Ok,
I did a search on all of the above and didn't find the answers. I have an appt. in the AM at the dealer already since my "new" 3 week old (replaced 2 times already) flexpipe is rattling again and worse than the others! I'll provide the scenario to them at the same time about this.

Here's my scenario from today. Driving along at about 65 mph in 5th gear on the expressway with wife and kids in the car. 35 minutes into the drive the car did as described stumble/surge/misfire that is hard to describe exact but a noticeable feeling just not sure if it was speeding up or slowing down. The radio was off and you could hear the change in exhaust/motor noise. It did this at least a dozen times over about 5 minutes to the point my wife (who normally doesn't notice things like this) asked what's wrong with the car? Dropped her off at the doctor and waited with the kids for about fifteen minutes until she was done. Leaving the doctors office it did it a couple times while accelerating lightly in second gear and then again later also cruising on the expressway back home. The best way to liken the feeling was as if the A/C compressor was turning on and off on my old Corolla which had a lot less power and was noticeable if you turned it on while cruising. Haven't noticed that on the Sonata and my A/C is on very often.

I saw all the TSB reference's with O2 sensors on the V6 and the shudder (for automatics) etc but not many have the 4 cyl. 5 speed so reference base is limited. Just wondering if any others experienced something similiar. I might ask to change Fuel filter and return to me so I can disect it since the car has 23,000 miles on it already. What else? It just seemed to be as if there was either a fuel flow issue / spark issue / extra load issue that of course is now intermittent and did not trigger any check engine lights (yet).

This post has been edited by Sequoiasoon: Jul 8 2008, 02:50 AM

I had the exact trouble with mine, but the check engine light came on three times already. the dealership first said it was bad gass. then they said it was a piched wiring harness (whick was bogus) then they replaced the rear O2 sensor and the check engine light has not come back on. The strangest thing is this skipping of the motor when I rev it up to 1400 rpm. I was uncorfored by the service department as they said it was a characatire of the motor. Good luck.

Car is at the shop and they are working on it. Something A/C related as I was able to get it duplicate on a regular basis. Service manager said they are changing either the condensor or compressor but had to check with the tech (and the head SM) again. Something when the compressor was kicking in was causing way too much load and slowing down the motor. A/C was actually having problems at the same time which was why I went to dealer 2 days early. 95 degree daytime heat made the condition much more prevalent than my normal 70-ish night time drives.

Biggest part for them is they are trying to find out why I keep having problems with my flex pipe. As this is the third time they are changing it for the same issue. Supposedly I'm getting new mounts all around etc. at the same time to try and correct the problem.

My test drive to duplicate the rattles and surges was about 25 minutes long with the head Service manager driving. First he thought I was crazy until I was able to instruct him on what conditions (bumps etc) to get it to happen.

We'll see if it's fixed tomorrow or Thursday. At least they are trying and I get loaner cars while they try to correct it. Maybe I can convince them to just swap for an '09 Slate blue 5 speed manual if it keeps happening.

This is interesting. Based on similar problem I had with my good old V6 Accord, which was bucking at various speeds, I could also suggest a faulty speed sensor, though not sure if the Sonata even has one......... :innocent: :innocent: :innocent:

But, as always, MANY things good cause that problem (including bad gas, but of course).... A mechanic is shooting in the dark, while you, the driver, collects "data" to put 2 and 2 together, and have a better idea of what could be wrong.

Let us know, Sequoiasoon.