Harsh Shift From 1st To 2nd Under Acceleration

[AustinGT]

Hey guys, don't want to be one that cries wolf for no reason, but today I was making a right hand turn and had to goose the LS a little to make it. It revved to about 2900 rpm in first, then on the upshift seemed to lose power and stumbled for a second before it shifted into second, but the car lost momentum and lurched forward until it caught. I tried to replicate the problem, and the only time it would do anything close was on another right turn under power, but it wasn't as bad. As you all know, the ecu cuts power for a millisecond to smooth out the upshifts, and it seemed like this time it cut way too much power. I don't think this is a tranny issue, but WWest said my earlier post on downshifting could be the result of u-joints. Could this be a u-joint issue, or is it an ecu problem? Any input would be tremendously appreciated so I don't over-react and have a coronary :(

[aarman4]

Is there a chance that your traction control system detected a slip and cut power on you?

[jcrome04]

Most likely the traction control, and also having the ECT in "NORM" mode would cause it to want to shift sooner.

Maybe you gunned it RIGHT at the same time the transmission was trying to up-shift.

[AustinGT]

Thankfully my car doesn't have TC (and 'cause I'm in the Valley it isn't needed)... The reason my first thought was the ecu was sometimes (like two or three times a month) when I cold start it, it stumbles for a second then catches and idles like normal. I thought that this most recent incident with the stumbling when shifting might me related... But the trans was in "norm" mode, so I will be careful to not have the throttle down when it is about to shift....

p.s.- if it is the ecu, could disconnecting the battery and resetting it help? Thanks...

[2rotor]

I use some "transmedic" or "seafoam transtune" 500miles before each trans fluid change.. Works wonders...

[AustinGT]

An update- I disconnected the battery this afternoon to see if resetting the ecu would help, the thought being to try easy things first. When I started it after reconnecting the battery, it fired right up and was fine. However, when I started it to go to class this evening, it stumbled again before catching and idling properly. The car upshifted fine, but one time I let up on the gas and it stumbled as the revs dropped. On my way home, as the car warmed up it stumbled big time then caught again <_< (it was in gear, so that should rule out the tranny). At this point, my guess would be some kind of sensor, perhaps O2? To wrap it up, whatever is wrong causes it to stumble upon startup, at one spot while warming up, and when upshifting under power. Any help is (and has been) greatly appreciated!

[jg4454]

Many people have posted that changing the motor mounts fixes this problem.

[nc211]

motor mounts really have nothing to do with a slipping transmission. It sounds like to me that your fluid is old and ready to be replaced. Use genuine toyota iv fluild, don't let some jiffy lube do the proceedure. Or, search for the drain n' fill proceedure, as it's been covered numerous times. Before you go buying expensive parts, start with the fluid first. The number 1 thing to bringing back a LS400 to near-new operational performance....is simply fluid.

[nc211]

I use some "transmedic" or "seafoam transtune" 500miles before each trans fluid change.. Works wonders...

2rotor, I think you're the first guy I've seen on here that's used the seafoam tranny stuff. I've been quite curious of that stuff, in particular, getting it out of the system when you're done. Do you have the tranny flushed of all quarts when you change your fluid? If it's anything like the engine stuff, I'm sure it produces great results!

[AustinGT]

It has been a while since I posted this, and should have wrapped it up earlier- my apologies! Anyway, I think I got some crappy gas- that sounds weird, but it only happened right after I filled up at the corner gas station (cheapest around). I used premium like usual, but it must have been something in the gas, because next time I bit the bullet and used Chevron, then Costco, and no problems since. At least that is what I am telling myself- I did check the transmission fluid and did a drain and fill, and it wasn't as bad as I thought (I am due for another oil change, and will do another drain and fill then). Thanks for all the input guys!