1999 hyundai sonata gls v6February 10, 2013My cars runs rough at idle while in gear. It runs smooth when I put it in neutral or park. What should I check? Keywords:Rough IdleSonata 1 thought on “1999 hyundai sonata gls v6” Freeautomechanic February 10, 2013 at 12:11 pm First, if the check engine light is on, you need to pull the codes and post them back. If there is no check engine light on, The first thing I would do is to clean the throat of the throttle body so that your idle smooths out. I use brake wash and a rag, engine not running. Clean the throat with the butterfly held open and around the butterfly. This should allow a little bit more air in that it once was able to. The Second thing to consider would be when the last time you had a simple tuneup? If it has been a while, you might want to through in some new spark plugs and check you air filter for replacement. Comments are closed.