one more thing to consider/check - the AOS. Have you or was it ever replaced? Pull the j-tube off the side of the throttle body and see if there is any pooling of oil in it. There should be a film but no pooling in it. Also, while the car is running, try and remove the oil filler cap. If it comes off relatively easily, you should be fine. If you have to fight to get it off, the AOS could be going south. If functioning properly, the car will stumble when you remove the oil filler cap. If it runs better when removed, then you have a problem.
If pooling oil in j-tube, you'll want to change the AOS PRONTO (~ $120 in parts and 2 hrs DIY). Then clean the throttle body.
Let us know what you find and good luck.
