aznwashed3

Hi Yall,

So im working on my friends 94 LS400. It came in with a very erratic idle and code 31. Cold start and when warm. I took off the throttle body and cleaned the crap out of it. I have never seen such a dirty throttle body. It took forever to get clean. I also took off the IACV and cleaned it too. I threw it all back together and it idles a whole lot better. At a cold start it idles fine, then as it warms up say about 2 minutes the idle starts to hunt a bit and throw the code 31. Then when completely warm at about 10 minutes or so the idle seems perfect. I need to hunt down this code 31. There is also TRAC codes 24 and 47 which are related to the sub-TPS sensor so i doubt it is related. Since it was throwing code 31 for "air flow meter signal" I decided to test the MAF with my volt meter. I tested the power wire and was getting (5V) "pass". Next I test the ground wire to the battery (POS+) and got (12V) "pass'. Next i set my volt meter to "Hertz" and test the "signal" wire while revving up the engine slowly and I got a higher reading at each RPM increase and constant reading at idle. "should be a pass as well". I don''t want to clean this MAF as it is ridiculously expensive and Karmon Vortex which I hear shouldn't be cleaned. SO I basically think even though its throwing a code 31 for the MAF signal, the MAF seemed to pass my tests. I heard that these cars often have ECU failure, but this ECU is newly rebuilt. I did pull the ECU out and open it up and everything looked fine. To sum it up, I did the following and I am still getting a slightly erratic idle and a fault code 31.Thanks in advance for any input!

-Cleaned throttle body
-Cleaned IACV
-Tested MAF sensor (constant, ground, signal)
-Checked ECU, although newly refurbished
-Sprayed carb cleaner to check for vacuum leak

LScowboyLS

I have opened hundreds of "rebuilt" ECU's - exactly NONE of them had the correct premium Japanese low-ESR capacitors as linked to in post #1 of my ECU capacitors thread

so rebuilt usually means a hack job using inferior cheap and incorrect components!


also, just cleaning the IACV is not enough, did you test the integrity of it's coils and bearings using the procedure from the factory service manual?

also, have you replaced the Engine Coolant Temperature Sensor (ECTS) - this is the one with two wires, and I strongly suggest you use the real one from a Toyota or Lexus dealership

Yamae

Your test for the MAF sensor was not enough.
Remember that the MAF sensor also senses the air temperature. Check the resistance between E2 and THA and confirm that the resistance is within the range.

aznwashed3

Thanks, I just tested resistance between E2 and THA. Looks like I am getting 2.27k which is within spec (2-3k). I guess we can rule the MAF out even though I am getting a code 31.

aznwashed3

I really had no idea about the poor quality of these reman ECU's. I would still like to rule out everything else before I determine its the ECU. I will pull the IACV off again find a service manual online for the correct procedure. DO you think this would throw a code 31? I have not replaced the (ECTS).

Lavrishevo

iTrader: (1)

I would replace or at least test the coolant temp sensor next. What abut the TPS? Oh yeah, and did you check for the wiring harness shredding in the trunk near the hinge? Common problem.

http://www.lexls.com/tutorials/EFI/tps.html

python

iTrader: (4)

[QUOTE=aznwashed3;7880736] I would still like to rule out everything else before I determine its the ECU QUOTE]

some people need to do more of this instead of going straight to...ecu issues
did this symptom occur before the ecu was fixed?
btw check ur tps as suggested
and recheck ur maf