'...felt like i was rear-ended...' help!

[ramenboy...]

hi guys, i mentioned in other post a little while back that i've got my trusty o4 vibe, and my brother had purchased an o6 matrix. well he emailed me with a problem, and i told him i'd post here to see if any of you guys had a similar experience and how it was fixed. thanx in advance:"...Frustrating news: In December before the holidays, I was driving it and a weird thing happened. I was starting from a stop at a red light, and suddenly the car lurched forward and felt like I'd been rear-ended. The only thing was that there were no other cars around me. So it's been at the service dept. since yesterday -- and they still can't find anything wrong or reproduce the thump. The whole thing is frustrating and annoying..."

[Mase]

There's nothing to fix. Just stand on the brake a little harder.It happens when you have an auto tranny and use the AC. When the AC is on it put a load on the engine and decreases the RPM. To compensate, the engine gives it more gas to bring the revs back up. When the AC turns off, the engine is still in overtime mode and the revs sometime jump for a second.That sudden release of the revs can produce enough power to the wheels to break the light amount of braking pressure you probably have applied to stop the car therefore causing you to "lurch".

[Vibr8tr]

By the sounds of it, I am guessing he was feeling a bit more of a jerk than just the AC, but that is a valid point, was it something that he would just be "overtalking"? If nothing else it could have just been something in the car that went, like maybe the computer read something wrong, or got some bad info, and shot some extra fuel in for no reason.... something like that. Who knows.... Wih I could be more help, but I think we all need more infor before an educated "guess"

[ramenboy...]

thanx mase, i'll pass that along. actually i'll try to get my brother to post up here.a little background: he's got an o6 matrix xr 4wd. does that make a difference?

[Mase]

It does make a difference. The AWD model has an auto tranny and supports my theory.Quote, originally posted by ramenboy... »thanx mase, i'll pass that along. actually i'll try to get my brother to post up here.a little background: he's got an o6 matrix xr 4wd. does that make a difference?

[ramenboy...]

thanx josh, thanx mase,yeah i agree a little more info from my bro will help. i'm trying to see if he's free enough at work to post here.thanx again guys

[ramenboy...]

hey mase,i could understand the lurch from the 'over revving', but what would constitute the 'thump'?

[Vibr8tr]

Maybe it settling or just the brakes or tranny catching.... I am starting to agree with Mase. I know that I can tell the difference in reving when I turn on my AC or turn it off, but I just never got any kind of movement out of it.....Who knows, honestly though, listen to mase more than me, he knows a bit more of what he is talking about.

[ramenboy...]

here's a link to what my brother posted on cartalk.comhttp://cartalk.com/board/showf...&vc=1

[Digger]

After reading the other post I would check three things. Drive by wire. first then the tranny is shifting correctly. sounds like it is is second and shifts hard into first. or your differential is bad but not sure if or how many we have on the AWD.

[ramenboy...]

thanx diggermy brother's taking a trip to the mechanic who used to service his celica. hopefully they find something, and then he'll take it back to the dealer fix.

[ColonelPanic]

Toyota, trying hard to appear smarter than everyone else because they can use fancy schmancy words... "operating to design intent" That sounds much more intelligent than GM just saying "uhh, that's normal" or "they all do that." lol!I wish your brother good luck! I don't have a clue what could be going on here, maybe the good mechanics at the other place can find something... This is a strange one.If it just lurched forward, I could see that considering how hard it was to keep my Vibe still at a stop when the engine idled fast. It felt like the brakes weren't capable of holding it back, I'd have the pedal smashed down and it still didn't feel quite stable. If he has brakes like that and the engine decided to get all crackheaded and make the RPM's surge, then I can see it lurching forward. Yet I still don't understand the noises or what was felt.Does the AWD stuff make any noises or can you feel anything when it engages?

[ramenboy...]

Quote, originally posted by ColonelPanic »...fancy schancy words... "operating to design intent" That sounds much more intelligent than GM just saying "uhh, that's normal" or "they all do that." ... hey cp, thanx for the good luck! yeah those mechanics. what can you do...the lurch and thump apparently takes place just after letting off the brake and when he hits the gas to accelerate.haven't experience the AWD...so i don't know how it feels during normal driving conditions.

[ramenboy...]

hey guys, quick update from an email i got from my brother:"...This morning I dropped off the Matrix to my mechanic's place. We went for a ride with me driving and him in the back seat. He heard/felt the thump. He just called me a while ago, and was able to reproduce the thump without even driving it (he explained that by stepping on the break in drive, then putting the car into reverse and back into drive again... or something like that) but he'll show it to me when I go pick it up in a little while. But anyway, he says it looks to be a issue of the transmission not smoothly transferring power to the differential..." he's gonna take it back to the dealer, and hopefully now, they can fix it.thanx for all your input. great bunch of guys we got here!