Nose drops at speed AHC 1999 LX 470

[4FLATS]

I think I have a problem with my AHC, As long as I have owned this thing (7 years or so) the nose drops at speeds over say 45 mph, just about 1" and when you come to a stop or drive under 20mph for a while it comes back up.

I always thought this was for gas MPG. Now folks are saying this is not standard. Anyone else have this happen?

 

[PADDO]

Is the front lowering or the rear raising? Random behavior or repeatable and predictable? How do you know it drops an inch or does it just feel different at speed?
There is nothing in Toyota/Lexus literature that describes just the front lowering aka RR highway mode (and even then RRs lower all the way around). I could see the rear raising an inch if the rear sensor is failing or loose, but that would more than likely be a random event until it just broke and you were either on the bump stops or stink bugged.
I guess the best place to start is whats the general health of your AHC? last fluid change and bleed, front and rear vehicle heights at rest and neutral pressures? Does it raise and lower on command and approximately what's the cycle times for raising and lowering? Any DTCs etc?
Hooking up techstream to monitor the leveling valves and height sensor feedbacks whilst driving is the best way to see what's happening.

 

[uHu]

It is normal that the front, and rear, adjusts according to the situation. AHC is Automatic Height Control - i.e. it adjusts the gas-spring pressure to maintain a set standard height. But it does it in intervals - let's it get half an inch up or down and then adjusts at least that much. So, after driving, it is normal that it settles to normal height after stopping. And, when going uphill, or at high speed, the nose will lift a bit, which the AHC compensates for by lowering the nose again.
If it always adjusts to the right height you are probably OK, but do check the sensor linkage, they do wear out, or work themselves loose, in which case the AHC ECU wouldn't know exactly where it is, so to say. Normally, if a sensor is malfunctioning, one end goes all the way up, or down.

 

[H E A V Y M E T A L]

just remove it. I am. When I bought my LC I started trouble shooting the AHC for a second... then I realized one reapir job to that unit and it covers the cost for a nice lift kit. and if you do repair it, you just have the same system to look after again. I'll pass on that. I have the maual and it makes finding and disconecting really easy. AHC; Great idea for pavment machines only- I bought mine to destroy one trail at a time muuhahahahaha.

 

[jLB]

I think I have a problem with my AHC, As long as I have owned this thing (7 years or so) the nose drops at speeds over say 45 mph, just about 1" and when you come to a stop or drive under 20mph for a while it comes back up.

I always thought this was for gas MPG. Now folks are saying this is not standard. Anyone else have this happen?

The 1990 LS400 that I used to have would to drop to "low" at higher speeds (as it was supposed to), but I've never noticed our LX adjusting AHC (from N) at speed.

 

[jcrandall]

Before I took it out, my AHC dropped the nose at speed. I'm not sure how much it dropped, but it felt like a hell of a lot more than 1". After like the 4th or 5th time, I had to take it out.
Extremely disconcerting and one more reason to take it out when it's time. When it's working, it's pretty damn cool. When it's not, dangerous imho.