Hello everybody. I'm looking at my car and its high idle. It idles around 800 for the first 30 seconds to 2 minutes of running, then the idle creeps up to about 1500 when warm.

I just swapped in a b230ft from a 93 940t. Everything looks fine, except the idle is too high. There is also a little weeping from the thermostat area, which I think needs a little more torque.

So far, as tests I've done the following:
Clamp off (one at a time) the 6 or 7 intake vacuum lines, including the lines for the brake booster and the FPR and both from the charcoal canister. One of them dropped the idle about 100 rpms to around 1400 from 1500. It's the line to the breather box. Since it's a turbo, it also feeds to a hose attached to the tube running from turbo to intercooler. Unclamping it raised the rpms about 100 rpm. This was consistent.
Of interest - I installed the complete intake manifold I had before, including the FPR, injector rail, TB, etc. It ran (with a blown HG) before with a normal idle.

I pulled the IAC intake hose off the intake tube and plugged both ends. The idle didn't change much at all. Nothing definite.
Disconnecting the IAC makes the idle surge between 1300 and 1500rpm. Disconnecting the AMM makes the idle surge similarly to pulling the IAC, but faster. I cleared all codes after disconnecting both in one run.

The O2 sensor voltage swept like I expected it to. Disconnecting the O2 sensor dropped the idle a little. I did not try grounding it.

I pulled the temp sensor out of my old engine and heater it with a pocket lighter to about 105F. The resistance reading was 920 ohms. The reading from the ECU pin 13 to ground was about the same. This was a while after turning off the engine. Both old sensor and the engine head were about the same temperature - slightly higher than skin temp.

I sprayed carb cleaner on the top of the intake manifold gasket, and on each injector. None of those seemed to change the idle.
The throttle cable isn't holding the spool open. The throttle plate and idle switch are adjusted right, and it clicks every time I open the throttle.

So um... now what?

I'm going to get some dinner and a water bottle to spray on the intake manifold. The gasket I used was a thick grey, pliable fel-pro, not an Elring.

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1990 740 Turbo, on its way to stock specs, maybe beyond