2000t4r

I just did my timing belt along with a new MAF and O2 sensor approx 3k ago. Just yesterday my CEL came on again, I had a chance to check the code today and low and behold its 171 again.

Does anyone have any ideads on what else could be the problem?

Thank you for your help.

2000tr

Bob_98SR5

did you pull the EFI fuse or manually delete the code using a code reader?

2000t4r

Yes the code was cleared from the data reader, then the CEL came back on with in 20 mins

UNR.Grad

I pulled a 171 code also, I upgraded the octane to 89 and it hasn't come back. Not the best fix, but good for now. I am going to clean the MAF next weekend and go back down to 87 and see how it goes.

2000t4r

Any other thoughts?

SpikeStrip

Clean the MAF well, and the Throttle body, then clear the CEL, Drive. If it comes back on, it's probably the MAF. If it stays off, it was a dirty MAF... Seems to happen more to trucks using a oil-type air filter.

MTL_4runner

......need a bit more info.

First, where was the MAFfrom? bought new at the dealer?
Same with the O2? which O2 was replaced?

Does this truck have a supercharger?

2000t4r

MAF was brand new from the dealer
O2 sensor was a denso also brand new. The primary O2 was replaced.

No supercharger

MTL_4runner

Ok then from what you tell me the next most likely source of a P0171 is a vacuum leak.
Check all hoses, lines, the throttle body, etc with carb cleaner to see if you can find a leak.

2000t4r

I talked to my mechanic and he said the samething about the vacuum leak, I will look into that tomorrow and will update you guys if I find the cause.

Thanks Yotatech.

Unhappy99

While you're at it, check to see that the new MAF's hotwires are clean and the MAF o-ring is making a good seal.

MTL_4runner

Also are you running a K&N air filter?
Just wanted to make sure it wasn't a MAF fouling issue.

2000t4r

No I'm running a stock type filter.

Type=Kragen

brandyn85

i have the same problem with a 99 4runner, 171 code, replaced the o2 sensor, and cleaned the MAF, the truck seemed like it was still ruynning weird, from a stop when you gas it feels like it wqants to bog down, then it picks up and goes... next day the light came on again, now its 171, and p0300 cylinder misfire... any ideas?

2000t4r

For the 171 try replacing the MAF and see if you get rid of that code. Also misfire could be a number of things. Also code 171 could be related to your misfire code.

MTL_4runner

Ditto......replace the MAF, reset the ECU and see how you do.

brandyn85

nothing but headaches with this thing...this is the first newer yota ive worked on... i have an 84 truck and 88 runner that was stolen about a month ago, so im used to the older stuff... so i unplugged the MAF yesterday to see what happened and it just died, so i plugged it back in... i reset the computer again with a code reader, and it just runs like crap now... at a stop it wants to die... and the CEL came back on, havent checked for a code yet tho. im going to stop and get a new fuel filter, another can of seafoam and run some of that through the manifold and the gas tank. also im going to do the plugs and wires... on the runner i noticed it only has 3 wires... and the 3 coil packs on the pass. side... do those packs just hook directly to the pther plugs? and are they known to go bad around 100k? it ust seems like its missing now.

MTL_4runner

Yes, they sit directly on top of the plugs for the passenger side bank. The misfire could be a bunch of things but it is hard to troubleshoot that code with a P0171 at the same time since they might be related as was mentioned above. I would change the MAF first, reset the codes and drive it until the CEL comes on again and then reread the codes.

Was the misfire p0300 or was there another digit on the end like P0301 or P0303, etc?

brandyn85

yeah it was p0300, i just checked it and it has a p0171, p0300, and a p1138 now

brandyn85

it was actually code 1133, not 1138. so tonight i ran 1/3 can of seafoam through the brake booster hose, and turned it off for about 10 minutes, started it and the smoke poured out for about 10 minutes. i put the rest of the can into the gas tank, reset the computer, drove it about 15 miles and still no CEL. im gonna do the fuel filter tomorrow just for good measure, i priced a few MAF sensors, and they are well over 200 here. so im still lookin for one. does anyone what exactly what code 1133 means?

P1133 HO2S Insufficient Switching Sensor 1