I had to replace my TPS (throttle position sensor) twice. I bought one from autozone for and I've been through a over a year with it an no trouble so far. Try all the free/cheap fixes first, and if those don't work I'd try this.

 

Update on problem...Gave TB and MAS a good cleaning. Surging has disappeared andperformance has increased...Thanks to all the folks who offered info...Love my STANG.

 

Well not too many are lucky when it comes to cleaning them. :P Well the free fix is to clean them, if that doesn't work then it should be replaced with a OEM. Some after-market parts are good but when it comes to sensors, I don't rely on them. I have a lot of after-market parts on a box that I've pulled from a lot of customer's cars next to my toolbox; is my collection. :P Build your FORD tough :P

 

What is water problem after rain?

 

Yeah, I decided to go a different route after both my FORD TPS' died. To each thier own.