99 Sonata Hesitation

Late last summer I posted about my 99 Sonata (2.4L) hesitating badly when started cold. It never actually cut off but came close. When warmed up it
ran fine. There were no CEL indicators. Most responses were to try injector cleaners. HyundaiTech also mentioned what it may be caused by and commented that if that was the case, then the problem would go away in the cold weather. What I just said is best that I recall, I have searched and tried to find that post/response but can't. On two different occasions, I put Chevron Techron cleaner in the tank and all winter it has ran fine when started up cold. I thought I had solved the problem, but how that the hot weather is back, it is coughing and sputtering again when started up cold. Runs fine when warmed up. HyundaiTech, do you remember what you may have thought the problem is and how to correct? thanks
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I don't recall my previous reply, but a quick check of TSBs indicates there's a reprogram for your car regarding an "infrequent cold-start hesitation." There are several reprograms for warm ambient temperature cold start hesitation on 2.4 Sonatas, but the one for the 1999 model year doesn't list any description of the ambient temperature.
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What's process to get TSB done on car over 10 years old?
wrote:

I don't recall my previous reply, but a quick check of TSBs indicates there's a reprogram for your car regarding an "infrequent cold-start hesitation." There are several reprograms for warm ambient temperature cold start hesitation on 2.4 Sonatas, but the one for the 1999 model year doesn't list any description of the ambient temperature.
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Take the car to the dealer, explain the condition, and ask them to check the problem and do the reprogramming if applicable. Expect to pay for the diagnosis, reprogramming, and any necessary and authorized repairs.
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