I did an oil change on my 1.6 protege. i used a heavier oil than i normally use but still one recommended by the owners manual. The next day the car would not want to run over 60mph. It does not want to hold a speed it would feel like you thew out an anchor and it would drop 5mhp. It also seem to have spots in the rpm range while accelerating when it loses power. Torque seems to drop at low RPMs while the motor stumbles. THe first thing i did was change the oil again to the normal grade. I also have changed the air cleaner and the spark plugs and none of that helped. It also drops down to less than 100rpm at stop lights and it has just stalled once. I does not sound bad at idle or when revved in park nor does it vibrate. Any suggestions would be helpful.

The oil had nothing to do with the symptoms you're now experiencing, so look for something that may have been damaged or accidentally disconnected when you did the oil change. Vacuum hoses would be a good place to start looking. If you don't find anything obvious, take the car to AutoZone and have them read the codes for you.

It was the MAF sensor. I just took it out and cleaned the filaments with a soft paint brush and it was fixed. I did not have a check engine light on with all of these problems so I could not get the codes read.