the story is a bit long, but here goes, a few years ago we noticed a "bump" happening occasionally as we were stopped at a light. The car is a 2002 Hyundai Santa Fe. 2.7l. shortly after that we began having trouble putting gas in the tank. as "that" problem got worse, we ended up at the dealer to have the evap system redone. fill pipe and all. $800.00 the bump continued. so now it's about a year past the evap fix and the bump is worse than ever, just getting worse over time.. So, since there have been no codes presented and the mil light works, and I do have and use my code reader, no codes. So far I have replaced, alt as it was getting weak anyway, coil pack, and plugs. To see if the catalytic converters were clogged, I removed the o-2 sensors, and ran it, still bumping, cleaned mass air flow sensor with CRC mass air flow sensor cleaner, cleaned the throttle body, checked the throttle positioning sensor, still bumping. This bump is actually a hesitation It can be felt in the car best when in drive stopped. at the exhaust the hesitation bump produces a "smoke ring" on a cold morning. It might resemble a "miss" but again no codes. So I replaced the fuel pump
and strainer. Still bumping. On first starting, no bumping at all...as engine warms up becomes more and more noticeable..It only happens after the first few minutes of either run time or within the first few miles and gets progressively worse.. when at temp. the hesitation, even though fairly predictable at about 10-20 per minute, is random in the presentation..3 then 1 then 2 then 6 in a row, then1 then 2,ect.. Although it is felt better when in gear, it is not a trans problem as it is plainly noticed in N and P....however it then is central only to the engine..Recently on a trip to Wilmington (about 100 miles) we really noticed how the bump has developed into full blown staggering and stumbling on acceleration when in traffic as well as driving below about 35-40. On the highway, the stumbling /hesitation is not noticeable. even when passing. I hope you can offer a thought..thanks. Dave G.