Replaced the fuel pump on a 2000 Dodge Neon to get the engine started. Upon start-up, the engine revs to between 3400 and 4000 rpms then drops to a sporadic idle of 1400 rpms after about 15 seconds. If you touch the gas pedal any at all, the engine revs again to 3400 p- 4000 rpms for about 15 to 20 sedconds then settles back to a sporadic idle of 1400 rpms. Wondering if this sounds like a sensor problem, a vacuum leak, or a fuel pump or system issue?.

 

Check for vacuum leaks and also clean the throttle body. Check engine light on?