Any ideas what it could be? Car is stock.

 

...uh wow, be more specific?

if it idles high, with my last car I heard the butterfly sticks open a little and thats what causes that but I have no idea if thats true or not.

 

have you checked for vacuum leaks? does it get better as the car gets warm?

 

Check the water temp sensor!

 

It does get better as the car warms up. I recently removed a supercharger from the car. Had the same issue with that on the car.

 

one of your muffler bearings could be going?
or your noodle valve





on a more serious note, check the following,

coolant level
idle near throttle body
clean iac thingy
maybe throttle cable too tight?

if all else fails, replace throttle from your car, to that of a miata with a lower idle, i had to do this to a friends car, after trying everything else, somthing was wrong with his, and to this day, we have no clue what it was

 

check out mr. fusion. If he's not getting enough fission, it will idle rough.

 

O2 sensor???

 

Call Matt out of Worcester at 508 873 7314 and tell him to sell you some parts.
You can also find him here... http://cgi.ebay.com/ebaymotors/1990-...mZ120264387154