I noticed something similar - a slight hesitation/lunging after acceleration when the car is cold between 2nd and 3rd.

When I asked a service rep. at my dealer about this he said this was due to the catalytic converter "not being warmed up."

I went to "How Stuff Works" to improve my knowledge of catalytic converters:

http://www.howstuffworks.com/catalytic-converter.htm

The article mentions the catalytic converter needs to be hot to work properly but it doesn't explain why a cold catalytic converter would cause a hesitation or vibration.

So, if by design as noted by bitkahuna, the engine control unit is actually causing the hesitation/vibration by ?????

My guess: by varying the air to fuel ratio between 2nd and 3rd to allow the cat. converter to warm up to peak efficiency and limit harmful emissions. Different air to fuel ratios would provide different levels of power hence the vibration.

Can anyone confirm or repudiate this?

This leads to more questions: Why between 2nd and 3rd? Why between shifts at all?

All these questions! My head hurts. I'm just going to drive my car and ask questions later!

 

1) The OEM tires, RE030, will track on any groove on the road no matter how smooth the road is. I have had some very bad experiences from these tires. Vibration, noise, hydroplane, etc. So, I switched to Yokohama AVS dB and problems solved.

2) Well, on my car the exhaust tip on the passenger side is 1 inch lower than that on the driver side. One way to fix this is to change the rubber hangers. Otherwise, see what the dealer can do about it

 

how do you like those AVSdb's? any peeve?

 

MGS4, you are right it may very well be the tires, but since they are brand new, I'll use to them up first.

As for the exhaust tip you can scroll back to see my other thread when the dealer is ordering a center piece to fix this problem. At least they are doing something about this. Good luck!

 

OK here goes... on mild acceleration, any automatic transmission will normally shift up at low rpm, resulting in a gentle shift. Normally automatic transmissions never let the rpms climb quite high (3K maybe) on gentle acceleration, because a) there's no need, and b) it is inevitably going to result in a harsh shift. But the Lexus transmission does this, ONLY when the engine is stone cold, to warm the enginer and cat converter to reduce emissions more quickly.

The reason it occurs between 2nd and 3rd is that the car doesn't even bother with first gear accept on full throttle starts, and holding rpms higher in 1st on gentle acceleration would probably result in an even more harsh shift than from 2nd to 3rd.

As far as a hesitation, the trans is just trying to do its best to shift as smoothly as possible, and I don't know about any vibration, except for the fact that the rpms are higher than they would be once the engine is warmed up. I don't notice it on the V8 - maybe it's more noticeable on the inline 8, which is inherently less smooth.

I hope this helps.

 

Actually, the inline 6 configuration is smoother than a V8.

 

I guess I was thinking of V6 vs V8. Either way, in driving both the GS300 and GS400, the 400 feels smoother to me particularly at higher RPM.

 

You guys are truly the experts and that is why I enjoy this website and forum so much.

All I need now is to fix my uneven tail pipes. Check out my latest gripe in the thread, that reads PARANOID - Leaving my GS in other people's hands.

Thanks again for all your comments and input!

 

Update on this issue and thanks again to you all for all your help and comments.

The Steering is now much better and a little tighter too, since the balancing of all 4 tires. So no more vibration in the steering wheel for now (Knock on wood).

The part for the fix (Center Pipe) for the uneven tail pipes has come in and I have service next week to install it, so we'll see how that works out. This is more of a cosmetic issue and it just looks bad from a quality standpoint, since it passed Lexus Inspection.

Will keep you updated.

 

Hi,

I am noticing the same thing with the uneven tailpipe on my 430, and I am wondering what the fix is? the part name, and what should I ask when I bring it to the dealer? Is it a warranty work?

thanks,

 

Lex430,

All they could tell me is that they ordered a center pipe piece to fix this problem. I'm going next week to have it done and will ask, but it's all covered under warranty, so if it's bothering you like it did for me, then call and schedule. They should be able to take care of it for you. Other members here talked about something to do with the hangers.

The uneven tail pipe issue is just a hassle for me. Never should have happenned!