B21FT 244 Turbo swap, now high RPM

1982 244 Turbo, manual transmission, well maintained.

I am going to have the turbo rebuilt for in the interim I just installed an old one I had acquired, I forget where or when.

Both are Garretts and seem identical except the spare one I just installed does not have water cooling, only oil (my regular turbo has both).

I changed out hoses as needed.

I've only fired it up briefly a couple times because although it fires up easily it immediately goes up to high RPM, about 3000 or more.

I verified that the throttle control valve moves freely and double checked for holes in hoses or bad hose connections: no problems noted.

Could it be that this turbo itself is causing the problem?

Thoughts / suggestions?

Try closing off the air bypass hoses for the idle motor to see if that air bypass is causing the issue. If it is there may be a bad constant idle system controller. Also if the constant idle system has an open circuit to the coolant temp sensor it may make a very high idle. Also check the grounds on the intake manifold as one of them is for the idle system. There should be one ground near the cold start valve and two more on the number four runner area of the intake manifold.

Also make sure the throttle switch is adjusted correctly. If the blade has become dislodged from the arm that sticks out from the throttle control lever on the throttl body, the car will run at 3200 rpm minimum. It'll act as if someone has jumpered the harness plugs to test the constant idle air valve.

Another thing to check is the harness that comes out of the firewall on the passenger side. It's for the constant idle system. The insulation on the wires is known to deteriorate. Quite possible that you might have a short between the four wires that get jumpered together, which means that it's testing the idle air valve at all times. If you can find a 49 state 1981 240 with the B21F, it will have an undamaged harness pigtail, stashed inside the passenger strut tower. Cut the pigtail off, ideally inside the passenger compartment, then, replace the same section on your car with the part from the donor car.

Thanks guys, I followed several of the suggestions and it seems to be behaving now.