Hello. We have had our 4Runner for 10 years now. About 8 years ago we knew something was wrong. We took it to 3 different mechanics who spent over 3 straight days of diagnostic repairs & over $1200 to be told IT WAS IN OUR HEAD!!! We knew it was not & started to replace things trial & error. Everything we have replaced since has made a difference & improved the 4Runner, but never fixed it. We had poor acceleration, loss of power, chalk white NGK Plugs, extremely poor gas mileage (about 200 miles per tank when it started to only 136 miles per tank as of today) This has been a problem for 8 YEARS!!!! The check engine light never came on until last night. it threw code 25. We have replaced EVERYTHING it could possibly be except for Distributor & ECU. We replaced Cat, Throttle Position Sensor, Coolant Sensor, Mass Air flow sensor, Coil, NGK plugs religiously every 3k, new wires every 3k, Oil & filter every 3k, a used o2 sensor (this was only used part purchased). Yesterday it threw code 25. we replaced the MAF just this morning & Check engine light went out for 40 miles. Then it came back on, from what I gather & everything we have replaced, the o2 sensor has an open circuit & is throwing the code. We are going to be checking o2 value tomorrow & hopefully finally after 8 years fixing 4runner. Everything we have changed has made drastic improvements to her but we knew something was still wrong. If we replace O2 sensor tomorrow & it still is on my husband & I are CLUELESS!!! We will then go with the distributor & ECU or think possibly intake leak. We are both in agreement we think its running lean due to o2 sensor. In your case you may want to consider changing the TPS. It can be difficult to set. My husband set 2 days trying to set all 5 values, then I came & set all 5 values in about 20 minutes. TPS are tricky to set & many people never get all 5 values matched. I can tell you personally from research its best to get all values set so it ensures a steady normal idle once installed. The only thing is all the parts are pricey. To save you money you may want to over ride ECU & check the code its throwing yourself. Dealers are the biggest rip off artist you can find. Good luck to you. Hope we both fix this stupid code 25. God Bless.
Code 25 air fuel ratio lean condition indicated.POSSIBLE CAUSES- AIR LEAKS IN THE INTAKE MANIFOLD -EXHAUST MANIFOLD -EXHAUST PIPES- FUEL CONTROL SENSORS IS OUT OF CALIBRATION LIKE THE-ECT IAT MAF -LOW FUEL PRESSURE LIKE- FUEL FILTER CLOGGED PRESSURE REGULATOR FAILURE- ONE OR MORE FUEL INJECTORS RESTRICTED -HO2S ELEMENT IS CONTAMINATED DETERIORATED OR HAS FAILED -VACUUM HOSE IS DISCONNECTED BROKEN LEAKING OR LOOSE.
Heads up! Know what each sensor does. It will narrow yor field of componants in suspect. You have mention everything but the intake air temp sensor and the coolant temp sensor. These two sensors actually enrich the fuel for cold running, both mechanical and operating envirinment.I could list the rest but you have covered them laready. So, good luck
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