I have a new 2009 Sonata Limited, 4-cylinder. When I take my foot off the gas when approaching a stop signal, the car lurches as if the throttle was being pushed and pulled, or as if the transmission were shifting back and forth between gears. It happens between 35 and 50 mph. The dealership says that no codes are showing and thinks it may be the air conditioning cycling on and off, but that seems improbable to me. Does anyone have any ideas about what could cause this problem or how to diagnose or fix it?

Check your RPM. Is it jerking also, up and down?

There are reports on Lurching across the entire Hyundai Product line

http://www.hyundai-forums.com/index.php?sh...46&hl=lurch

Yes, what Miami linked to makes sense.... You know what, since my dealer performed the "38-42 mph vibration" TSB on my transmission couple month ago, the car HAS NEVER DONE IT AGAIN.... Shifting is smoother now.

But it could also be getting older. My transmission, I mean.

I think I have this problem also, only in 4th gear if I'm traveling around 35 and I left off the accelerator it feel like it slows down faster then I think it should... In any other gear it's fine though, I say it's something with the way the toque converter works.

I don't get a "lurch" (not the way I would describe it anyway), but I do have the torque converter lock/unlock thing. There's a stretch of road on my way to and from work that's 35mph. If I set the cruise at 40, it feels like the car keeps accelerating and decelerating, even though it's not. It's REALLY annoying, so I just set it a bit lower or higher (depending on my mood and on traffic conditions).

what u can do i accelerate a little over 40 for a quick second to get it to go into 5th, and then slow back down to 35.. car will stay in 5th until you hit 30.

Was that intended for me, Dj? If so, I've tried that trick both the way you mentioned and by using Shiftronic to keep it in 5th. Same results no matter what I do.

I had the same symptom... felt like it was down shifting when it wasn't. Took my 08 GLS 3.3 to the dealer and turns out it was the break switch assembly. Lurch is gone.

oops... replied to the wrong post.

This post has been edited by J-Rem: Jul 3 2009, 12:17 PM

I had the same symptom... felt like it was down shifting when it wasn't. Took my 08 GLS 3.3 to the dealer and turns out it was the break switch assembly. Lurch is gone.

There... right post now.

The BRAKE Switch (IMG:style_emoticons/default/whistling.gif) Was it turning on your Brakes??

By the way if you are speeding up it is a Lurch. If you are slowing down it is a...
LUNK

What I ment to say was it was a 'breaked' swith assembly... (IMG:style_emoticons/default/innocent.gif)

The 'lurch' I was refering to was what 'I' do when driving...

Yes, when it happens, the RPM jumps back and forth between 1,000 and 1,500. The dealership had it for two days, and all they did was top off the freon, because they speculated that the problem was air-conditioning related. The service manager rode with me today and witnessed the lurching and RPM jumping. But it only happened at the first stop and did not repeat. He now thinks it may be related to a bad sensor or a vacuum leak that only manifests when the engine is not fully warmed up. I am going to drive it this weekend and see if it follows that pattern.

Thanks to all for the other ideas, which I will look into. And if my problem gets solved, I will report it here.

After reading this thread I did a few tests on my Sonata. It seems everything reproduces best on a slight to moderate uphill, get the car up to 45-50 (switch to shiftronic to verify 5th gear if needed)
then let off the gas and watch the speedometer/tach
The speedometer drops speed depends on the incline
tach is a round 1000
right around 35 MPH the tach jumps to almost 1500
the speedometer is still dropping but there is a sensation of acceleration (lurching...) however it is very subtle
switch to shiftronic and it appears to be in 3rd indicating what I suspect is a downshift by design

This with a 4 month old Sonata GLS 3.3 V6. Does this mean something is actually wrong or is it just possibly an odd quirk about Hyundais?

Prior to reading this thread I had suspected my downshift should be a little less intrusive but never could put my finger on it.

Regards,


BT

This post has been edited by BasicTek: Jul 5 2009, 03:24 PM

Perhaps I'm not understanding this post, but I'm not seeing the problem here. Anytime you decelerate in a vehicle with an automatic transmission, the transmission will downshift to match the speed of the car. The "lurch" probably has something to do with the fact that you're on an incline. This sounds like normal operation to me.

What years/models does this apply too? Im curious about whether I should take my 2.4L 07 in.

Are you having this problem? If so take it in. And you can view any applicable TSB's listed up top

even though there have been no updates since the start of the Year listed here. Darn that Jerry! (IMG:style_emoticons/default/bwekk.gif)

Hey, I offered to turn it over to someone and give them the files and FTP access but no takers. I've got other TSBs to keep up with now, although they're very sparse it seems.

Well that's my question. My behavior seems to imitate the symptoms posted earlier in this thread but I'm not really sure it's anything wrong other than a somewhat overly sensitive transmission...

Was there money involved? I must have missed this transfer of power.

C'mon Miami....you can do this (you're the waterboy) for all of us.

Hatter does he need an HF badge to be in charge of TSB's?

No wait.....newsflash....or maybe a flashback.....TOMMER. He knows people who know people who don't like Lambo doors. Ya...that's the ticket.