Hi guys, I have a '98 LS400 and I usually don't use my AC and just cruise with all windows down but today, I decided I had enough with the hot weather so I turned the AC on. Didn't blow as cold as I wanted it to even on max cold and my idle started fluctuating whenever I came to a stop. It's fine while I'm driving or when my AC is off.

On the same note, my car NEVER idles above 1k rpm even on a cold start. Is this normal? I have about 170k miles on the car. The highest it will ever idle on a cold start is exactly at 1k rpm.

Where do I start? Should I clean my IACV first and see if it fixes the problem or is this an AC compressor issue? Haven't changed out my cabin air filter yet either but don't think that would affect idling.

 

Could also be a very dirty throttle body. If you have never had it cleaned I would certainly suggest it. Even in Puerto Rico, where it never gets below 83 degrees my 99 will idle at about 1300 RPMS on a cold start and settle down to about 800 pretty quickly. With AC on I idle about 650 in gear. With AC off I am usually about 550 in gear.

 

clean throttle body.

 

thanks guys, and indeed it was the throttle body! it was very dirty and needed some good ol' cleaning. now my idle is back to normal. i plan on cleaning the MAF sensor soon as well.

 

Glad you got the idle cleaned up.

Be wary, read my comments on other threads regarding MAF cleaning.