2NZ FE poor acceleration

[HaavardPYA]

Hi. I just bought an 2001 Yaris Verso 1,3 vvti. The acceleration is really bad and when i change gears on 50-100% throttle it jerks just when i release the clutch after shifting.

It has a bad exhaust, so can this be a problem coming from the two o2 sensors reading wrong values causing rich or lean fuel mixture? The yellow engine light also comes on after driving for about 20-30 minutes after resetting the ECU.

I have not had a chance to getting the car up on jack stands locating the leakage yet, but I will do it this weekend. Also going to clean the IAC, throttle body and MAF at the same time. The coolant level is at max in the expansion tank, but sometimes when cold, the coolant lamp comes on. OBD tool is allready ordered.

Something else you would recomend me to do at the same time?

best regards

[praivo]

when i change gears on 50-100% throttle it jerks just when i release the clutch after shifting.

Sounds like you're getting back on the throttle too late.

t has a bad exhaust, so can this be a problem coming from the two o2 sensors reading wrong values causing rich or lean fuel mixture?

Yes, most likely it would make it run rich because it would think it's running lean when it's not (due to the oxygen in the air drawn into the exhaust through the hole).

The yellow engine light also comes on after driving for about 20-30 minutes after resetting the ECU.

Can't tell much without knowing the code that activated it.

[HaavardPYA]

Originally Posted by praivo

Sounds like you're getting back on the throttle too late.

Thanks for the answer. I don`t think so, because it happens when i doing rapid shifts. Same thing happens when I´m driving on low revs and put the pedal down too fast. Maybe running rich then, as you said? :)

[Rednaz]

I have the same problem with my 2NZ but I suspect it may be my fuel pump failing? So I'm doing diagnostics and pump replacement next soon.

[praivo]

Originally Posted by HaavardPYA

Thanks for the answer. I don`t think so, because it happens when i doing rapid shifts. Same thing happens when I´m driving on low revs and put the pedal down too fast. Maybe running rich then, as you said? :)

More like running lean and/or not picking up throttle position changes quickly enough. Usually either a REALLY dirty MAF sensor or a bad upstream O2 sensor. On a Yaris it's more than likely to be the MAF sensor. I had to scrape the dirt off mine with a needle to really get it clean and working again.

[HaavardPYA]

MAF and everything on the intake side was very clean and nice. Donut gasket is shit so Ill replace it this weekend and see how it will run after that :)

[HaavardPYA]

So, I've replaced the donut gasket, upstream lambda and cleaned the maf sensor. Also checked for wacuum leaks. Still when engine is hot it stalls when I push the throttle from idle. When I disconnekt the maf it runs rough on idle and gets even worse so I guess my maf sensor is ok?

Got the P0171 code from the obd reader.

Any suggestions on things to check before spending 100$ on new sensors etc?

[B.B._07]

The stalling under load and the P0171 running lean code points to a fuel supply issue. I would rent a fuel pressure gauge (if possible) or go to a shop and have them read it for you. It's most likely your fuel pump is failing and can't keep up under higher rpm.

[2bz]

"Many people will replace the air fuel sensor or O2 sensor as soon as they get a bad reading, but the root cause is often a dirty or faulty mass air flow sensor or vacuum leak, thus causing the O2 or A/F sensor to read differently to compensate. Reading and analyzing fuel trims and the freeze frame data is the key to properly diagnosing P0171."

Fuel pump could be an issue also.