I own a 2007 Lexus GS350 automatic rwd with 105300 miles. I have observed the past few days the RPM fluctuate in drive and reverse. The RPM will usually sit at 650 in drive or reverse. At random times, I will hear a change in the engine operation and sometimes - but immediately - I will visibly see the battery light come on, dropping the RPM to 500. After a few seconds it will go back to 650. When this happens, if I shift to park, it should sit at 750-800 RPM but I have observed the RPM down to about 650. I observed the RPM bounce between 650, 500 and 750 in park, which is the first time that I observed this type of behavior. This behavior is not consistent. I also believe that the battery light comes on because the RPM is dropping intermittently and the only reason I am seeing the RPM drop after the light comes on is because the CPU reacts faster than the gauge. I am thinking it might be a bad MAF or possibly a slightly clogged fuel filter. I would appreciate any further guidance.