Posted 20 April 2012 - 12:13 PM
I hope you haven't done this already!!!
The AHC is what makes an LX470 what it is. I had the same issue on my 2002 LX470 with over 230K miles. Mind you, I bought it 8 years ago with 32K miles, so as you can see, this car has been through a lot.
That being said, I was having the same issue with my car for the past 2 years, where the front of the car was all the way at the bottom, and it felt like I would go air borne if I drove on a rough road. I went to the dealer and got the exact same answer, "It'll be $280 for diagnosis, we might have to replace the AHC system to find out if that's the issue, cost will be over four grand...yada yada yada."
Anyway, I did months and months of research. During this, I changed the Suspension oil ($50 from the dealer, do not use any other oil) - No results. Then I figured, I'd bite the bullet and change both of the "Front Height Control Accumulators". I teamed up with a mechanic, and he bought them for me (at his price) from the Lexus dealer closeby for a little over $500 a piece. I took the car to him to get them replaced, thinking it'd be an all day job. Turns out, it took him one hour. It's a simple unscrewing-screwing back job underneath the car, and bleeding the suspension fluid so no air is trapped in them (usually this would have resolved the issue if your Accumulators are bad), but I got no results. I could feel the sweat dripping down my spine now. I had just dished over $1,000 for something that wasn't even the issue.
So the mechanic looked around some more. My mistake was that I didn't get it diagnosed by him before I asked him to order the Accumulators for me. What was the find after 10 minutes of looking around?
The front passenger side "Height Control Sensor" was in pieces and needed to be replaced. So he called up the dealer again and I picked it up for another $300+. After installing this, the mighty LX470 car rose it's head as it used to, when I met him the first time.
MORAL OF THE STORY:
GET IT DIAGNOSED THOUROUGHLY BY A TRUSTWORTHY MECHANIC BEFORE DOING ANYTHING.
Total cost was a little less than $1,800 including labor (which could have been around $500). But I don't regret it a bit because it's been two months now, and I have driven the car for over 4,000 miles, and it rides 'in the air' the same way as it was riding the day I bought it.
A WORD OF CAUTION and/or ADVICE:
PLEASE HAVE YOUR SUSPENSION FLUID CHANGED AT EVERY 60,000 MILES TO MAKE THE AHC SYSTEM LAST FOREVER. I was never told this until I ruined it (or may be not).