m20b20 Weird vacuum plumbing?

[Module64]

Hi,

Engine runs silky smooth but sometimes it drops a little low at idle (500rpm) before it joggs it self up again to around 700 rpm. Im about to do a vacuum leak test when I noticed this weird plumping. Is this normal? If not, does anyone have a clue whats going on here?

Car is a 320i 1990 model

[TobyB]

Can't really tell from that picture...

is intake vacuum going to a thermoswitch on the housing,
then back to... something else?

t
needs better pictures.

[Module64]

Did some more testing. Here are som more pictures. T-split-hose connects to this thing on the hose that goes to thermostat housing, from there is goes to the valve(?) in the last pic. When engine is cold it starts oscillating between 500 - 700rpm for some minutes. If I remove the the T-split and take a hose directly from manifoil to fuel pressure regulator it stabilizes at about 700rpm instantly which makes me wonder what it's really for..

[TobyB]

Ok, that regulator (?) that the hose eventually goes to doesn't look stock...
...at least not in the US market.

Can you track down what the regulator's regulating? So far, what I'm seeing
is vacuum going to a temperature controlled switch, then to what looks like a regulator
of some sort. Which should have connections below it.

t
throwing snoballs at the ceiling.