My 95 le model chysler neon makes throthing noise, automatically revs and losses take off power.?

Actually, this problem started on day after i change my connecting rods and pistons. i was on the high way when i noticed that the car had lost take off power. a friend said it was a fuel filter problem. i ended up changing my fuel pump. the problem is however still persistent. i had the injector nozzles sprayed clean, changed my fuel in case it was bad fuel yet it persisted. i have been suspecting my oxygen sensor. i still have the old one plugged. i had it cleaned and there was a bit of inprovement for a few hours. When i start the car in the morning, it will usually make some throthing noise and eventually rev very high and stabilise eventually. A mechanic mentioned it could be the iac valve but he is not sure. i almost got ran over by a lorry one day when i tried to overtake after a traffic jam. the car moved and suddenly lost take off power thus not being able to make a quick one. i was saved by grace. What could be wrong please. i need help