1992 Will Not Idle

[XL2007]

does the car stall out or does the idle drop to 200 rpms. idle is affected by the "air control valve" shown in the picture. it has two hoses attached to it one that connects to the air intake and another that is connected to the intake manifold. air flows thru these hoses and will affect your idle. if the idle is normal when the car is cold and drops when it warms up then this valve needs replaced. about 100 at a toyota dealer. if the car stalls out then you either have a vacuum leak or your tps adjustment is slightly off. lexls.com has the official method for adjusting the tps

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

the attached pdf shows the vacuum lines.

Thanks for the PDF diagram. I didn't see anything visually wrong with the trunk wiring, so that's been ruled out. I noticed that leaving the battery disconnected for more than thirty minutes will slowly reset not only the TRAC, but also the idle situation. A day after disconnecting the battery, the idle returned to normal, then edged up to a high 750-800rpm in Drive, and 1000rpm in Park/Neutral.

It stayed like this for a couple of days, until I needed to turn on the heater (cold snap :D ). I'm not sure if that's related or not, but the idle slowly fell until it hit 250-300rpm. When I got back in the driveway, it just died out.

I saw other posts pointing to the ECU as a possible culprit, among other things. What I will do is find another Throttle Positioning Sensor from another LS400 with TRAC and see if the symptoms continue.

[Lucky13]

Ive had that prob. Pretty much everyone who has that year has. Fuel pump fixed mine. Not throttle body, ECM ECU, Idle air controle valve, mass air senser. Although I replaced all of those before I figured out the prob.

[lexfourcam]

I had a problem just like this. I had a bad connection or a short in the wire that goes from the fuel pump to the ECM. Check the small stuff first. Don't dump a lot of money into it until you know exactly what it is.

[jcrome04]

You should at least try to clean the IACV.

[Lucky13]

And no reason to go with an oem pump should that be the prob. Go with aftermarket. Just not Bosch.