Toyota FJ Cruiser Forum banner

The Auto-Tranny FJ "Lunge"

43K views 147 replies 105 participants last post by  Robot 
#1 ·
We have all been there. Sitting at a stop light. All of a sudden you feel this "bump" from the rear. Almost feels like a light tap from the car behind you. Of course they are so freaking close you can't see them anyway, but I digress... :)

I still have no idea why the AT FJ seems to lunge, but I do have a theory. Here are the facts:

It only happens when the A/C unit is on. That means in A/C or Defrost mode. The ScanGaugeII reports position "15" when reading TPS (Throttle Positioning Sensor) and when the "lunge" happens the TPS reads "16." A very common occurence with vehicles with A/C. The idle pops up a bit when the compressor turns on. However, I have never had a vehicle before that "lunged" like the FJ does.

As for the "lunge" here is my theory. Since this AT has a variable torque converter I suspect that has somehting to do with it.

Does this happen with other Toys that have this same tranny?

Anyway...for what it's worth, that's what I have noticed with my FJ.
 
#2 ·
It seems that when the compressor cycles it does that and yes I have had this happen on other Toyota's. I guess I am just used to them doing it because I don't even notice it and the FJ is my 3rd Toyota.
 
#3 ·
Haven't felt the bump or lunge yet, only have 170 miles on my FJ.
 
#11 ·
You will. It just feels weird. You truck isn't going to actually move, but it kinda feels like it. It doesn't actually "lunge" forward, but that's how people have referred to it.

I haven't run the A/C compressor but, I am in panel/defrost mode with heat.
When you run the defrost mode, the A/C pump runs. So, one in the same really.

Feels strange does it not.....its like the tranny is spoolin up...MR Willy does it also when cold
Also, I noticed it only does it once per stop. So yeah, almost like it's spooled up and once spooled, it's happy. Until the next stop.

Anyway, it's nothing dangerous. You FJ is not going to slam into the car in front of you, but it sure is a bit disconcerting when you first feel it.
 
#6 ·
Mine does the lunge. Not really a problem but when I read the thread title, I immediately knew what you meant. Yea, it's almost like getting tapped in the rear end but too soft.

I haven't run the A/C compressor but, I am in panel/defrost mode with heat.

I have guessed it must be the torque converter or something like that.
 
#7 ·
Ive had it happen in my 99 4-runner, and the FJ, its slight, if you press the the break peddle with more force then a feather it is a non-issue.
 
#12 ·
Would it not be the IAC letting more post-MAF air bypass the throttle body to compensate for the increased drag in order to maintain consistent idle?

Mine also does it when stopped and turning the steering wheel, seems like the same thing, ECM/PCM/ECU whatever, compensating for a drop in revs.
 
#15 ·
I have felt the "lunge". Not sure if AC/Defrost is on at the time of occurance. I make it a habit to leave space between the car in front and the FJ. I owned an 2000 Passat and it "lunged" forward in park. This took some time to get use to, you stop the car put in park and all of sudden it lunges forward. I guess this was normal as well.
 
#41 ·
I have to agree on this one, lol. Yes mine does it too. I always whip my head back hoping noone bumped me......and there is noone there. "I see dead people."
 
#17 ·
I had an opportunity to drive an FJ at the Auto Show in Orlando Fl. back in November. Toyota built an off-road challenge course in the parking lot. One of the obstacles was a "teeter-totter" where you as the driver had to drive up a ramp with a center pivot and then proceed down when the ramp transitioned. Having already had my FJ for a week or so, I thought it would be cool to try and balance the FJ on the center. Sure enough... the a/c was on and with very light braking trying to find the center of gravity... the compressor kicked in and sent me and the ride-along guy down the other side. He wondered what happened, I replied... FJ's don't like to wait around doing silly things, they like to go!:roller:
 
#18 ·
I have had my FJ for almost a whole year now (March 31st) and it has been "lunging" for quite some time. It does it at least a few times every time I drive it. Since I live in Florida, I have not used the A/C for the past several months, and it still lunges. I have gotten used to it by now, even though it can be somewhat disconcerting and annoying at times. It definetly bothers my wife more than it bothers me!
 
#19 ·
We have all been there. Sitting at a stop light. All of a sudden you feel this "bump" from the rear. Almost feels like a light tap from the car behind you. Of course they are so freaking close you can't see them anyway, but I digress... :)
Dude... I just said that in another post :D Mine has been like that from day one (Jun '06) but didn't think too much about it.

I do the same.. A lot of cops around my kids school, so blocks away from the school zone I am already in 4th or 3rd (manually) just to make sure my lead foot doesn't get carried away.

EDIT: only really weird thing that I have noticed was if I am stopping fast at a light, once stopped the trans (slightly, but suprised me the first time) jumps into 1st..
 
