car wont rev over 3k.. and what is this part

[skater335]

i have an 84 318i that i bought about 2 months ago as project car. I have a 335i as my daily driver. 2 days ago i decided to take the 318 out for the day and it ran great... about an hour later the car slowly got worse then all of a sudden it lost power and wouldnt let me go past 3k rpm. Sort of like it went into limp mode. when the car is cold it wont idle it just dies unless i give it a lot of gas to keep it ideling. once its warm it wont rev past 3k and makes this loud skretching sound till it warms up.kinda sounds like a belt squeal.
so far
-checked for vacuum leaks
-tested for continuity of the tps
-changed the fuel filter
-checked the afm
-changed and checked the plugs
-cleaned the icv
-any more options?
i found this box next to the afm and it seems to be missing a cover to it. It has power flowing to it. heres a pick of it


it looks like the cover to it fell off. seems to be the problem bc when i touch it with the multimeter it causes the car to almost stall out when its warm.
thanks for the help!

[E30_Pare]

hmm never seen that part before in my 85 318i. maybe check your dizzy? you've already covered most of the bases

[skater335]

dizzy?
ive searched all over and in my chiltons book and there not even a picture of it online or in there. and cant find it on realoem either.

[Danny]

Distributor cap.

[jeffw]

is that connected to your airbox?

[skater335]

hmm ill have to look at the cap.

and it is bolted to the side of it with a plug into the bottom of it.

[FetusGoulash]

that part is a tricky one. mine was missing the cover as well and searched for a while. it is for relative air pressure i believe. Underneath that black plastic there is a (what looks like) a bi-metallic coil which i assume changes tension or shape at different elevations and changes afm. I removed mine and it had no effect. I am at sea level though if it makes a difference, and only ever travel to about 400m above sea level here

As for the RPM thing, because it has an issue when cold i would suggest checking the coolant temp sensor. i believe it will be on the coolant manifold at the front drivers side of the head. does it have trouble with cold starts?
next would be to replace fuel filter, then pump

[skater335]

well it never had an issue before till i drove it the other day. now when i start it it dies a few times till the car warms up enough to idle on its own then it wont allow me to rev over 3k and there is no power. when i rev the car from under the hood it makes a deep throaty noise like its trying to rev but something is holding it back.
Ive already replaced the fuel filter but i dont see the fuel pump being the issue since it stops right at 3k and the gas dosent cut in and out.

as far as the little box goes im not sure... when i unplug the bottom of it the car wont even start it just sits there and cranks... so im thinking it has to do with something with more. Ill take a pic of the bottom of it and the plug as well.
thanks

[skater335]

hey fetusgoulash you were right it was an altitude sensor. good call. thanks for that. im going to take it off the car. do you remember what you did to remove it? seems to be some wire to it