Tired of chasing drivability issue

hello. My 99 tacoma tends to run roughly when it's humid. I have recently replaced wires, ignition coils, fuel filter, plugs, cleaned throttle body, replaced tps, cleaned maf, checked vacuum lines, has new cat and 02 sensors. It runs awesome on cool or hot days if its dry, damp days kinda falls on its face, like its too lean. I'm running out of ideas. NO CEL's. Any ideas? Is it possible the maf or the AIT sensors could be sensitive to humidity? Every thing listed above has been done in hopes of correcting this, one at a time with little improvement. The TPS actually seemed to help but the next day the problem came back, much to my dismay. Please help. I love my truck and don't want to burn it under a bridge. Thanks...

 

At any time have you hooked a scanner up to see the real Time data ?

It runs rough ?? But it is not missing enough to trip the CEL/MIL ?? This does indeed work like it should ??

The light does trip ??

Just how much of a difference

Hot Humid Air is less dense then cool dry air but enough to cause major problems

 

I can't watch it real time, under the impression it is flaky but not out of range enough to trip the light. Right now its running kinda crappy as its kinda damp out. They want 100 bucks for the maf... yesterday it ran awesome, when it's running crappy it seems most noticeable under light acceleration, like when in traffic. When it runs good it runs greaaaat! Thanks

 

Well, I coughed up the 110 bucks for the MAF, no noticeable change. I haven't a clue at this point. It seems to stumble worst at rpms less than 2k, stop and go stuff. But if its warm sunny and dry it has always run well. It seems too lean. Sigh

 

You don`t mention your air filter has that been changed as well??

I could see a dirty filter might be enough to cause a difference in hot humid air.

Just a thought .

Automatic or manual??

ECT not shifting like it should feeling like it is the engine??

 

The air filter is new. Auto. Last evening I reset the ECM and it seemed to help a fuzz, of course that could be my imagination... It shifts ok, tranny is fine but at times it feels almost like you are starting out in third gear... like stepping on a marshmallow, shudders a little. Stop and go traffic is aggravating,its got 145k on it, has been well maintained. Went through all the vac lines. It can't be anything mechanically wrong cuz when she runs good, it runs amazing. Friggen drivability problems suck. I may need to buy a scanner and watch everything live. Coolant temp sensor and air intake temp sensors next...

 

Although you don't have any CEL's - I would go to Autozone and have them hookup and see if you have anything in memory.

Just some off-the-top of my head thoughts:

What kind of gas are you using? Not necessarily octane rating but 'cheap' gas versus other. Bad batch of gas?

Does it run like crap during idle? Or at slow speeds? Or only when you need power? Fuel pump? Dirty injectors?

Emissions is always complicated - but I wonder how you can check the system? I've heard horror stories of other vehicles having issues with bad charcoal canisters and blocked EVAP lines.

Do you have 4WD? Does 4WD work (vacuum lines at the front diff)?

 

So it feels like it's stuck in 3rd at take off? Entire truck shutters like when engaging a clutch?

Sounds like signs of failing transmission. But again only in humidity is strange.