Surging Sonata

The car runs smooth when idling, runs smooth when accelerating, but as the
car gets close to the desired speed, it starts dropping rpms, then surging
back up again. It's really hard to drive because the car is continously
jerking.

With the cruise set at about 73mph, it was running at about 2900rpms then
it was hesitate the rpms would drop to about 2500rpms, it would surge back
up to about 3100 rpms and then level out to about 2900 rpms. The intervals
between it doing this would depend on the road (going up/down hills or
flat surface)I would guess at least every 45 - 90 seconds. (Note: It does
NOT matter what the speed I'm driving at, it continously does this. Also,
the car will not shift gears until it reaches about 4000rpms regardless of
the speed of the vehicle)

I recently replaced the throttle position sensor (28 August 07) and the
throttle body (22 September 07. After I replaced the throttle position
sensor, it stopped surging for 1 day, after I replaced the throttle body,
the car ran great for about three weeks, then it started surging again.

Could anyone offer any assistance or advise to resolve this problem? I
would really appreicate it.

Tks, Mark

 

It would help if we knew a little more about your Sonata, What year? What
motor? What kind of transmission?

Rob

 

Have you scanned this car yet? Sounds like the lock up is acting up, but
I'm wondering what's going on with the high shift points.

 

Like Mike said, it sounds like the lock up converter is going in and out.
It used to be that cars had a vacuum actuator for that function and
sometimes the line would leak.
How many miles are on it and what year? It could also be a plugged
catalytic converter which would cause you to use a lot more throttle and the
transmission may think you want to downshift. The easiest way to check that
is to put a vacuum gauge on the intake manifold somewhere and see if the
vacuum is up around 27 inches or so or down a lot lower. If it is real low,
your cat is plugged.

Tom

 

Rob,

It's a 2004 with a 2.7L V6 and automatic transmission.

Tks, Mark

 

Mike,

I had to scanned in Miami at the end of August (30th), which showed
throttle position sensor was bad. It was replaced them and the throttle
body was replaced about 3 weeks ago.

I'm having scanned again this weekend, I'll update this on Saturday or
Sunday.

Tks, Mark

 

Tom,

Thanks for the information. I'll have it scanned again this weekend
and get the codes. I'll also research the Cat/Vacuum route.

Tks, Mark

 

Mark:

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