'91 Ls400 Rough Idle

[1991 Lexus LS400]

Hi Fellow LS400 Owners,

I have a '91 LS400 and have about 230,000 miles on it. It's been a great car (I'm sure that you all agree) to me and I have owned it since 1995. I ran into rough idle/stalling at low speed issue about two years ago. My mechanic cleaned the throttle body and it did not lick the problem. He then suspected that the MAF meter was broken and we replaced it. It did not work either. Finally, we found out that one of the connecting pins to the MAF (there are five in the cluster) was loose. We fixed it and the problem went away.

Yesterday, my car stalled again on the freeway in a stop and go traffic. I pulled off the road and waited a few minutes and was able to get going again and I limped home with one foot on the accelerator and another on the brake at stop light. When I got home I read a thread on the RX300 Forum (http://us.lexusownersclub.com/forums/index.php?showtopic=30723) and went ahead and performed the process per the detailed instructions. However, the '91 LS400 throttle configuration is different from the RX300 pictured in the instructions. Nevertheless I was able to basically clean out the throttle body although I could not find IACV. Here are my questions:

1. Do LS400's have IACV and if so where is it located?

2. After I performed the process my car idles fine but the idle feels a bit rougher than before, any idea why?

3. After I put everything back together I found there is a black metal ring left . It's about 3 inches in diameter, 1/16" thick, and 1 inch wide. Where does that go? Is that related to rough idle issue?

Thanks everyone for your advices.

Best regards,

Ray

[1991 Lexus LS400]

I found the attached shop manual on ICAV removal, inspection, testing, and installation.

index.pdf