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Idle Problem With My 1990 Lexus Ls400 Please Watch Video


MrWinkle
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Hello guys and gals, I have been having this issue with my 1990 lex ls400 for about three weeks now. I took off the throttle body, cleaned it, and the intake and i still have this problem. Do you think the throttle position sensor is the culprit? PLEASE WATCH THIS VIDEO BELOW. It will explain it a whole lot better than me. Thanks in advanced

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Check all your vacuum pipes and the IACV. From the video (good idea BTW) it looks like there is insufficient air flow at idle so the engine stalls,the valve is located on the front of the plenum chamber to the right of the coil.

2nd post on link may help

http://us.lexusownersclub.com/forums/index.php?showtopic=42315

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Ditto dirty and/or sticky IACV and or vacuum leak on intake ducting after the MAF.

I'd start by removing the IACV and scrub it down good with cleaner. Lubricate moving parts and make sure it isn't binding.

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I don't think you can rebuild them replacement is the only option,another possible cause could be the the TPS.There is a switch in the unit which activates when the throttle is fully closed (idle position) the switch then sends a signal to the ECU to inform it the throttle is closed which should then result in the IACV opening to supply the idle air supply,if the switch is faulty it would cause idling problems.

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This could get expensive if you just start throwing parts at it. The IACV is a pretty simple device. An electromagetically actuated valve. If you search the forum there is a test procedure for checking the coils. It just takes a simple ohm meter. You don't want any coils to be opens or shorts.

The mechanical test is visual. If you can move the valve with your finger and it isn't binding it should be ok. If its sticking at all clean and lube. Repeat until it moves freely.

Here is a cleaning tutorial: http://www.clublexus.com/forums/rx-first-generation/358579-diy-iacv-clean-picture-write-up.html

Testing and bearing replacement.. http://www.planetsoarer.com/IAC/iac.htm

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Okay, check the codes and now the plot of this story has taken another turn. I got code 13 - RPM signal no. 2 and code 52 - No. 1 knock sensor signal. Now the check engine light has been on since i bought the car, I had her timing belt and water pump changed but she ran fine up until now. So does this rule out the TPS and IACV and have the cam sensor and/or knock sensor signal been behind this the whole time?

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  • 2 months later...
  • 2 weeks later...

dang, that happened to my mom's car and my car when I changed the water pumps on ours, hers a 94 mine a 92. It turned out on her I forgot to plug the MAF sensor back in(I know, dumb) but it ran almost exactly the same and also I had put the passenger side rotor on backwards. So maybe you should check those but since you said it ran good for a while it might not be. My car the 92 what had caused the rpm signal 2 code was i guess some water got in the coil on the top, thats the rpm signal 2, the coil went bad so i replaced that fixed that code; then, the knock sensor was when i had reran the knock sensor i didn't hook it back under the coil which caused the serp belt to rub it and eventually cut the wire so i had to go to pick n pull and get a new after that the idle went back to normal on both cars and ran fine. So to recap check the MAF sensor, make sure the rotors on correct, check if knock sensor wire is cut and replace coil if needed

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