1981 308GTBi idling at 3000RPM until warm

It would be in your Aux. Air Valve. Check your jumpers again as that would do it. I have jumpered my 83' for years to stop the cold start, high idle.

 

The AAV is open when cold and lets additional air into the plenum. As the engine warms up it gradually closes, it does get 12V. Here is a pic a friend sent me. It should be on near the plenum on the right side.

 

I should clarify that on your car there is another component besides the AAV that helps control the Vacuum. The AAV will look just like that but without the extra vacuum ports. Unplugging it won't solve your problem. Jumpering should work. Check them again and clean the contacts on the jumper wire. The AAVs can stick. Mine has. You can remove them and check the operational condition of it. It should be open, put 12V on it for a few minutes and then it should fully close. You can clean them if they stick. Carb Cleaner and brake cleaner are good choices.

 

Well replacing it instead of cleaning it would be the next option. The other device is something like a Vacuum limiting device or ?. I don't remember the name off hand. Not sure how to test its operation. My 85' QV uses a slightly different setup and just uses the AAV.

 

By "checked" do you mean that you measured the electrical resistance from one wire to the other at the other end wherever these two wires go?

Another option might be to look at things directly at the cold-start air valve itself (which is what you're trying to disable by shorting those temperature switch input leads anyway). Always hard to guess how the logic works on these gizmos, but at your next cold start you could try:

1) remove the small rubber vacuum line going from the electrovalve to the cold-start air valve (and block it with your finger or an appropriate plug) leaving the vacuum nipple on the cold start air valve open to atmosphere (i.e., no vacuum present) -- if this drops your cold start-up RPM this might be a more reliable way to disable the cold-start air valve (i.e., forcing the output state you want rather than trying to fool the input conditions to create the desired output state).

2) If the cold start RPM is unchanged when doing #1, try hooking the small vacuum source line going to the electrovalve directly to vacuum line going from the electrovalve to the cold start air valve (i.e., putting vacuum directly on the cold start valve during cold running).

Alternatively, when running warm idle at 1000 RPM if you remove the vacuum line from the cold start air valve (and block it with your finger/plug) and the idle RPM is unchanged then you know it works ala #1 (i.e., no vacuum = closed cold start air valve). If the warm idle increases when you remove (and block) the vacuum line at the cold start air valve then things work ala #2 (no vacuum = open cold start air valve).

Just some guessing...

(Fig 60 page 68 of OM 216/81 shows the cold start air valve, the electrovalve, and the vacuum line in-between)

 

I forgot to put the vacuum hose back onto my injector manifold after my first oil change - same symptom. Realized what I did immediately. You may have a leaking vacuum line. Maybe it is an easy fix.