I have searched and found a few useful tips in regards to this situation but nothing 100% tells me how to fix this...

I recently acquired a 2003 GLS 2.4.. When its cold it idles silky smooth, but as it warms up and gets to normal operating temp and the idle speed drops it idles like crap (only in gear! in park or neutral again smooth as glass...) I have replaced the plugs with NGK Laser platinum (**** expensive!) cleaned the TB and MAF sensor. Replaced the PCV vavle, ran a can of seafoam through it. I replaced the wires with NGK's... It still idles rough... I checked the balance belt and its brand new, it still has the writing on it (Timing belt was changed at 94K miles)... Timing marks are dead on on the belt as well... Im now in the dark on this idle. The coils are good, sensors are good, and I have no codes stored in the PCM... Im at a loss... Is the 2.4 just supposed to idle rough? I really hope not (IMG:style_emoticons/default/sad.gif)

Maybe a 2.7 swap is in order (IMG:style_emoticons/default/biggrin.gif) any info on that?

Please help!

Our 2000 Sonata 2.4L /auto w/153,000 miles idles like a peaceful sleeping baby.
Sounds like you have a possible problem with timing belt if not replaced correctly will cause similar problems.

For quite some time I had the same problem. A discernable, slight misfiring at idle. Not violent shaking, but you could feel it in the pedals. My dealer said the car was running fine but did try to sell me a +$150 intake system cleaning. So I cleaned the MAF sensor and also the throttle plate. That helped immensely. Now sometimes you can hardly feel the engine at idle. Sometimmes you can... However, the biggest problem is still I'm stumped about is hesitations on acceleration through second and third. I am beginnig to think it may just be a bad computer design or programming. Considering I previousy changed the short block and rebuilt the injectors, and changed the coil packs and wires and MAF with no effect, I'm really wondering if its a design problem. I've got no codes so I'm at a loss. Dealer cant find anything either.

Im going to try cleaning the MAP sensor too. When I cleaned that on my Intrepid, the idle went from rough to smooth instantly. I have cleaned the throttle plate but it wasnt that dirty. Im going to completely remove the throttle body next week and clean out as much of that and the intake as well. I hope that I can get this idle situation figured out! Then I need to tackle the sway bar end links and bushings... I started getting a clunk today... Jacked it up and checked to make sure it wasnt the tie rods or ball joints, and when I got it up I noticed that the bushings are totally shot... I wonder why the dealer didnt notice this when they did the subframe recall? (Mine was still ok, so I got new drain holes and the coating...) Oh well it has 114K miles... what can I do haha.

But If I come across a V6 donor Sonata, that 2.4 is coming out lol! Its not fun going from 6.1L's and passing on the freeway with a little jab of the pedal, vs having to anticipate and hoping (although it does have decent pep)!

I haven't noticed any hesitation from 2>3 but from 3>4 it almost bucks into 4th when in regular drive. When you use triptronic it is fine, so I would imagine it is some sort of programming to help preserve the slushbox

I don't know. Mine is a stick, so it drives differently. The problems is in second gear while accelerating. Like a small hiccup while accelerating.

Your car shouldn't have that kind of bucking in the trans. Any firmware upgrades or TSBs on your model?

I have a new issue that started this AM. Once the car warmed up, it started bucking at idle in gear at stoplights, with a load (going uphill it chugs/bucks...) and warmed up it also does this in neutral. When its cold its not doing it.... This car and its idle problems are going to be the death of me.... The **** check engine light is not coming on.... I have a code reader and there is nothing coming up either... The timing belt and crank sensor was replaced at 90K miles and im at 115K now... And idea's?

Check engine light finally came on and it came up with a P0303. Misfire Cylinder 3. Pulled the engine cover, wire and plug, the gap was a little over .45. Regapped it to .41 and so far no bucking, but still vibration is felt at idle in gear. Pulled the timing cover and the timing marks are dead on and the balance shaft belt is on and lined up... This idle situation is terrible.

I have that same small hiccup on my 2002 5spd when accelerating sometimes.