Nissan pathfinder revs keep going up and down whilst driving?

Answer 1

Could be one of several sensors or a vacuum leak. If your check engine light is on you should buy an inexpensive scanner at your local parts store. Scanner start at about $60.00 and work on almost any car from 1996 and up. Key needs to be at the run position, engine off, and plug scanner into obdII port located under dash on driver's side. Scanner will display four digits codes whose meaning are given in the scanner manual. Replace faulty sensors and reset engine light. Resetting engine light takes about 30 seconds and step by step instruction are given in scanner manual. If check engine light is not on check for leaking hoses or gaskets. Hoses are easy to check just listen for a hissing sound and feel around connections for any sources of vacuum. Gaskets require a bit more knowledge of where to look. Intake or throttle body gaskets are typically the first place to check. An easy way to check them is to spray throttle body c leaner around the sealing area, if a change in idle occurs you found your problem. The spray momentarily seals the vacuum leak and returns the engine to normal idle. These are the basic steps any tech will take before moving on to more complicated diagnosis.