SC400MAN

iTrader: (1)

I work at a Lexus dealer and we just got in an IS250 with the 6 speed manual. I have driven it and was disappointed with the way it shifts - more particularly the way the engine speed does not drop as you push in the clutch and let up on the gas. It seems to stay 500 rpms too high to allow for a nice smooth shift. I have a Supra with a 5 speed, so I am used to driving with a clutch. It just seems impossible to shift smoothly. I asked our head tech and he was not sure of what the problem might be. This is only the 3rd manual we have had.

Any suggestions from the IS community?

Thanks

The Chad

I have driven several manual transmission cars in which when your engage the clutch, the RPMs do not fall off immediately, including the S2000 I own. It seems to only ever really occur when the vehicle is warming up, and the ECU idles the engine at almost 2k instead of the 1k it normally idles at.

Also, the engine freely revs and when you engage the clutch, perhaps intertia or whatever (less resistance), is not slowing the engine speed as quick as what you are accustemed to. I have no idea on this, however.

ff_

I've posted comments on this very thing several times before, and got zero response. Yes, this is a big problem with the manual-equipped cars. When you have to wait 2 seconds between shifts to let the clutch back out, this makes for a very un-natural experience when rowing through the gears. It also keeps me from truly enjoying the car. And with the short first gear in this car, combined with the rev hang, I get people quite nearly rear ending me when taking off from stoplights. Accelerate... push clutch in...wait...wait...wait.... guy behind me is now right on my rear bumper...shift into 2nd...wait...wait...let clutch out...guy that was behind me has gone around, and is now 10 car lengths ahead of me.

I'm pretty sure that this behavior is due to emissions controls features. When you quickly "snap off" the gas (i.e. like when you're shifting gears), that causes extra gas to go through the combustion process without being burned, resulting in more emissions. The way carmakers have been solving that is to artificially hold the revs, and then slowly let them drop. It's annoying as hell. And it's much worse in the Lexus than any car I've ever driven.

Well, evidently Honda and BMW (and others?) have found a way to let the revs drop freely without sacrificing low-emissions status. If you drive the S2000 or any current model BMW, the revs drop between shifts so quickly that you can pretty much shift as fast as you want to. In fact, to properly match revs for the new gear, you either have to shift very quickly, or hold the revs yourself. This is how it should be.

Anyhow, like I mentioned, this feature of the car is keeping me from enjoying being behind the wheel, and I've been having frequent thoughts of selling it, and buying a 325i. If there's a channel that we can go through to let the Toyota engineers know what about this problem, I'm all for it.

When I get a chance, I'm going to pull the plastic covers off the engine and do some peeking around. It's entirely possible that the revs are held mechanically, and something can be modified. However, I expect that it's probably something in the OBC that is programmed from the factory.

ihkskim

or maybe we can get a lighter flywheel

clubfoot

ff you've hit the nail on the head, emissions is the culprit and Toyota have not found a way around it ,...yet. A lightened flywheel may reduce it but it will still be there.

SC400MAN

iTrader: (1)

Thanks for the info. We had thought it might be related to emissions. If anyone has any suggestions on a cure, I will appreciate the information. It is a little hard to sell the car when the test drive is not smooth!

ff_

I went for a drive last evening, and discovered some more things. When the engine is cold, the engine has a much lower tendency to hold revs between shifts. Once up to normal operating temperature, it becomes simply awful. From an emmissions standpoint this doesn't make much sense. If anything, the potential for unburned fuel being dumped through combustion process when snaping the accelerator off is going be nuch higher when the engine isn't up to normal operating temps.

But in any case, since the behavior is noticeably different between when the engine is cold, and when it's hot, then I'm going to assume that this is controlled electronically. Which is a bummer. Still, I'm going to dig under the hood and see what I can discover. I'll post my findings here.

SC400MAN, if you work for a Lexus dealership, maybe you know someone in the shop that can comment? They're going to know a lot more about the car's emissions controls than I will.

miguel

Hey
I'm new to these forums this is my first post. I bought a IS 250 6spd sport pk and glacier frorst white in colour. My opinion to this topic is ; I used drive a gti vr6 and drag race it alot at the strip. I once installed a lightenned and balanced fly wheel and it made a hell of a difference the car reved so much faster like an F1 car but the revs also dropped alot faster. Supposedly the set backs are increased vibration in the cabin( I never noticed any). To my opinion Lexus most defenitely installed a big heavy flywheel for a smooth ride and that's why the revs dont drop. It also makes sense on the guy with the honda S2000 why would Honda want the revs to drop if the car revs up to 9000 rpm and starts making power at 6000 rpm.

SC400MAN

iTrader: (1)

I have discussed this with our top mechanic and because we have not had many manuals and no complaints, he didn't have time to check into the issue. That's why I asked here - thinking I could go back to him with some specifics and get him to check with Lexus Technical. I will keep you updated.

Wid IS350

Certain Honda (or the Acura TL 6 speed, at a minimum), drop the revs between shifts only to a point where it will make for the smoothest shift into the next higher gear. So if you tach it out in 1st, the rpms will only drop to around 3k for your shift into 2nd based on the cars computing.

Maybe it's the same for the Lexus 6 speed?

4TehNguyen

iTrader: (1)

manual makes 3-4 less mpg than the automatic, heard its not geared optimally as the auto is

Pittdawg

Ya but atleast it makes the 250 driveable, the 250 with an auto I drove was such an absolute slug, with a manual it feels much more "peppy".

4TehNguyen

iTrader: (1)

yea the 250 auto is pretty sluggish but I had a different solution for that

ff_

The purpose of the flywheel is to store momentum, reduce vibration, and smooth out the loads transmitted to the drive train. If the problem with the 250 was simply a heavy flywheel, then it would be slow to drop revs all the time. However, as I posted earlier, there is a very noticeable difference in how quickly the revs drop when you compare shifting when cold, and when fully up to operating temps.

The reason why you want revs to drop quickly is because the faster they drop, the sooner you can shift into the next gear and let the clutch back out. When you have to wait 1-2 seconds between shifts, that's a lot of time spent coasting, when you should be accelerating.

And the other guy you're referring to with the S2000, his car must be very different than the S2000 I owned. The revs on mine would drop very quickly, and this is how it should be for the best performance. Well, you could say "farq it", and just shift and let the clutch out early every time, but you'll be replacing your clutch set in about 15K miles.

Oh, and to clear something up, the S2000 doesn't start making power at 6000 RPM. People that say things like that have obviously never driven one.

9520G

Yeah, I have the manual trans also and I have the same problem, also that grinding noise in first and second gear. Even the people from car and driver noticed it. My best solution to date even though not the smartest is to ride out the clutch a little bit and it definitley smoothens evertything out!