P0171 & p0300

[lefty556]

It's late. I'm tired. I've read through a bunch of threads. I need some help.

I've got a 2000 SR5 5VZFE with Cali emissions, 258K miles. When I went to leave the restaurant tonight, it took considerably longer to start than normal. When she did crank, she was idling really rough. Almost immediately the CEL lit up. I drove it to the office and grabbed the code reader. It popped the P0171 and P0300 codes. When I went to leave the office, it was hard to start again and had a really rough idle.

I drove about 15 miles or so to a coworker's place so I could borrow his truck tonight/tomorrow. I stopped at multiple stop lights. While stopped, it was idling fine. No hesitation when leaving the light. The CEL stayed off.

At Ricardo's place, I tried cranking it after I turned it off. It was hard to start. The code reader shows both the P0171 and P0300 codes as pending.

Thoughts on how best to run down the issue? From what I've read, I'm leaning on the MAF being dirty or bad. Both the A/F and O2 sensors were replaced by me at 213K with Denso units. Fuel pump and filter replaced at 212K. I need to change the filter again, I know, but I haven't gotten there yet.

Thanks in advance for the help!

 

[spartacus]

It's late. I'm tired. I've read through a bunch of threads. I need some help.

I've got a 2000 SR5 5VZFE with Cali emissions, 258K miles. When I went to leave the restaurant tonight, it took considerably longer to start than normal. When she did crank, she was idling really rough. Almost immediately the CEL lit up. I drove it to the office and grabbed the code reader. It popped the P0171 and P0300 codes. When I went to leave the office, it was hard to start again and had a really rough idle.

I drove about 15 miles or so to a coworker's place so I could borrow his truck tonight/tomorrow. I stopped at multiple stop lights. While stopped, it was idling fine. No hesitation when leaving the light. The CEL stayed off.

At Ricardo's place, I tried cranking it after I turned it off. It was hard to start. The code reader shows both the P0171 and P0300 codes as pending.

Thoughts on how best to run down the issue? From what I've read, I'm leaning on the MAF being dirty or bad. Both the A/F and O2 sensors were replaced by me at 213K with Denso units. Fuel pump and filter replaced at 212K. I need to change the filter again, I know, but I haven't gotten there yet.

Thanks in advance for the help!

Cleaning the maf is always good also check for vacuum leaks cracked hoses and make sure your gas tank cap is tight. basically try to eliminate any unmetered air air getting into the intake..

 

[jgue467]

Cause of my 0171 was a cracked hose nearest to intake. Couldn't really notice it until separated from intake and pulled apart slightly, then there was a large crack letting air in. Replaced with OEM and like new, purrs like a kitten!

The 0300 is a general misfire, might go away when air intake leak is resolved.

 

[Devbot]

As said P0171 is more than likely a dirty MAF or vacuum leak. Given that P0300 means two or more cylinders are misfiring, and if it doesn't go away with P0171, I'd start looking at your coil packs/lightning hoses - our vehicles use waste spark ignition so each cylinder is paired with another, and off the bat that already sounds to match the issue. Could even be the sparkies themselves, when were they last replaced? Regardless I'd try and tackle this code second of the two.
To test for vacuum leaks simply spray some carb cleaner around the engine bay and listen for an idle change. It can either increase or decrease (though it will typically increase.) Most the time it's either from a cracked hose or a poor seal around the plenum.
It won't be caused by your AF/O2 sensors, as they throw totally different codes.

 

[lefty556]

I put on a new MAF and still had the issue. Sprayed some carb cleaner and it decided to act up when the carb cleaner got close to the PCV valve. I replaced the PCV valve and grommet. No joy. She’s hard to start and won’t idle.

I do have an exhaust leak. It’s leaking at the joint between the cat and the muffler (downstream of the A/F and O2 sensors).

The plugs and wires were replaced last year at 210K, so they’re probably due to be swapped out since I’m at 258K now.

Fuel pump and fuel filter were replaced at 212K. Both cats were replaced with Walkers at 213K. When I replaced the cats, I replaced the A/F sensor and the O2 sensor with Denso made replacements.

 

[FD7683]

I put on a new MAF and still had the issue. Sprayed some carb cleaner and it decided to act up when the carb cleaner got close to the PCV valve. I replaced the PCV valve and grommet. No joy. She’s hard to start and won’t idle.

I do have an exhaust leak. It’s leaking at the joint between the cat and the muffler (downstream of the A/F and O2 sensors).

The plugs and wires were replaced last year at 210K, so they’re probably due to be swapped out since I’m at 258K now.

Fuel pump and fuel filter were replaced at 212K. Both cats were replaced with Walkers at 213K. When I replaced the cats, I replaced the A/F sensor and the O2 sensor with Denso made replacements.

What brand were the coil packs and wires? I always suggest OEM parts. o2 sensors could be eliminated from the problem if they were replaced.

 

[19963.4lsr5]

P0171 & p0300

I put on a new MAF and still had the issue. Sprayed some carb cleaner and it decided to act up when the carb cleaner got close to the PCV valve. I replaced the PCV valve and grommet. No joy. She’s hard to start and won’t idle.

I do have an exhaust leak. It’s leaking at the joint between the cat and the muffler (downstream of the A/F and O2 sensors).

The plugs and wires were replaced last year at 210K, so they’re probably due to be swapped out since I’m at 258K now.

Fuel pump and fuel filter were replaced at 212K. Both cats were replaced with Walkers at 213K. When I replaced the cats, I replaced the A/F sensor and the O2 sensor with Denso made replacements.

Depending on how bad of a vacuum leak it was it may need to relearn it’s idle adaptive parameters.

