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Not sure about 88, but on a 90 you can only use the "press set 3 times" (type B) diagnostics if there was a problem that occurred during use of the cc. Those codes are lost as soon as the cc is turned off, they are not stored. Have you checked for type A codes, especially the speed check?

So, you are saying its cross counting as expected? Then the mixture is fine as the ECU is in fuel control. Seems unlikely though given a code 25. Suppose its true, then the next step would be to look at Vf and see how far from the norm you are running.

The Ox sensor should be switching between 0.1 to 0.9 volts and doing this rapidly (called cross counting). You cannot really measure this with a multimeter, you need a scope, or at least a meter with a frequency (Hertz) mode. The key parameters is not the voltage, but the number of cross counts...

I can see why it has taken hours and hours to get this far.

For another project in which the switch (actually keypad) could not be purchased, I resorted to soldering small gold plated shim stock onto the contacts. Has been working for 10 years since without issue.

The factory harness is all crimps, that should answer the question. Gas tight crimps are superior to solder for most applications. Still, solder can be acceptable, especially for high frequency RF connections. It takes professional crimpers to make a reliable connection. IDC connectors are...

The RC550s are fine, but they have two obvious issues that no one ever addresses. First, the turn on times vs voltage are different from the stock injectors, so this table needs to be recalibrated in the ECU code. Second, they draw a lot more current, and that means they are even slower than...

The ecu changes target idle speed very slowly. The surge is not from the ECU rapidly modulating the ISCV. You can get a feel for how slow it is by driving with a cold engine on the freeway until it warms up, then pulling to stop. The idle speed will be initially high since the ECU has only...

How did you validate the ISCV is not moving? I missed that note about it idling fine with the ISCV hose plugged, so it seems you have a metered air leak. Have you checked that the throttle plate is fully closing. If the ISCV is wide open it will idle fast enough to exceed 1600 rpm with a warm...

Depends what's wrong, but assuming your problem is that the ISCV is wide open all the time, then the throttle and TPS will be working properly and set no codes. You need to check if the ISCV is moving under ECU control.

It is likely your surge is linked to this. http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=FI&P=125

Can you hear your ISCV moving to the home position when you turn off the ignition? Interestingly, a disconnected ISCV will set no codes.

Ohms law, the missing link in your analysis.

I'm with him! What boost leak?

The rear bump stops for the 91+ cars are a lot cheaper from Toyota, and fit just fine on any year. Fronts should cost you $13 online each.

Oil drain plug leaking.... http://www.supramania.com/forums/showthread.php?10549-Oil-Drain-Plug&p=484646&viewfull=1#post484646

It needs to trigger off the first time derivative of the TPS position. I know nothing about AEM to tell you how to do that..

Whenever the ECU detects a throttle transient above a certain value it will fire all 6 injectors at once. It can do this midflight, so that even if a bank is on at the time it will still fire the others. Just one of many drivability tweaks in the stock ecu.

It's all in the book... http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EM&P=74

Most of the time you are running closed loop, so even with the code 52 you will not be running rich. Its only when you go open loop that it makes any difference.