Hey Guys its been a while since last post. I have a 2002 4.7 with about 125k miles on it that while going at a steady speed will rev about 200RPMs for no reason. It doesn't matter what speed as long as its steady. It will rev 200 then drop down with no consistancy. It has been doing this for about 2 years. It stopped for a while and then it started happening again. I had a mechanic friend do a diagnostics on it and he said its not throwing any codes. I bought this truck brand new in 02 and put every mile on her and it has never given me a bit of problems (out of the ordinary). Any ideas? Thanks in advance.

 

When was the last tune up. Plugs, wires, throttle body cleaning. Run some sea foam thru the fuel system.

 

do you mean that the Tach reads 200 RPM when you are cruising?

That sounds like an issue with the Computer communicating engine speed..... might be crank or cam position sensor, or it could just be because the truck needs some new coils/wires/plugs....

 

I believe the last tune up was at 75k miles and it did include plugs, wires and fuel system clean. It has been a while since I ran seafoam thru it.
It jumps 200RPMs while driving so say I'm going 70mph and the RPM gauge is at about 2000 it will go up about 200RPMs and then goes back down to 2000RPMs for no reason. It didn't do it that often when it first started but now it is constantly doin it and its starting to bug the crap out of me. I'll get my mechanic friend to do a fuel system clean and see how that works. Thanks to all your replys.

 

Sounds like a Vacuum leak or a Throttle Body problem...

Clean the Throttle Body, and then check all of your vacuum lines for wear... if they are super stiff when you try to bend them they need to be replaced....