I would make it a priority to fix the exhaust leak.


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[lefty556]

Depending on how bad of a vacuum leak it was it may need to relearn it’s idle adaptive parameters.

I would make it a priority to fix the exhaust leak.


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While I was going to the auto supply for a PCV valve and grommet, I unhooked the battery so that the temporary memory could clear. Like I said, the truck won't idle - it just stalls and dies unless you're on the gas pedal.

The plugs are NGK. I know I went with dual electrodes. I'll have to look at my notes, but I'm pretty sure the wires were NGK as well.

 

[19963.4lsr5]

While I was going to the auto supply for a PCV valve and grommet, I unhooked the battery so that the temporary memory could clear. Like I said, the truck won't idle - it just stalls and dies unless you're on the gas pedal.

The plugs are NGK. I know I went with dual electrodes. I'll have to look at my notes, but I'm pretty sure the wires were NGK as well.

That it’s self will wipe the adaptive’s and cause the engine to run on default parameters that may not work on a high milage engine.

Keep it running with throttle and slowly let off the throttle to let the engine try and compensate. If it can’t either clean your IAC and try again or do a compression check. A dead cylinder or three will act the same and not want to idle.


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[lefty556]

That it’s self will wipe the adaptive’s and cause the engine to run on default parameters that may not work on a high milage engine.

Keep it running with throttle and slowly let off the throttle to let the engine try and compensate. If it can’t either clean your IAC and try again or do a compression check. A dead cylinder or three will act the same and not want to idle.


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I fixed the exhaust leak last night. After putting the new gasket on, it fired up (took a little longer than normal) and seemed to idle fine. The CEL was on. I let it idle for 20 minutes or so. The CEL went off. I took it out for a test drive, some surface roads, some highway. On the way back to my buddy's place, I stopped and got gas. It was a very hard start, followed by rough idle and a CEL immediately. It drove fine to Ricardo's house, and idled just fine for a few minutes in the garage. I shut it off and pulled the code - still a P0171.

While on the highway, I did manage to get some data.


Idling at stop light:

STFT - 6.3%
LTFT - 39.1%
Calculated Load - 20
RPM - 607

On the highway at 60 MPH:

STFT - 1.6%
LTFT - 39.8%
Calculated Load - 34.1
RPM - 1970

Idling at gas station:

STFT - 4.7%
LTFT - 39.8%
Calculated Load - 15.7
RPM - 692
MAF - .5 lb/min

 

[LittleCaesar]

The fuel system is running way too rich per the LTFT.

Was the new MAF OEM or at least Denso? Can you get the MAF PID to read in grams per second by chance?

Get the 4Runner up to operating temp, then rev it to around 2000rpms and see what you LTFT values are.

 

[19963.4lsr5]

P0171 & p0300

The fact that your LTFT is the same at idle and at 1970rpm is interesting.

Are you sure you don’t have more exhaust leaks?

Or an Intake manifold gasket leak?

Having to add 39% more fuel than what it’s thinking is needed to me is more than a small vacuum leak.


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[lefty556]

The new MAF was a Denso.

I'm using OBD Fusion on the iPhone along with a bluetooth OBDII reader. I have no clue how to change it to read in g/s vs. lbs/min.

I don't hear any other exhaust leaks, nor can I hear it sucking air for a vacuum leak, but that don't mean much.

 

[19963.4lsr5]

If it was my rig seeing the LTFT at 39% I’d buy the special banjo bolt and check fuel rail pressure.


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[gamefreakgc]

Fuel trims maxed out.

P0171.

New MAF didn't change the issue.

Conclusion: a large vacuum leak! Find the offending hose. Try this technique rather than listening:


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[spartacus]

Ohm out the injectors to make sure they are in spec. the fsm says 13.8 ohms at 20*C ( 68*F). give or take a couple of ohms less then 12ohms cold or higher then 16 when hot would be a cause for concern. I would look'at the coolant temps when warm too. bad ECT can screw with a fuel trims as well as a stuck open thermostat. All that said, there was a thread on here a while a go where the symptoms were about the same and in the end it was a loose cranck pulley bolt that was the cause.

 

[lefty556]

Ohm out the injectors to make sure they are in spec. the fsm says 13.8 ohms at 20*C ( 68*F). give or take a couple of ohms less then 12ohms cold or higher then 16 when hot would be a cause for concern. I would look'at the coolant temps when warm too. bad ECT can screw with a fuel trims as well as a stuck open thermostat. All that said, there was a thread on here a while a go where the symptoms were about the same and in the end it was a loose cranck pulley bolt that was the cause.

Any idea which thread that is?

About a month ago, I replaced the radiator (it was definitely time), the fan and fan clutch (they weren't terribly expensive, and I was already gonna have a bunch of stuff pulled out) and the belts. Since then, the alternator belt squeals a bit at startup. I've tightened it up once or twice, but it keeps happening. I wonder if they might be connected...

 

[spartacus]

Any idea which thread that is?

About a month ago, I replaced the radiator (it was definitely time), the fan and fan clutch (they weren't terribly expensive, and I was already gonna have a bunch of stuff pulled out) and the belts. Since then, the alternator belt squeals a bit at startup. I've tightened it up once or twice, but it keeps happening. I wonder if they might be connected...

It took me a while to find it but here it is.
Running Lean and misfire

 

[desertegal7]

I would advice to check valve clearances.. my 2.7 rough idle when cold for like 30 seconds then back to normal.. same codes i got.
put a paper on exhaust and if it getting sucked the valve issue for sure.
adjusted valve clearances and run perfectly afterwards.