Having some Troubles...
 

Ok let me throw it down for ya... so i have a rebuilt and the check engine is light and the codes are 27, 51, and 52. Ok before i rebuilt the engine, it was giving me 52, and 42. i checked the wiring and replaced the tps, and knock sensor. (used) and nothing so i took the ecu to get checked and they said it was ok.. it seemed fishy, so i went to the junk yard and brought home an ecu from an 87 n/a auto. the car idles smooth, but throws those 3 codes. I connect the 87 n/a mt and only 2 codes set, but idles really bad! I was thinking that maybe by getting the correct ecu, and knock sensor might help. PLZ HELP ME!


SPECIAL THANX TO ThOSE THAT HELP!!!

First of all, the ECU's rarely go bad on these cars so I would rule that out without checking the sensors first.
By looking at your info your from fullerton which means california and an M/T means you don't want to put an auto ecu on there without mods.
California has an extra oxygen sensor on the cat I beleive so you have either a modded exhaust and disconnected the sensor and the UCU isn't getting feedback from the oxy sensor or its bad and your ECU is sensing this.
I don't know the subtleties between the different ECU's
except the color of the plugs on 86.5-88 are yellow and 89-92 are grey.
It is possible that the one you put in is 89 or later and causing it to run bad. Check if the plugs are grey and try plugging in the yellow plugged one from a 86.5 -88 M/T, clear the codes and see if they come back and see if the idle smooths out.
I'm not sure if there was a special ECU just for california or not.

well my car only has one oxy sens. For a fact I dont think that my exhaust is modded cause when i first had this car the check engine light would only go on when i would go past 35 rpm. I changed the Knock sensor twice, and the tps like 3 times. When i pulled out the engine i also checked the harness, followed the cables from the tps and made sure that there was resistance. i replaced the tips cuz they were crusty. Forgot to mention that the sensors i got from the junkyard! Like you say: The ecus rarely go out on these things. but what trips me out is that the car idles fine and runs great with the Auto trans-The ecu connections are gray. I believe i got them from an 88 month 8 meaning it was 89. Just today i wnt to the Yard and didn't find a single mk3, only 2 mk2 and a butt-load of cressidas, which both are no good for me. I'm not giving up!!! Now that you mention that... I just now understand what you were sayin bout the second oxy.. the ecu that i got(auto) is from a california emissions and therefor has a heated oxy. the second one, and my car only has one oxy!
Dude, thanx :dance:

When you put in your TPS did you 1) Get the right one, and 2) Set it per TSRM? There are two (that I know of) different TPS for the MKIII Supras, one plastic and metal and one all plastic. The rotating piece on the inside is 90 degrees different from each other, so I would verify that when your TPS is installed that your throttle body actually spins the inside of the TPS. After doing that, look up in the TSRM the resistance Specs for the different check points on the TPS and make sure they're in spec, otherwise you'll keep getting that code.

The IDL code is probably set by the TPS being out of rig. You can set it as per this page in the TSRM.
MK3 TSRM On-Line

The Knock sensor is a coax wire that could be shorted or open somewhere, You can read that from the ECU to verify the wire if it is shorted and from the ECU to the plug end to verify the wire has continuity from the ECU. I don't know how to physically check the sensor to see if its good so basically all you can do is to check the wire. That area gets alot of heat so there is a chance that it has become brittle over time and just removing the plug could have inadvertantly broken the signal wire. There is a "How to" rewire the knock sensor here and more info on the sensor itself. The turbo has 2 btw so ignore that part of the writeup, the NA's just have one.
Knock Sensor Rewire