M20B27 intermittant issue

[Wiglaf]

Right now this motor has 2 modes of operation:

1: runs as normally as a 300k motor can

2: runs so filthy rich that it won't even idle unless I unplug the AFM.

I'm kind of stumped on this one. At first I thought it was a vacuum leak but the elbow, hoses, usual suspects look ok. So I replaced the intake manifold gasket, valve cover gasket, vent tube seals. no change. In retrospect the intermittant nature of this should have warned me it's probably not mechanical. next?

-New coolant temp sensor
-tried spare AFM
-tried spare ECU
-O2 is unplugged
-tried without TPS
-tried without cold start injector

every time, car will come up, idle great in the driveway.. as soon as I go around the block it goes into asshole mode about halfway through, limp it back home with my foot 1/3 way down on throttle just to keep it from stalling.

When it's in this mode, idling with the AFM unplugged, I started probing around, wiggling wires, etc. Can't seem to find the culprit. AFM connector has 5V just fine. If I plug AFM in the car just immediately dies.

Any ideas??

[jlevie]

The engine's behavior with respect to the AFM suggests an intake leak. A smoke test will will tell if and where one is.

[thejimlab]

does afm flap get stuck open?

[Wiglaf]

putzed around with this again, checking grounds and stuff. Still runs like a top with AFM unplugged, the second I plug it in it goes super rich and dies. Tried spare AFM and spare ECU again. It never ran properly this time.. both AFM flaps are smooth and normal.