#20 ·
Dude, I know that. It has been yakked about for a long time. ;) Just now that we have access to the computer via a ScanGauge, we can now actually "see" what it's doing.
 
#22 ·
lol, my inability to keep up with 10mil threads is showing..
Don't even try! :) We're on a whole different tangent here. The ScanGauge reveals a lot about what your FJ is doing.
 
#23 ·
And now back to our regularly scheduled program...

So...now does anyone know why the tranny does that? Is it the variable torque converter?
 
#24 ·
This is a common problem on all automatic transmission 4wd Toyotas. The driveshaft slipyokes bind due to lack of lubrication.

When you come to a stop the powertrain shifts forward on the rubber engine/trans mounts. The slipyokes have enough friction in the splines of the slipyokes, coupled with the tourque of the engine preloading them even tighter, that the powertrain is temporarily held in the "shifted forward" position. When you slightly release the brakes the tourque applied to the driveline is reduced enough to allow the slipyokes to release and let the powertrain to relax back to a neutral position on its rubber mounts.

Toyota has come up with several somewhat ineffective fixes. The only thing that really works is to completely lubricate the driveshaft slipyokes. Slowly pump grease into the zerk fitting next to the slipyoke until it starts to ooze out of the slip yoke. Too much pressure will blow the cap out of the slip yoke, preventing you from ever being able to properly lubricate it. Be sure to do both driveshafts. It will throw some grease off the first few times you drive it so you might see some smoke from where it lands on the exhaust.

As far as I know, manual transmission vehicles won't have this problem because there is no torque applied to the driveshafts whan you are at a stop.
 
#36 ·
This is a common problem on all automatic transmission 4wd Toyotas. The driveshaft slipyokes bind due to lack of lubrication.

When you come to a stop the powertrain shifts forward on the rubber engine/trans mounts. The slipyokes have enough friction in the splines of the slipyokes, coupled with the tourque of the engine preloading them even tighter, that the powertrain is temporarily held in the "shifted forward" position. When you slightly release the brakes the tourque applied to the driveline is reduced enough to allow the slipyokes to release and let the powertrain to relax back to a neutral position on its rubber mounts.

Toyota has come up with several somewhat ineffective fixes. The only thing that really works is to completely lubricate the driveshaft slipyokes. Slowly pump grease into the zerk fitting next to the slipyoke until it starts to ooze out of the slip yoke. Too much pressure will blow the cap out of the slip yoke, preventing you from ever being able to properly lubricate it. Be sure to do both driveshafts. It will throw some grease off the first few times you drive it so you might see some smoke from where it lands on the exhaust.

As far as I know, manual transmission vehicles won't have this problem because there is no torque applied to the driveshafts whan you are at a stop.


I also have this "lunge condition" thought it had something to do with the drive line,, and not the a/c,, anyway the a/c is more of a surge from my experience,,
so on my second oil change I greased everything underneath,
and sure nuff,, that lunge is non-existant on normal stopping,, but it is still there on hard stops,, but not as bad..
I'm going to use this lunge thing as an indicator for driveline maintenance..
 
#29 ·
Excellent Post...Thank You...thought I was on drugs, I kept thinking someone tapped me in the a@@ ( no... not that you preverts...I know it's "pervert")
when I stopped...Look in mirror...oh...I mean blind spot...no one there...huhmmm...maybe behind the spare? Nope not there either...that was strange...anyway. Thanks for esplanen' Ricky.

This is a common problem on all automatic transmission 4wd Toyotas. The driveshaft slipyokes bind due to lack of lubrication.

When you come to a stop the powertrain shifts forward on the rubber engine/trans mounts. The slipyokes have enough friction in the splines of the slipyokes, coupled with the tourque of the engine preloading them even tighter, that the powertrain is temporarily held in the "shifted forward" position. When you slightly release the brakes the tourque applied to the driveline is reduced enough to allow the slipyokes to release and let the powertrain to relax back to a neutral position on its rubber mounts.

Toyota has come up with several somewhat ineffective fixes. The only thing that really works is to completely lubricate the driveshaft slipyokes. Slowly pump grease into the zerk fitting next to the slipyoke until it starts to ooze out of the slip yoke. Too much pressure will blow the cap out of the slip yoke, preventing you from ever being able to properly lubricate it. Be sure to do both driveshafts. It will throw some grease off the first few times you drive it so you might see some smoke from where it lands on the exhaust.

As far as I know, manual transmission vehicles won't have this problem because there is no torque applied to the driveshafts whan you are at a stop.
Ahhhhhhhhh...the ol' zerk fitting and slipyoke theory...makes perfect sense know! Do I need to worry? I can live with it...you know the feeling of being tapped in the A@@...but only with A/C on...:alfdance:
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top