Po171 Blues... NOT MAF Sensor. Hard Start, No Start

[denvertoyota]

Hey guys, got a issue maybe somebody could give me new insight on...

I guess I shall start a few months ago. I used to get hard to start issues when it was warm. It would eventually crank and run, but i had to give it fuel for it to get started. Once started, no driveability issues.

Two Weeks ago, i was idling with A/C on, and when I went to drive away, I stalled.

NOW, the last couple days I have been searching the forum in regards to the P0171 Code with is "lean bank 1" and I found a few things. One, Clean the MAF. I cleaned it. Two replace the MAF. I replaced the MAF with a used one from a toyota yard. Three, clean IAC. I cleaned IAC per instructions in a write up. Number 4, replace fuel Filter. I replaced the fuel filter, have a new tune up, one new 02 sensor (pre cat).

I take care of my truck, and this issue seemed to be compounded after towing a heavy trailer for some distance. It was fine that day, fine the next day on the way to work, than gave me trouble on the way home and thats when the light came on.

It will idle perfectly fine when running. When I give it any fuel it doesnt change the acceleration, and will bog or pop under full throttle or rev up through the RPMS but not go any faster. I started it this morning, started ok, ran ok, still no good acceleration tho, so I drove to my parts store to get said fuel filter. When I came out, it would not start. had to wait over an hour, and it finally started, and idled great but still, no acceleration.

Aside from replacing the IAC which seemed to be fully functional, the throttle position sensor, or I could possibly have gotten a bad MAF again (unlikely as the issues are exactly the same with both MAF sensors) I am at a loss for what to do next. Been three days of working on it, and I have searched the forum pretty well before posting...

Please Help! :smashputer:

 

[denvertoyota]

So it wasnt starting for awhile... it finally started, runs rough. I pulled the plug to the TPS and it ran the same. So I put the plug on and off a few times while giving it gas, and it would rev up, and finally ended up at a reasonable idle before I shut it off, but still had boggy acceleration.

Once before I pulled the plug to the TPS and sprayed with MAF cleaner and it got better as well.

Anyone think it could be the TPS? I am assuming it is this but I have put alot of money out chasing causes already. I am not very technical with testing these things, but if somebody could point me to a written way how, that could help also.
Thanks
Rob

 

[kball]

p0171, 99% of the time, is either the MAF, pre cat O2 sensor or a vacuum leak. If your O2 sensor is original I'd replace it since it's way past the life expectancy. If that doesn't help I would think you have a vacuum leak.

 

[denvertoyota]

Just replaced the TPS as well.... No luck. I replaced the rear O2 sensor a month ago, didnt do the front. Maybe its that...turning into a money pit I tell ya

 

[denvertoyota]

On the bright side, a new DENSO O2 sensor on advance was $112 but I found a coupon for $40 off $100 purchase. Just googled " advance auto parts coupon"

Same with the TPS. Was $55, got it for $35. Wish me luck, will be replacing the O2 sensor tonight.

 

[denvertoyota]

Just remembered after getting back with the new O2 that it was the pre cat O2 sensor that I already replaced last month....

Any other ideas?

 

[kball]

Vacuum leak or both your MAF's are messed up. There's copies of the FSM online. Search for it. It has instructions for testing the MAF sensor. If it turns out it's neither of these the FSM says it could be things like the coolant sensor or the ECM.

 

[denvertoyota]

Thank You! See the problem I am having now, is it is sitting outside running and idling perfect right now. No Check engine lights.

I was able to pull some data from my scanner in this state. It is running and idling perfect at the moment. That is why I don't think its a vacuum leak....

Here is the DATA. I am not great at decoding the info:

700RPM
Load Value 14.5%
Coolant temp 199
Short term fuel trim 19.5%
Long term fuel trim 19.5%
Ignition timing advance 9% plus or minus 2%
Intake Air Temp 98
Airflow rate .43lb/min
Throttle position 10%
02 Sensor 1 .035v
02 sensor 2 .040 U
Idle Air Motor Duty Cycle 33.1%
Vapor pressure -25.09 psi
Injector pulse width 4.0ms

 

[kball]

I'm no expert at reading those numbers either. I think they look good though. Wait and see if the CEL comes back on and if so get it scanned to make sure it's still the same 0171.

 

[denvertoyota]

Still, even idling and running great, the second I give it throttle it bogs and if I give it to to much, it seems like it would die.

Im at a complete loss...

 

[denvertoyota]

I'm no expert at reading those numbers either. I think they look good though. Wait and see if the CEL comes back on and if so get it scanned to make sure it's still the same 0171.

P.S. How do you like your treadwright tires? Was considering them.

 

[kball]

How exactly did you clean your MAF? Just trying to make sure you cleaned it right. Not to insult you.

I love my treadwrights but shhh, don't tell anyone, it pisses them off.

 

[denvertoyota]

How exactly did you clean your MAF? Just trying to make sure you cleaned it right. Not to insult you.

I love my treadwrights but shhh, don't tell anyone, it pisses them off.

Well I cleaned my old one with MAF cleaner, sprayed down in the hole where the two wires are, swooshed it around, sprayed direct etc. Its a 98 so its the cylindrical type that is not removable. I then went and got a used one, and cleaned it also before install. Same exact problems to the T with both parts.

 

[kball]

It sounds like you cleaned it correctly so... I don't know either.

Here's the checklist for the P0171 code in the FSM.

 

[denvertoyota]

It sounds like you cleaned it correctly so... I don't know either.

Here's the checklist for the P0171 code in the FSM.

Thank you for that... A few things on there i havnt tried...

 

[PitbullRescuer]

If it idles okay but bogs under throttle, I'd suspect either MAF or TPS. But, to rule other stuff out:
What brand O2 sensor did you buy?
How dirty was the MAF? (You sure it's clean)
How's your air filter look?

I'd suggest Seafoaming it as well, through the gas tank. Can't hurt to clean out the line and injectors.

 

[denvertoyota]

If it idles okay but bogs under throttle, I'd suspect either MAF or TPS. But, to rule other stuff out:
What brand O2 sensor did you buy?
How dirty was the MAF? (You sure it's clean)
How's your air filter look?

I'd suggest Seafoaming it as well, through the gas tank. Can't hurt to clean out the line and injectors.

I hear ya, thats why I tried that first.
o2 sensor is oem denso and has been on the truck for over a month as preventative maintenance, not due to this current issue.

Maf was not to dirty, I cleaned it very well, and THEN I replaced it. I also cleaned the replacement MAF.

I also replaced TPS with a brand new one.

Air filter is new. Anything tune up wise has been done.

Ive run seafoam twice in two years. Most recently 4 months ago. While doing all of this in the last few days, I pulled the throttle body and made sure it was spotless as well as disasembling and cleaning the IAC. The intake itself was very clean inside.

Thanks for the insight guys.

 

[denvertoyota]

Anyone thinking fuel pump or coolant temp sensor? Anyone had these symptoms and they were fixed with either part?

 

[denvertoyota]

Just decided to send it in for service. I will update this thread with the results...

 

[hambob]

I voted fuel pressure.