Strange Issue - Seeking Suggestions
I have 2004 350z with 168,000 miles. A few weeks ago, the car was making a loud noise (like it was going to blow up) as I pulled into my parking space. I shut off the car and grabbed my OBDII reader. I started the car and the noise was gone...no codes. A couple weeks later it made the noise again (very loud, car shakes, etc), I shifted into neutral and rev'd the engine to 4,000+ rpm and put it into gear and it was gone.
Today on the interstate, it happened again. Car felt like it had a flat tire, shaking and rumbling, and again the loud noise. I shifted it into neutral and the shaking/rumbling feeling was gone (but the noise was still present). I put it back into gear, the loud noise and shaking (like a flat tire from the left rear). I put it into neutral and rev'd it over 4,000 rpm a couple times and it was OK when I put it back into gear. I drive over 20-60 miles a day and some days I don't have it, but when it does happen it goes away after revving the engine...driving OK after doing that.
I have no idea how to troubleshoot this and I'm looking for suggestions. The car doesn't have any codes, doesn't lose power, etc. The idle has been a little rough. By rough, I mean the RPMs aren't consist at idle (like it'll bounce between 700-730rpm for example, but will be consist at 800rpm when the A/C is on). I replaced the MAF sensor, cleaned the throttle body, replaced air filter, and reset the ECU. I don't think it's losing spark/power because the gauges/volts/etc are OK during the issue. My guess is it could be fuel, but it's happened over three or four tanks of gas from different companies (Exxon, Shell, etc). It only started to happen ONE day after I put seafoam in the tank. It never happened before that.