check and see if your fuel pressure regulator is leaking...if it's vacuum operated like mine, pull the vacuum hose off at the regulator end and start the car...if gas comes out the nipple then the regulator is bad....i just spent two months chasing this on my SF, a 2001 with 2.9 V6, car runs like a champ now.
apparently the FPR is a common problem on the early 2000 - 2003 years

 

Also, the FPR won't throw a code on the OBD II system, so it's hard to find...

 

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Hoping some of this excellent information will help out my issue. 2006 Sonata w/ 2.4 L has a misfire/shudder feeling only when load applied around 45 mph. No CEL. Tune up (plugs and air filter) done just a few months ago. Never got around to putting it on a scanner but I suspected a faulty coil pack. I switched the individual coil positions with #1 and #4 then switched #2 and #3 also. Misfire will now show up under load sitting in the driveway but not all the time. Shows up at lower speeds now too. I ordered a spark plug coil and installed it on the #2 cylinder for right now. I won't know until tomorrow if anything changes. I was curious to know if anyone tried this method. I see some users replaced all kinds of parts, 4 spark coils , O2 sensors, Cat converters, MAF's, timing components, trans services, fuel filters, reflash ECM's, gaskets ect... and still had problems. I'm just wondering if there is a common problem with these. Thanks.