2002 Infiniti I35 performance issues

[MonkeySnax]

Hello All! I've read several post to try and diagnose what's happening with my car but haven't pinned it down yet. A few months back the car started "spark knocking" as well as the performance dropping. It feels like I'm driving with the parking brake on almost, just rather sluggish. Normally I run 93 octane through it however occasionally I run 89 octane through it. Also it's almost stalling out at low idle when I'm stopped, it drops from just under 1000 rpm to around 500 and if I try to accelerate it doesn't do anything just kind of stutters. I can shift to neutral rev it a little then go back to drive and it's ok. It's got about 137,000 miles on it and I did replace the spark plugs last spring. I took it to a mechanic and he replace the alternator (said the voltage was too low which is why it was stalling out at idle) and the left and right upper oxygen sensors (2 of them) and added a chemical to break down the ethanol in the system. He also replaced the VIAS valve during all this. I will also mention that a drain got clogged somewhere in the AC system and got some rain water in it. The performance issues where happening before that though.

With that said, I've read some stuff about replacing the knock sensor and possibly the mass air flow sensor should those be my next steps?

[MaximA32]

Welcome to NICO! I would first check to make sure that there are no vacuum leaks and that the air filter is not clogged. There are only three things that will make a car stall (other than driver error) and that is lack of fuel, air and/or spark. You should be good with the new-ish spark plugs so that leaves the coil packs, the air intake or the fuel system. Are you getting a MIL(malfunction indicator lamp) on the dash?

[MonkeySnax]

Thanks! I changed the air filter with the last oil change (less than 1000 miles) and there was a check engine light on however the mechanic said it was the 2 oxygen sensors and has sense gone away after replacing them. I went ahead and replace the mass airflow sensor and the car is performing better however it stalled on me yesterday evening . I may not be describing it right but it never shuts off just idles really low and won't accelerate, it just stays at about 500 to 800 rpm and won't move. I can drop it into neutral and rev it a little then go back to drive and I'm OK. Could that be something transmission related? Not that I would know but it doesn't feel transmission related... It's still spark knocking a little when it's hot both as I'm starting it as I'm on interstate (70ish mph and about 2.5k rpm). Maybe I should try the coil packs next? There's more than one right? What about the cam idle sensor I read something about that too....

Thanks for your help by the way.

[MonkeySnax]

Well, now I've got a new twist with all of this. I'm starting to smell rotten egg's when driving it, more specifically when I'm driving and then slow down (i.e. transition from highway to stop light). Could that be the catalytic converter? Would that also explain the other issues? I read that it may be the battery but with the other symptoms I'm thinking it's the catalytic converter, anybody know how I can figure out which one is the culprit?

[MonkeySnax]

Whew, the rotten egg smell was coming from the battery (from early 2009, was time to replace anyways) gone now that it's replaced, hasn't "stalled" either.... but it's probably too soon to tell.