1994 Toyota 4x4 X-Cab SR5 with 214,000 miles. I take quite good care of my vehicle and it shows. Brought vehicle to Toyota dealer in Runnemede, NJ. Technician discovers that the large intake tube connected to the throttle body is cracked and causing a vacuum leak downstream of the MAS. Installed myself, code cleared. A couple days later the code returns. Back to the dealer and the Service Manager tells me that I need 1) new injectors, and 2) new spark plugs. I question him directly as to why I suddenly have (6) injectors which has somehow simultaneously all gone to **** and the spark plugs (Bosch Platinum) has suddenly stopped working? Slightly changes his tune and tells me now that they are "clogged" and the plugs aren't "hot enough." Cost to replace injectors was quoted at $1050 for just the parts. Didn't bother any more from there. Paid for the diagnosis and left.
Having a college background in chemistry and being the son of a 40+ year mechanic, I headed over to AutoZone and picked up (4) cans of Berryman Chem Tool Fuel injection cleaner, (2) cans of Gumout, and (2) cans of SeaFoam. Dumped the (4) cans of Berryman into the fuel tank. Ran the truck and emptied (2) cans of Gumout into the throttle body, and thew the remaining (2) cans of SeaFoam into the tank before filling it back up. Drove around the local highway, up and down [repeatedly] on the throttle get the solvents working.
Now, my feeling is that I was being ripped off by the suggestions made by the dealership. The plugs have been in the vehicle for 6 months without any problems. I also add fuel injection cleaner to the fuel at least a couple of times per year (mininum). I am also not sold on the idea that the NGK or Denso plugs are any better than the Bosch, as I have used them in other vehicles with absolutely no problems whatsoever.
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Re: Code 25- Lean Air-Fuel Mixture
Here is the real scoop form a real Toyota Service Manager, who is NOT interested in ripping you off or steering you wrong:
I take Bosch plugs out of engines quite regularly. Guys come in, with all kinds of lean codes, and I tell them that the plugs are incorrect. They are, in fact, not correct for your engine. I take out the Bosch/Splitfires/whatever, and put in the right Denso plugs, and everything is copacetic. Believe it or not, the engine IS designed with a specific Denso plug. Regarding the injectors, he is indeed ripping you off. Replacing 6 injectors for a code 25 is BS.
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Oxygen sensor signal
Water temperature signal
Intake air temperature sensor
Air / Fuel ratio lean
Vacuum sensor signal
Vehicle speed sensor
P0171------ system too lean bank#1
Po174------ system too lean bank#2
For these 2 codes, try cleaning the maf sensor (mass air flow), that is mounted in the big black hose that goes from the air filter housing to the throttle plate, if it is dirty, that will cause those 02 sensors to send a signal to the computor to lean the air fuel mixture. If cleaning it doesn't work, the sensors will probably need changing.
P0300---- Random/multiple cylinder misfire
P0316---- Cylinder misfire at start up---- first 100 revolutions.
On those 2 codes, you have to do some testing to find out why there is a misfire.
weak coil pack
fowling spark plugs/wires
Low fuel pressure
po171 means the air fuel ratio is lean (not enough fuel) so you must check for anything that can do that a good example would be a vacuum leak that allows non metered air to enter the engine (more air same amount of fuel = lean mixture) or a clogged injector (same amount of air less fuel = lean mixture as well)
if there is a miss when accelerating i would lean more to the injectors. but if you get the number to your toyota region office ask for an fts, or field tech, tell them what all is happening and that the dealer keeps jerking you around they will probably arrange for someone to look at it for at no charge. i work for a toyota dealer and they are really big on service like that.
25) is mixture control continuously lean
42) is VSS circuit - vehicle speed sensor
43) is starter signal circuit
Good luck and I hope this answers your question. And remember to rate all the solutions that you get, thanx.
Unfortunately, both of these items are equally important and repairs can't normally be avoided by taking care of your car.
Your MAP (Mass Air Pressure) Sensor measures intake manifold vacuum pressure to help control the air and fuel mixture and timing. It contains a pressure-sensitive element that connects to an electronic circuit, generating a signal that changes with pressure changes in the manifold.
Your EGR (Exhaust Gas Recirculation) valve recirculates exhaust gases through the intake manifold to be burned again, cooling peak combustion temperature. Dilutes the air and fuel mixture to keep the nitrogen oxide emissions within breathable limits. And yes, it could very well be that the EGR solenoid that is causing the issue.
Both units effect your vehicle's fuel/air mixture. This is important because your vehicle running lean/rich can cause "snowball" problems. For example, a faulty EGR can cause the vehicle to run rich/lean. If not repaired, in time, the exhaust caused by the wrong rich/lean fuel mixture can damage the O2 sensors and/or catalytic converter.
If I had to pick, I'd start with your MAP Sensor. One guess I would have is that your MAP Sensor failed and made your vehicle start burning the wrong fuel/air mixture. Assuming I'm right, this could have damaged the EGR Valve. So, I see no reason to replace the EGR Valve alone, just so it too can be damaged by the poor fuel/air mixture caused by the still-faulty MAP Sensor. If your lucky, you may see the faulty EGR code disappear once your MAP Sensor is replaced.