Just purchased a (well-used) 92 Miata. Already spent more than I paid for the car on basic repairs, but have an idle problem that has me stumped. When cold, the engine usually idles normally although it has it's moments and will die. However, after warming up, the idle rises to as much as 2200RPM and will not drop. My mechanic suggested the 'hot-wax' control valve might be the culprit but suggested I just turn down the idle screw located on the valve (front top of engine, left side) to get it through inspections since the part is expensive. Just for couriosity, I pulled the two air hoses connecting to the valve and squirted WD40 into it, which worked for a few miles but it quickly returned to its previous fast idle. Any quick fixes here, or should I bite the bullet and shell out the quoted $500 for a new part?

 

Check for a vacuum leak. If you use a dealer to do repairs you are most likely wasting money. Few dealer mechanics know the older Miatas. An older experienced mechanic might give you better results. Water in fuel will cause low idle speed and maybe the last mechanic turned it up to compensate. Start with the simple and inexpensive stuff before you spend lots on parts not needed. Good luck

 

it is never a good idea toloosen your throttle cable because your problem is still there.....it cannot be a vaccuum leak because a vaccuum leak will make the car idle at a lower rpm because you would be loosing compression and the car would run bad.....i would listen to your mechanic.....if you mess with the throttle at all, since the problem is still there, you may run into bigger problems later.....