[kfx123]

So on cold starts, it revs fine at netural, but when I shift to first gear and step on gas, It seems to bogg and not do anything. After a while slowly goes back to normal, but before the car is fully warmed up it would just have a short period of no response then suddenly revert back to normal...

173k at the clock
unknown 2zz mileage
6 speed.

Cleaned maf, reseted the ecu I guess. Rotated the coil pack, if that even does anything.

Im assume either injectors or a vaccum leak?

 

[midshipmatt]

My 2000 is doing the same thing. Also cleaned MAS, reset computer after getting a reading which shows that I am running lean. I suspected a clogged fuel filter, but, it's in the tank and should self-clean. Maybe the pump is getting weak?

What doesn't make sense is that it does it mostly when I start it up and slowly goes away as the car warms up. But now it's not going away completly.

Has anyone else experienced this?

 

[midshipmatt]

Well, after researching, dirty injectors can cause this. especially when there is only 1 O2 sensor like on the 2ZZ. My 1ZZ has the PPE exhaust headers which also only uses 1 O2 sensor. This makes sense since a dirty injector does not atomize/spray well. When starting and running a cold engine, extra fuel is injected to make up for the poor atomization. In my case, the extra poor atomization on 1 or more dirty injectors is confusing the single O2 sensor. Then, when it warms up, fuel naturally atomizes better and the problem seems to go away.

So, Techron fuel injector cleaner should help. After adding this to the tank in the recommended amount, the engine improved each day like magic! I recommend trying this first before pulling anything apart. Of course a dirty MAF sensor also causes hesitation, but, this does not go away after it warms up.

Hope this works for you.
-Matt