During coasting, (foot off the gas paddle) from 40-60 mph the RPMs stabilizes at 1100RPMs then feels like the car down shifts and RPMs rises 200-250 RPMs. The car is still in the same gear. This happens two to three times before actually down shifting to a lower gear. Has anyone noticed this? Is it normal?
This is happening in fourth ands fifth gears. I'm think about taking it to the dealer.
Q

Same behavior here. Almost seems like its bouncing off a low rev limiter.

Just be happy it's running :puzzled:

:trophy:

This post has been edited by andyman32: May 7 2008, 05:45 AM

Do you have a check engine light on yet? My car did that and it went away when I replaced the speed sensors... The input caused those problems for me... The output controls the upshift, the input controls the downshift and the vehicle speed sensor controls a little of the upshift and downshift and if its bad will also buck into 3rd gear on the freeway.

The only thing I could think off that could be happening is that the torque converter locks or unlocks. In modern cars the torque converter locks under certain conditions, it improves gas mileage because you no longer invest gas into warming up transmission oil through friction.

jvring you hit the nail on the head. At normal driving, the torque converter locks up so you have a direct mechanical connection of engine to wheels. When you lift off the throttle the lock up is released.

While the torque converter is in the locked position the engine RPMS are pretty much dependent on how fast you’re going…the speed of the wheels. When you lift the throttle there is a few seconds delay (to avoid lock up hunting) the lock up is released. Now the engine is connected to the wheels by the fluid in the torque converter… the RPMs go up because of the primary/secondary coupling ratio in the converter.

The torque converter is really a torque multiplier. Trading higher RPMs for higher torque by the fluid coupling

This might be but why then would it do this 2-3 time before actually down shifting?
The engine RPMs rise for 3-4 sec. then settle back down for 4-5 sec. This feels just like a down shift with out the shift part.

Maybe it locking up again and again? I might have to take it to the dealer for this one.

thanks for all the help.
Q.

Without knowing the ECM/ECU mapping of the tranny it's anybodies guess why. I doubt very much the dealer will really know... the key word here is really.

With todays fly-by-wire transaxle drive trains, when we step on the gas we're just asking the computer to go faster. The ECM/ECU then makes the decision for what to do. Another factor is FWD transaxles are not as robust as a rear wheel drive, so specific precautions are taken in the ECM/ECU mapping so as not overload the drive train.

Many manufacturers have takeing a lot of grief with hesitation and shifiting problems because they couldn't get the mapping right with the drive train.

Now considering the ECM/ECU is controlling both the engine RPM AND the stage the tranny is in for any given situation, it's very hard if not impossible for folks like us to predict what the engineers where thinking in the mapping of the ECM/ECU.

I happen to be one of the unlucky owners of a 2006 ES330 Lexus. The problems Toyota has with their ESxxx trannys from 01-06 (along with Camry V6 owners) have caused their reliability downgraded by Consumer Report because of an awful hesitation when on and off the gas in stop and go traffic. There's a 1-2 second delay with NO throttle response, it then finds a gear and the throttle comes back with a a very disconcerting BANG. It can be duplicated but was/has never been fixed even after 2-3 ECM/ECU remapping TSB by Toyota. They even bought cars back from customers. BTW my Lexus has the same "feel" as you described when lifting off the gas... seems like theres a downshift.

This post has been edited by raw6464: May 7 2008, 07:44 AM

On my Nissan Titan PU, the electronic throttle and transmission are nearly seamless. Up shifts aren't noticeable and when braking, the transmission slips into a lower grade helping to **** forward motion. No hunting around.

I post this only to point out that it isn't just a common fault of fly-by-wire, but of poor mapping as was mentioned.

When I took test rides of '08 Azera and Sonata, I didn't notice this problem. Has Hyundai fixed it?

Red

Qman;

I think the posts about torque converter lock-unlock are likely correct. I had another vehicle that did this at about 45 mph., sometimes when speeding up very gradually or slowing down very gradually through an apparent critical point. That particular vehicle had no electronics controlling the transmission - just the hydraulics. Comments on forums indicated that there is usually about a 250 RPM difference from one state to the other. It could be that a pressure sensor on the trans-axle is sending false information to the on-board computer and causing the system to hunt for the correct mode. A visit to the dealership will likely reveal some stored codes that will help them find and correct the problem for you. The dealer may also have a device which can be connected to the transmission while it is being driven to further diagnose the problem. Temperature sensors are another potential problem area on transmissions too.

Make some notes before you take it in to the dealer as to whether it happens when the car is fully warmed up or cold, heavy traffic, level terrain, hilly etc. All clues may be helpful to them in diagnosing the problem.

So far on our new '07 Azera I only notice RPM stabilization points as the car progressively down-shifts while coasting. When speeding up slowly etc. the up-shifts are almost undetectable.

Good Luck! :mellow:

Joe