Working on a 75 1.8 with original fuel injection.
Engine runs okay at higher rpms, but runs very rough and rich at idle.
With engine running (stumbling at idle) if I take the oil breather cap off or remove the hose from the auxiliary air regulator the engine smooths out and idles up.
I have checked the temp senser and the auxiliary air regulator. Both are within ohm specs. And there are no vacuum leaks.

Any help would be greatly appreciated!
Jon

Check and see if the AFM has a stuck flap. If the engine ever backfired it may have a warped flap.

Thanks Clay for the response.
Yes, I have checked the AFM too. It moves freely.

Seems backwards to me. IIRC when I removed my oil cap the car wants to die. But maybe my memory is backwards. So much has been wrong with my car, I just usually have to ask....

I agree, most likely a issue with the airflow meter, check that first. We recently had a guy with very similar issues as yours, his ended up being a bad ECU.

crap! I forgot that one.....

A 74 ecu is wired different from a 75. If you put a 74 ecu on a 75, it will run way rich. If you put a 75 ecu on a 74 harness, it won't run. The AFM wiring is different.

Check the number of pins on the AFM connector. It should be 7 on a 75. And if you need a 75 ECU to try, I have one.

It's actually a 7 pin AFM off a vanagon (according to the part # on it). Not my car, working on a friend's. Lol
But it was running great before taking engine out to replace throwout bearing. It's like something isn't hooked up properly, but I know it all is.

Check the connector where the CHT joins the injection harness. That is prone to being improperly connected, and it will run full rich if disconnected.

Checked the CHT connection and the senser too. Senser has 30 ohms...

And you think 30 ohms is within spec?

Oops, my bad. The CHT is 288 ohms. The auxiliary air regulator is 30 ohms.