Why does my '74 1.8 sometimes run so RICH?, After a bit of driving, it won't idle Options

[drdstny]

Hello many kindred,

So I drive my 914 every day, about 60 miles per day to be exact. Almost immediately, I noticed that (this is so hard to believe I'm having trouble posting) if the left engine heater hose comes off the heater blower, the car won't idle and will stall unless I keep the R's up above 2K.

So...I fixed that with some Tape.

Before I Taped it to the blower, it was predictable: if the car suddenly started running rough, rich, with smoke pouring out of it, then I knew I needed to put the hose back on.

Since I "repaired" the hose, now it's less certain. About halfway to work, once I hit traffic and have to stop-n-go, it idles rough. VERY rough, and I need to side-step the gas to keep the engine from stalling. Smoke will come pouring out of the tailpipe, my eyes water, can't breathe, lose faith in humanity, diet goes awry, idle won't calm down...you get the idea.

Seems like it only does this after about half an hour of driving, and USUALLY letting it sit for a couple hours will make the problem go away. Not always, but usually.

The first thing I tried was changing both seals (O-ring and gasket) on the oil cap (recall it's a 1.8), but that made zero difference.

So...anybody have any idea what's wrong? Just as good: anybody have a list of things I can test or replace until the problem is fixed?

This is a serious issue, and the last two tanks of gas have been sub-20MPG so I'd really appreciate the help. I'll send something nice to the person who gets me out of this jamb.

Thanks!

[Dave Bell]

Airbox = AFM... what everybody said above...

If vane sticks in AFM, when you return to idle, vane is still open as if you were pulling more air through so FI pours in more gas...

AFM gone bad from old age or wacked with too big a hiccup that went backwards through the intake. There is a spring loaded port on the vane to protect from such back fires.

You can acutually, "catch" a sticky AFM in the car... when you are running rich at idle... stop the car...

Method #1: Then turn the key on but do not turn the engine over... fuel pump should NOT come on.... Fuel pump on the L-jet only comes on when the AFM vane comes off the closed position, i.e. when you are cranking the car... if the vane is stuck open, the fuel pump will come on with engine off but key in on position... if this is the case for you.... wrap/tap on the side or the AFM to see if you can unstick the vane... if it unsticks and returns to closed position, fuel put should go off.

Methond #2 Take out the AFM and see if it is stuck partially open.... or just take out the AFM, move the vane by hand and see if it sticks somewhere along its travel..

Bad CHT or disconnected CHT will make you run real rich... FI thinks the engine is super cold and pours in the gas.

Fuel pressure regulator would have to be pretty far off to make you run so rich it would hurt your eyes