Engine stutter/miss at moderate RPMs

DPRUST

MEMBER
1994 TOYOTA T-100
240,000 MILES

I have had a hard time diagnosing this issue. The computer is giving me a code 25 - low fuel/air ratio. The plugs, distributor cap and rotor, wires, fuel filter and O2 sensor are all fairly new. The problem is not consistent, it seems to stop at higher rpms and also idles fine. It has progressively gotten worse while i've been trying to diagnose it. The potential fixes aren't cheap: ignition box, maf sensor. I would greatly appreciate any suggestions. Thanks

Saturday, June 8th, 2013 AT 1:18 PM

1 Reply

KHLOW2008

MECHANIC
41,814 POSTS

Lean or rich mixture problems are never easy to diagnose as it involves almost every component in the engine management system. Below are a list of probable causes and the diagrsma shows how to go about. Hope they are helpful.

See if there is anything that you have missed out.

DTC 25, 26 - LEAN OR RICH AIR/FUEL MIXTURE

Probable Causes:
Loose Engine Ground Bolt
Open E1 Circuit
Short Or Open In Injector Circuit Or Injector
Fuel Line Pressure (Blocked/Leaking Injector)
Open Or Short In Cold Start Injector Or Circuit
Open Or Short In Oxygen Sensor Or Circuit
Coolant Temperature Sensor
Airflow Meter Or Air Intake Sensor
Compression Pressure
ECM
Vacuum leakages, (more likely to be between MAF and throttle body.)
Fuel pressure.

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