kroz

I just purchased a 99'GS 400 (love it) I find it to lag at stop lights though. I have read that this is just a flaw with the vehicle. Can resetting the ECU help this problem? Or should I just leave it alone. I have read alot of discussions about the problem but cannot make a decision on the matter. If resetting is the answer then which is the correct method.

gserep1

Hello,
Could you be a little more specific on the "lag" problem? When does it lag? Is it at "tip-in" or just off idle, or is after it takes off, and then does a slight bog while going through the gears?

I know that the newer GS-430 have a "hesitation" just at take off. This is due to the throttle plate being controlled by a motor. It is all electric / electronic, and is just the nature of that beast. The older 400's have a cable arrangement, and I can tell you that I have no lag at take off.

I have 79,000 miles on my 99 GS-400, and it is VERY quick all the way up. It is definitely fast enough for me.

Mine idles at 500 rpm in drive without A/C, and about 750 in drive with A/C on. It has always been smooth.

Hope to hear from you soon!

GSEREP1

DaveGS4

iTrader: (2)

Kroz,

Resetting your ECU should help, try it it's free. BUT you have to do it from time to time (not a permanent fix).

Either way of resetting you've read on our forum will work (disconnect positive lead from battery or pulling ECU fuse) equally well.

alsilverbullet

I thought we had to disconnect the negative lead or remove the ecu fuse.

Letsride

Yes this is the prefered method.

Kroz we need more info on the car ie: Mileage, last service etc...

bmgs400

I have a 99 GS4 that hesitates from a dead-stop takeoff. It's like the throttle response or tranny is lagging. Try it with the VSC-off and ECT-pwr, I can feel the improvement.

SeattleGS400

iTrader: (1)

My notes on hesitation (on my '99 GS400):

1. From a standstill: no hesitation is apparent. I mash the gas, and zoom it goes.

2. From a roll (i.e. at a constant speed): hesitation is apparent. I mash the gas, at say 20 mph, it seems the car's computer thinks/pauses for about 0.3 seconds, then it finally does it heave-ho and zooms. It's not quite the best thing, as those 0.3 seconds could mean an accident. . . However, if I just say apply about 25% throttle, it seems to respond to that just fine. . .

I don't know if it's a Lexus ECU program leaning towards a more cush/luxurious ride over engine performance issue?

SeattleGS400

iTrader: (1)

Another thought on the hesitation. I wonder if it's caused by the car needing to downshift first? From a standstill, it starts in 1st, give it WOT, and it just goes. From a rolling start, say at 20 mph, it seems like the 0.3 second lag is caused by the car needing to downshift first. As most of us know, the car automatically upshifts rather early (probably to save on gas), so from a rolling start, it might be in one gear too high, so it has to downshift first, then applies the gas when we give it WOT. Most normal car automatics require a bit of time to downshift (not as fast as human professional race car driver shifts, unless you're talking about rather exotic SMG automatics), so it could the source of the hesitation.

Something to try to verify all of this--manually put the car in a gear using the shifter gate (i.e. NOT using the E-shift), and roll at a certain speed, then hit the gas. It might be something to try and see if the apparent hesitation occurs. Say speed to 25 mph in 2nd gear (using the gate shifter), then give it WOT (or drive to 45mph in 3rd gear then giving it WOT). If the car does not hesitate in the locked gears, then we can safely say that the lag is probably due to the car need to downshift first before applying gas to the engine.

bmgs400

Hey SeattleGS400 I think your right-on-the-money with your analysis. Indeed the downshifting takes time when driving with the tranny in "D". Mine will downshift to 3rd from 5th when giving it WOT from a rolling start (20~40MPH) and the rpm's are too high when it finally kicks in. To make it smoother I just drive in 4th most of the time and 5th only for the highway.

From a stop though, my car seems to lag slightly then vrrrrroooom!!! I don't like the lag (even with VSC off and ECT-pwr). I have stock wheels and so-so all-weather tires, and I can't spin the tires from a dead stop takeoff. I want to leave some rubber...

SeattleGS400

iTrader: (1)

bmgs--you know, your comment of 5->3 downshift reminded me of something. During a normal cruise around town, the car will upshift to 5th gear at around 30 mph (since it has lots of torque). Push the gas, and it has to downshift to 2nd gear before zooming away--that has to be the reason of the apparent hesitation during rolling starts on WOT.

kroz

I can not tell all of you how much I appreciate the immediate responses. Here is what I know about the car year 99/milage-76k-very very clean. Last service unknown? According to the dealer an elder gentlemen owned the car and traded it for a new 350z. That sort of tells me he had an eye for speedy cars. From what everone is saying I guess I can best describe this hesitation being from a dead stop, say paying a toll. But you guys hit it directly on the head give it gas and off it goes w/o any problem it actually makes me nervous.

PHML

iTrader: (33)

Maybe its a sticky throttle body....you should check it out...it may need to be cleaned.

Pete

bmgs400

Kroz - You and I may have similar problems. I bought mine with 86k miles in July. Up to 104k now.
PHML - What needs to be disassembled to check/clean throttle body?

I have a lag problem too, so I ran a few dead-stop takeoffs last night paying attention to the tachometer. My acceleration is sync'd with the tach, so the takeoff lag is a response to engine lagging....not the tranny since it starts in 1st gear anyway.

What could cause this lag? Throttle body sticky, Mass air flow sensor dirty, air filter dirty, weak gas, ECU learning bad habits...damn computers.

I do use 89 octane...could this lead to problems? Should we be using 93+ octane? Doesn't say in the owners manual.

What do you put in your gas tank?

PHML

iTrader: (33)

Dex posted a DIY on his website. Here's the link:

http://www.digitalsimple.com/The%20G...rottleBody.htm

I use 92 Octane Premium gas. I would suggest to clean the air filter, flush the trans fluid, replace engine oil w/ Mobil 1 SuperSynth (if not already done), and then reset the ECU.

Good luck.

Pete

PHML

iTrader: (33)

I don't do this but I know a few ppl who swear by it.....MOTH ***** (must contain Naphthalene) to boost octane in your gas tank.

Pete

-------------------------------------

Moth *****

Moth ***** can be used to increase the octane rating of the gasoline your are using. The higher octane not only increases power, but will also increase gas mileage. The ratio is 5 moth ***** for every 1 gallon of gasoline. Place moth ***** in gas tank before fueling the car. Also add 1ounce of WD40 per gallon of gasoline. This will help remove water from the gasoline and make it ignite better.

( Note: The moth ***** must contain naphthalene.)