" rings and filter baskets. Check all your hoses for vacuum leaks and your oxygen sensor for proper operation, also a full service is a great place to start and then work from there, cheers.

[Carloz808]

Thanks Motormanmick,
I will set some time aside over the weekend and have another look to make sure everything is clean and no leaks etc. Carb Cleaner Halfords ?

Regards C

[Brianmoooore]

Oil comes from the crank case vent. system, and some oil in the throttle body is normal, but nothing like the amount you seem to have found
This can be a result of a badly worn engine (very unusual) letting excess combustion gas into the crankcase, so a wet/dry compression test may be an idea.
Remove the cam cover (tappets probably need setting anyway) and see if there is sludge on the underside of it. There is a labyrinth, formed by the underside of the cover and a steel plate fixed to it, that is supposed to separate the gasses and oil before they go along the hose to the inlet tract, and if this labyrinth gets full of sludge, more oil will be transferred.

[Carloz808]

Thanks Brian, I will order a new cam cover gasket and have a good luck and as you say give it a good clean and adjust the rockers. What is the gap for the rockers ?

I am a newby to these cars so I will be asking many more questions,

Regards C

[Brianmoooore]

Clearance is 0.25mm, stone cold.
Cam cover gasket is usually good for a few uses without leaking. A bigger problem is the D shaped rubber bungs at each end of the cam box, in line with the rocker shafts. These go hard, and are a common leak source.

[bosers]

Welcome to the wonderful journey of e30 ownership. All great advice above, sure to get the glitches sorted! I would add though that these excellent engines aren't particularly economical, my 320i which ran really well only returned about 25mpg and was a manual. That was a lot of hills and lane driving though. My 325i consistently returns 22mpg avg! I do love it though!

[Carloz808]

Thanks for all your replies !