One of my cars is a 1990 miata and it only has 84,000 and it had the HLA problem a lot of miata's have. Through a miata forum I heard people using Marvel Mystery Oil so I tried it and it went away within 5 minutes of running. Change your oil and sub the marvel mystery oil for a quart of oil and it cleans the HLA out great. It doesn't hurt to change your oil again after you have driven a few hundred miles, but this stuff works great and you can even put it in your gas but use much less according to the bottle.