Low grumbling noise
 

I'm having this weird noise happen periodically when I start moving from a stop in 1st gear, or let off the clutch in 2nd after up-shifting from 1st. It's a low grumbling sound coming from the engine that sounds as if the engine is dying until the RPMs get up a little bit. I don't have a habit of lugging the engine, and it hasn't done this in the past. It seems to happen more often when the engine is hot, and under a load like having the AC turned on.

I have recently changed the plugs (NGK OEM), wires (Toyota), MAF (Toyota), PCV valve (Toyota), and cleaned the throttle body in my 1999 Tacoma. I also used some Valvoline fuel injector cleaner. Any suggestion would be great! Thanks.

OK; I'll try to be more descriptive. It's kind of like a choking noise. My crackpot theory is that it's not getting the right fuel / air / spark combo for this short period (2 seconds) of time.

Some people may think it's a rattle, some a suction noise, and maybe even grinding (not sure what it really is). So is there someone out there that has ever heard this noise, or have an idea as to what could be causing it?

Why did you change the MAFS?

First off, my CEL came on a few months ago. It was error code P0133 or P0130 (I can't remember exactly). After searching around, I read that it could be a dirty MAF causing the problem. So I cleaned it, and it seemed to make things better. Then a couple of weeks or so later, I started getting the knock again, so I cleaned it again, then again a couple of weeks after that. Each time I cleaned the MAF, it seemed (maybe it was just mental) to help out, but it never lasted, so I thought that a new one was in order. I put in the new one, reset the ECU, and that's where I am now.

The error code is sometimes triggered by the O2 sensor, but the CEL hasn’t come back on since the MAF cleanings / change.

Hmmm... actually, maybe the error code was P0171 or P0172. I'll try to find if I wrote it down somewhere. My memory's failing me now...