What’s wrong with my airplane?

Here’s a question that was recently sent to me:

It has happened to me twice recenely. I fly a Cessna 172R (1997). Under very normal weather conditions at low altitudes like 2,000 to 3,000 MSL, the RPM ramps up very high getting into the red zone and I have to pull the throttle back to almost half position to get it down to maybe 2,300 RPM.

First, my disclaimer: I am not an A&P mechanic.  However, I did stay at a Holiday Inn Express last night so…

No seriously, I’m not sure what is going on here.  This is a unusual problem to say the least.  I ran the problem by my friend who happens to be a IA with some 172 experience and he thinks that you may have a problem with a clogged fuel injector but he is merely guessing.  It might be that you are only operating on 3 cylinders and suddenly the fourth injector becomes unclogged and comes firing away.  If it has happened twice, you definitely need to take your airplane to a trusted A&P.  If it is a rented airplane than you should fill out the appropriate squawk form and report the malfunction.  I am very curious as to what the problem might be.  Be sure to drop me a note when you find out what is causing this.  Sorry I can’t be of more help here.

Fly Safe!