2002 Elantra won't accelerate when engine is cold and humidity is high

When humidity is high (80% and above) and the engine is cold, our 2002 Elantra won't accelerate properly. It hesiates for a few seconds and then all of a sudden it accelerates (usually 15-20 seconds after starting the
engine). This never happens once the engine is warm or when humidity is less than 80%. Unfortunately the computer doesn't detect a fault. Any idea what could cause that behaviour?
TIA
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There's a reprogram available for this condition ("warm ambient cold start stumble"). If you're within the 8/80 emissions warranty (includes ECM), your dealer should be able to reprogram your ECM for free to resolve this issue.
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I'm in Canada, therefore the ECM code isn't the same as US models. The service manager contacted Hyundai Canada and they told him what code to download. The issue has not occurred since the ECM was flashed, but the car now behaves sliightly different, i.e., acceleration is smoother than before. The service manager admitted that other customers complained about that same issue and that they could never totally resolve it.
At the same time, the dealer finally resolved the rear brake noise issue. Whenever we drove or braked at very low speed, we heard intermittent noise from the left rear area. It turned out there were 2 issues: the left hub had to be replaced and that corrected a faily loud noise at low speed (it did it without braking). A new strut corrected the noise when braking at low speed. Replacing the wheel bearing, the drums and shoes didn't help at all, but we now have brand new brakes in the back for free.
Thanks for your help.
Ghislain

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I've had this similar problem on my 2002 Sonata. I usually find that when this is happening, I run my tank close to empty, put in two bottles of concentrated Gumout Fuel Injector cleaner, gas up fully, and run the tank almost empty, it clears up. Some cars can be picky about gas brands too. You may also want to check on your air filter and air-intake chamber. Sometimes bugs, leaves, or other things are lodged in there and causing problems. You ought to be able to buy a 2-pack of Gumout concentrated injector cleaner at your auto-parts store. Beyond that, you may want to check your plugs or wiring and make sure they are not picking up moisture. Good luck.
- Thee Chicago Wolf
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The car only has 32,000 kms. The timing belt has been replaced after 4 years, the air cleaner is new, the gas is the same that we use in our other cars, etc. I'll let the dealer figure out the issue, but TSB 04-36-004 describes my problem.

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If your Sonata is a 4 cyl., there's also a reprogram for your car for a hesitation on cold start. It's described in TSB 02-36-037.
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