Grey2006GS

Hello all,
Having owned (still own it) a 2006 GS430 for 5 years and 70k miles (the car has 310k), I thought I'd venture into another 8 cyl Lexus. My 430 has been so smooth and impressive even after 310K that I thought all GS's would be similar to it. Anyway, I just acquired a '99 GS400 with 120k on the clock. I must give credit to the car's prior owners for taking such great care of the car. It's condition is nothing short of spectacular for a 25 year old car.

Anyway, I am running into a few issues with the car's acceleration and braking that I can't seem to figure out. I've googled and youtubed everything I can find on my issues but still can't seem to find the answers. I am hoping the experts here are able to steer me in the right direction.
1. When starting from a stop, the initial ease onto the gas peddle will get the car going for a split second and then the rpm will drop, as if in limp mode unless I continue to give it gas at a somewhat aggressive rate. It feels as if there is a dead spot of 0.5 inch after the initial depression. To bypass the dead spot, I would have to continue to give it gas. Normally, this wouldn't be a problem if I were to travel on open roads with no other cars. But, the bay area doesn't allow you that luxury. Also, it gets dangerous because I have no idea when the car will take off and when it will be in limp mode. I've had a few instances where easing into the gas peddle lunged the car forward as if I were in a drag race. This is a fast car, faster than my GS430. Prior to my acquisition, the dealer claimed to have replaced the ECM and throttle body with used units. Not sure if I should send my ECM to SAI for a rebuild. I have not cleaned the throttle body yet, but I plan on doing that shortly. My 430 doesn't drive this way.
2. When cruising, the rpm will sometimes drop for no reason at all. I've never experienced this with any of my other cars, present or past. Don't know if this is normal. I do have multiple Lexuses in the family and nothing drives like this. Hoping someone can tell me if all of this is normal or not. I did have a Lexus tech look at it and he mentioned during his test drive that he experienced one episode of an rpm drop and that to figure out the problem, he would have to start replacing parts, process of elimination. I am hoping we can avoid that.
3. Brake pedal sticks a bit. When released, the pedal will not immediately bounce back. It sticks for a split second before it springs back. I've read some people were able to find success to this problem by bleeding the brakes. I am planning on bleeding the brakes also.

I am hoping you experts are familiar with my issues and are able to give me some advice.

thanks in advance.

dwoods801

Your not getting any CEL? Do you have a scanner? See if you can find what the Throttle blade percentage is? Some cars can be as low as 70%, if ita had throttle body replaced, it could need some adjustment. You want to get up in the 90% range. Seems like most performance issues are going to gemerate a CEL, if its not, then that alone ahould narrow your possible culprits. I would try to identify tue problem before you start replacing parts or trying random stuff. Sometimes that can make it mote difficult to resolve.

Grey2006GS

Thanks for the reply, dwoods801. I wanted to post that I may have solved the problem this afternoon and then I see your reply. I think it may have been my throttle cable, too much slack. I tightened up the cable and it seems to drive fine now. Drove it around the block a few times, and so far so good. I'll take it to work tomorrow for confirmation.

dwoods801

These cars are all drive by wire, and use a throttle pedal position sensor and then it feeds an electric signil to an electric motor on the throttle body, there is a cable that partially holds the throttle but its more of a backup that is just to help you get the car home if there was a problem with the DBW system. I believe that cable is what controls the transmission downshift, when you floor it. If it's great now, then that's great, if you find it still isn't accelerating in a smooth and linear motion, just update this post, and we can cover some diagnostic tests. 👍

DMPesso

I also have a GS400 and when I tightened the throttle cable it felt like a new car. Made it so responsive. Definitely helps a lot and takes away any slack in the pedal. I’m surprised to hear you say the GS400 is faster, I would figure the 430 would be since there’s no gears and it’s newer.

cleaning the MAF also helped a lot. Considering the car is 25 years old it wouldn’t hurt to replace it. I noticed a difference in performance as well after replacing it.

Grey2006GS

interestingly, my CEL came on Monday night with P0763, shift solenoid c. I made the cable adjustment Sunday afternoon. Not sure what to make of it. Do you think it has something to do with the adjustment of cable?

Grey2006GS

honestly, I’ve only put 1k miles on the 400 so far. From what I experienced, during a downshift, the 400 is more instantaneous than the 430. Maybe it’s bc my 430 has 310k on the clock and the 400 has 122k. Not sure.

I tried a new MAF sensor and it immediately threw a CEL. Since my old unit was fine without a CEL, I swapped it back with the old unit. Tightening the cable has made it much more enjoyable to drive, especially in a slow traffic environment. Before the tightening, it would take me a while to ease into the gas pedal without causing it to lunge forward. Scary sometimes.

Grey2006GS

just an update: So I started the car this morning and I still see the CEL. I proceeded to remove the washers I used to tightened the cable and the CEL light went off. So, I played around with it and re-placed the washers again and drove it around for 30 min and light still off. Not sure if it's just a coincidence or a bad intermitten solenoid, but I'm just going to drive it around and will update over the next few days. Fingers crossed.

DMPesso

I think I had that code in the past and it was a solenoid on the transmission but I got it to go away by doing a few drain and fills on the trans.

a new MAF shouldn’t throw a code, did you get one of those “oem” ones from eBay or was it actually from the dealer? I got mine at discountpartsmonster. They seem to have the best prices on oem parts.

DMPesso

It’s the throttle cable that helps the response. I had a 2001 GS430 before my 99 GS400 and the difference in throttle response is night and day, especially after tightening that throttle cable. I hated the lag on the pedal from the electronic throttle on the GS430! That was the main reason I sold it.

I also turn off vsc, especially in traffic. Helps keep the car in a lower gear. Also I use the e shift. Keep it on 4 and it has no hesitation even in traffic

Grey2006GS

I got it from Amazon, definitely not OEM. Will for sure remember discountpartsmonster and to use only OEM. Thank you

Grey2006GS

Thank you for the insight. I picked up this car because I was so impressed with my ‘06 430, no hesitation or lag. I’ve had an M5 and an E55 as a dd before, but the smoothness of the 430 won me over. I have to say I was a bit disappointed with the 400 before the adjustment, but now that it has been adjusted, it’s been a different car. Definitely growing on me.

DMPesso

yea that’s why it threw a code. It has to be OEM on this car. For the $150 or whatever it was it’s definitely worth the upgrade. The sensor inside is over 25 years old. Definitely not going to perform like new.

Yea just wait until you replace everything that needs to be replaced. Spark plugs and o2 sensors make a world of a difference as well in the performance and response on the pedal. My GS400 drives better than new cars because I damn near replaced everything.

the only downfall of the 2GS is the infamous shakes at 65 mph and the horrible suspension design. Other than that, it is over engineered. I wish it had the LS400 suspension. It would’ve been the perfect car

Grey2006GS

What "shakes" are you referring to? I was thinking as soon as I have the necessary maintenance issues taken care of, I will start looking into upgrading the suspension. Comparing the '99 to the '06, the '06 rides a lot better, not as floaty. What do you recommend for the '99? Not looking for a track setup but something a bit more firm.

DMPesso

most 2GS have the infamous shimmy in the steering wheel at 65mph.

honestly I kept it oem because I love the smooth ride but if you want to change the struts try kyb or possibly Sachs. Lexus chose to use Sachs for the Lexus GSF so they might be worth looking in to. I changed all the control arms and the suspension with oem. Makes a huge difference in ride quality especially out here in NYC