Hey guys ive been troubleshooting this one for awhile. while im driving my truck cruising between 30-50 (not in Cruise control) the truck will rev from like 1200 rpm to about 1500. the truck has had a tuneup brand new cat and im not throwing any check engine codes. I personally think its my o2 sensor any ideas, please help

 

I'm having the exact same thing happen. It tends to happen while gradually accelerating, usually once I'm over 50mph. Also notice it when climbing hills and taking long curves on highway. Thinking it has something to do with the computer regulating fuel/air mix incorrectly maybe. I've cleaned the throttle body and made sure intake was clear but it's still happening. Have you had any luck finding the cause?

 

Maybe ethanol surge? Possibly the tps but doubtful.

 

I would suspect oxygen sensors or EGR valve. Just because the CEL isn't on doesn't mean the sensor isn't bad, it's just not hitting the values of a completely failed sensor, they can be skewed pretty bad and still not set off the CEL.

 

My similiar issue was a dirty trans filter.

 

I think that was it for mine too. Had my transmission flushed and it hasn't done it since. Mystery solved!