Hello, new to this forum stuff I recently bought a 92’ LS400 and for the first few months it drove like a dream, then one morning I started it up and had an incredibly high idle it hovers around 1700 RPM now. I cleaned and swapped the IAC also cleaned the throttle body it improved my symptoms for a few minutes then went right back to idling high. Anyone have some insight on what could be my issue?

 

hello, and have you tried disconnecting the battery for a few minutes to let the electronics reset? and are you sure there's no vacuum leaks anywhere?

 

Yea I had the battery disconnected for about 10 minutes after it and sprayed carb cleaner on intake hoses while it was running looks like there’s none.

 

well my "expertise" pretty much only applies to 1998 - 2000 model years lol so i'll let someone else take it from here... best of luck getting this resolved! my only other instinct would be to think ECU capacitors since that's an increasingly common issue on early LS years

 

i second the ECU caps and suspect a vacuum leak. consider doing a smoke test thru the intake.