Low Idle on humid days

First time posting here but I'm at my wits end. I have a 2001 3.4L Tacoma with 240k miles on it. It's a great little truck, but I'm having an issue with low idle at stoplights. I have been chasing this problem for a year now. No CEL. I have recently replaced the PCV valve and hose with OEM parts, took apart the throttle body and cleaned the IAC valve (the screws stripped, that was fun), changed out the vapor canister, replaced MAF sensor and TPS sensor. I've replaced spark plugs, wires, and coils.

Sometimes the idle will drop to 450-500 at stoplights and I can feel the engine bog down. It idles fine at startup 1200 - 1400. Also, it's hard to start when the engine is warm (it will start and immediately the RPM's are around 450-500).

I'm not a master mechanic by any means, but I like to do the work on these older trucks myself. The only other thing I can think of is a vacuum leak. Does anyone have any insight?

I live on the TX coast and almost every day is humid. Need help! Thanks!

 

Replaced the MAF with OEM or aftermarket?

 

Aftermarket

 

"That" may be the problem.

 

These ECUs are particularly sensitive to aftermarket sensors, or rather, aftermarket sensors are not as well manufactured as OEM parts.

I'd consider changing out the MAF and TPS with OEM parts (Denso is OEM if you want to avoid the dealer).

Vacuum leak could be part of the issue. At some point all the rubber in the engine bay just needs to be replaced.

The other thing I would consider are the injectors. OEM is expensive on these, but you can actually get better parts from MotorWest Performance- they sell a "upgraded Denso" set of injectors for a very reasonable price. Most of us here run them with great success.

 

It turns out the MAF is Denso, I thought it was aftermarket. I guess I had enough sense to get Denso when I replaced it. Sorry for the misinformation. And I know for a fact the TPS is OEM.

I took out the MAF and sprayed it with cleaner after someone mentioned that could be it. I drove it around and it maintained idle around 600 at a stop without bogging down. I'll drive it for a few days and if it keeps bogging down I'll look into the upgraded injectors.

Thanks for the great info! I'll post updates as I go.