GreggyG

What could cause this? I have 100k and I only notice this if in park or neutral at 1500rpms. It goes away before and after and it seems to drive very smoothly. I had a bad alternator and I just replaced it but the "new" one is making a high pitching ringing so I'm having the shop change that out for a new oem. Any chance it's the alternator or could this be something else. I have sea foamed the throttle body recently and cleaned the maf recently and changed the air filter. I didn't do plugs but they are do at 120k

GreggyG

Forgot to mention that I just had the timing belt done by Lexus, I'm not 100% sure if it was doing it before that.

GreggyG

update, I went ahead and changed the plugs tonight. it improved the stumble by 60-70%. It was fairly noticeable and now its faint. I still notice it (i guess because I'm looking for it). I noticed that two plugs on the driver and passenger side closest to the firewall had a little oil on the threads. I also noticed that two plugs (one on each side) were barely hand tight, loose actually. Anyway, the only other thing I can think of is that maybe the MAF sense has a "flat" spot in it or something? Or maybe as it it gets older, cleaning it can only do so much? Either way, I'm open to more suggestions. Thanks.

techrep

You can clean your MAF sensor...ensure you use a good MAF cleaner like CRC brand.

GreggyG

any chance that this is connected to a motor mount or transmission mount?

techrep

Did you ever clean your MAF sensor ??

GreggyG

yes, thank you, I should have mentioned that was one of the first things I did. Here is an update though, if I am not just imagining this, the vibration seems to have gone away after I just installed the secondary air pump bypass and installed the block off plates. It was still doing it after the initial electronic bypass, but it seems to have disappeared now for the moment since I put those plates on. I wonder if/how that could be connected?

BlackCat81

I had a very similar issue on an old Infiniti G20 that had EGR issues. Same thing. As soon as the EGR opened, it misfired. I ended up creating some concoction of vacuum lines that sort of let it work enough for emissions, but got it to not stumble. No idea how I did it, but it was last year and I haven't seen the car back. EGR issues can do weird stuff, and are tricky to diagnose.