99 Toyota 4runner limited


#1

I have a 99 toyota 4runner with 220,000 miles on it. I bought it cheap with the check engine light on. I believe the code i got was P0172 or 71. I replaced the O2 sensor before the catalytic converter and cleaned the MAF sensor. Check engine light still came on and fuel mileage is BAD. Any ideas? Engine also gives light sputter when tapping accelerator when in park.


#2

Code P0071 is for “ambient air temperature sensor range or performance” problem. This would need the wiring, electrical connector, and the sensor checked with a digital multimeter.
Code P0172 is for “system too rich”. The front oxygen sensor tells the engine computer, this; and the engine computer, in turn, tells you, with this code set. The old oxygen sensor was doing its job by reporting the information for the code P0172; so, why change it for telling the truth?

The engine misfire when you tap the accelerator, while in park, probably indicates a lot more misfire at other times while under way.
Tune the engine. Start with spark plugs, air filter, check fuel pressure, check ambient air temperature sensor and circuit, check performance of MAF, check engine coolant temperature sensor and circuit. The engine uses these sensor signals to control fuel injection.


#3

Very good advice from Helllokit. I was going to suggest checking the coolant sensor also. If it doesn’t work correctly the engine ECU could think the engine is always cold and make it run rich. That will degrade the MPG performance.


#4

Great advice and I thank you. I had new sparkies put in already and changed air filter which looked like “peep”. I changed the sensor only because the guy at Shucks auto supply, never told me the code but quickly seemed to point out the bad sensor which I then changed but light come back on. I went back for another reading and got the P0172. I got a fealing fuel pump might be week but that wouldn’t really affect fuel mileage, would it? Thanks guys


#5

A high mileage engine can have worn injectors. Cleaning and lubing them may help the engine run better. Try adding a fuel system cleaner to your next tank of gas and then add about 1/3 a quart of ATF for 18-20 gallons of gas next tank. After than add a few ounces of ATF every fillup. The ATF will lube the injectors and they should work better for a better running engine.


#6

What is the ATF you are talking about. I have used some injector cleaner and actually after I reset computer, I put 2 bottles into a full tank and light never came on until I refueled with just regular fuel. We have a local shop in town I heard they take out injectors and clean em up for 20 bucks a pop. I think I should have that done first.


#7

I cant seem to locate the coolant sensor. Where would I be looking?


#8

ATF is short for automatic transmission fluid.

Before you spend money on having the injectors cleaned I suggest you check the coolant sensor for the ECU and see if it is working as it should be. I would suspect it before a injector problem, but one of them may possibly be leaking. The sensor isn’t the same one used for the temperature gauge.

You would be wise in investing a service manual for the car to help guide you in the repairs. It is some of the best money you can spend on the car if you work on it yourself. The factory service manuals are the best, even though they cost more it is worth the extra money.


#9

Would you have any idea where that sensor is located? I looked around the other day and there seems to be endless wires and stuff. I’m good at a lot of things but when it comes to mechanical work, I really appreciate your guys’ help. Thanks. I will try the ATF next tank.


#10

WHY don’t you want to get the repair manual? It’s less than the price of a (probably needless) new oxygen sensor.

Tracing wires by their colors will help in finding components. For instance, the two wires going to the engine coolant temperature sensor are colored blue/black and green/red on the 2.7 L engine, and green/yellow and blue/black on the 3.4 L engine.


#11

I am definately going to get it. Just never crossed my mind untill you guys mentioned it. Any ideas on the best place to get those. Thanks guys


#12

Check yur public library. The library has repair manuals in book form and on web sites. Ask a librarian. Auto parts stores have them for about $18 U.S.

While at Walmart, pick up a digital multimeter for $25. It’ll pay for itself before you can say, “engine coolant temperature sensor and circuit tests”


#13

Alright guys, I got the repair manual, found the coolant sensor and did an ohm reading with a Greenlee CM-600 Meter I had. I got a reading of 376 about 45 minutes after my wife had parked the vehicle. Still fairly hot to the touch. The manual “normal ohm” chart is a kU chart ranging from 0.1 to 30. I’m not too sharp on ohms, can anyone do the math? Thanks guys


#14

I just found out this greenlee is AC only. Sorry guys, I’m gonna have to grab one from the store.