Trac Light -Check Engine

[bigo]

I have a 93 ls400 that starts good, idles good, until it reaches last step of idle down at about 650 rpm. It hesitates a bit then the check engine and Trac-off light comes on, with the computer reading a code 31. If I speed up the engine to 1200 or so the lights go out. I took the throttle body off and cleaned it good and it still acts the same.Checked and cleaned all electrical connections, also made sure all vacuum hoses are tight, took off EGR valve cleaned it, not very dirty. Tell me its not the MAF that code 31 says it could be! What troubles me it runs great until you let it idle then the lights come on even though it idles fine.

Thanks for any suggestions

Bigo

[steve2006]

It could be the MAF sensor but the engine management light normally comes straight on at start up when it is faulty without touching the throttle,with the idle problem and assuming you have traction control fitted it could be one of the two throttle position sensors attached to the throttle body,if you have a digital multimeter you can check the output voltage to see if it rises and falls without glitches when the throttle is operated,if the meter shows an unstable voltage at any point it could be a bad track on the TPS,unfortunately they are sealed units so cannot be cleaned.

[bigo]

It could be the MAF sensor but the engine management light normally comes straight on at start up when it is faulty without touching the throttle,with the idle problem and assuming you have traction control fitted it could be one of the two throttle position sensors attached to the throttle body,if you have a digital multimeter you can check the output voltage to see if it rises and falls without glitches when the throttle is operated,if the meter shows an unstable voltage at any point it could be a bad track on the TPS,unfortunately they are sealed units so cannot be cleaned.

My Lexus manual gives a procedure to check out the sensors, sounds like a reasonable idea. Thank you for taking interest.

BIGO