'07 Santa Fe "Bucking" Problem

188K mileage, but always completely serviced and run on Mobil One. Over the past 2 years, developed a Pronounced hesitation at startup and occasional bucking at a constant speed. Now, the Engine light comes on for a while, then goes off. Three dealers were no help! Plugs changed and oxy sensors checks out. Mileage dropped from 24 to 18mph for all around driving. Any ideas?

 

Interestingly, at 52000 the same problem. now for 5 years.---.Changed battery terminals, cleaned all grounds and new battery because the code which persisted indicated a low voltage problem to NO avail. The problem persists, so I'm looking for a solution also. But I have no start up problem. I think the next move should be in the emission systems

 

Assuming, crank, no start ...
Would go back to the basics first for the no start
Fuel
Air
Spark
Timing
Exhaust
Compression

If no spark and no fuel injector pulse then would suspect crank sensor.
But, need to test to verify the issue.

 

The car runs perfectly and starts perfectly, just intermittently -once or twice a month or even longer periods while moving perfectly will buck and almost stall, about a 3 or 4 second event, then pick up and run perfectly. A code may or may not appear and may even disappear. The code 2502. This issue for 5 years..

 

In post #2, you wrote "But I have no start up problem.".
Now, in post #4, "The car runs perfectly and starts perfectly".
I am no where near the vehicle. Can not verify the complaint.
And, story is changing. Sorry. This one is beyond me.

 

No change in the story. THANKS for the review.. You are not the first to be stumped.

 

"But I have no start up problem." ... oh, you mean you have no problem starting the car??
P2502 is an alternator, battery or wiring problem.
First would try tightening the cable terminals on the battery
And then inspect the alternator cable from the battery
Make sure the nut is tight on the terminal on alternator

Good luck

 

THANKS avisitor--all have been done including a new alternator (a recall by hyundai) and this problem persiststs