2001 Ford Ranger
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P0171 System Too Lean - Bank No. 1.
P1506 Idle Air Control Over Speed Error.

Hi! So here's what happened: I play music off my phone through an auxiliary cable to the stereo. I didn't realize I had the volume on my phone turned way down and had the volume of the stereo turned way up. Well I went to plug in the auxiliary cable and heard a loud pop over the speakers and saw the check engine light pop on. Those are the error codes given at the top.

So looking around the forums this is what I came up:

Idle Air Control - clean it out, maybe replace it
Mass Air Flow sensor - Replace, maybe get away with cleaning it
PCV - Clean it out

Any advice before I start digging around under the hood would be greatly appreciated. Thanks for your time!

 

Welcome to FTE.

Lets think about this some more, did you have those codes stored, or a CEL Before the posted event????

If not, then the electrical pop you heard may have caused some online electrical noise thats confused the computer. So maybe try pulling the battery B- cable for 10-15 min, to wipe the codes & see how it goes, before taking things apart.

If you've had a CEL with idle overspeed & driveability problems lately, then its another matter.

The P0171 is for system adaptave fuel trim too lean bank-1 (passenger side), so this might cause one to suspect a problem with the upstream bank-1 O2 sensors PID output to the computer. If it has 75K miles or more, it belongs on your suspect list, as O2 sensors switching speed get lazy/slow with age, kinda like me LOL, so it may be change out time & I'd do both at the same time.

OR, if you've heard spark knock/engine ping lately, then maybe add dirty or faulty fuel injector to the suspect list. So maybe do a listen test on each bank-1 fuel injector, with a stethoscope, to determine if you can hear any difference in their "clicking" sound.

We need some more info to make a better guess.

 

Welcome to FTE.

Let's go back to the basics. What engine do you have?

 

Thank you, and sorry that last post was typed up in a hurry.

Engine is the 2.5L I-4, manual. 150,567miles. Had the cylinder head replaced ~10 months ago.

Now when the light first came on I noticed it idling just a little rough, barely enough to notice. It's possible it was idling like this before the light came on and I hadn't noticed it until the light told me to pay closer attention.

About 3 weeks later (present, tonight in fact) when I start the engine it revs high at first then drops down to ~900 RPM and idles rough. I'll drive home and it will drive just fine. I won't notice a thing. When I get off the freeway and come to a stop and put it in nuetral it will rev at about 1200-1400, but not roughly, just high. I'll get home, kill then engine, wait a few minutes, start it again and it will repeat. If I let the engine idle for a few minutes it will kick back up to 1300ish and just rev high, not rough. This all become typical about a week after the light came on.

A couple of times I've been able to smell it burning rich. Just what smells like unburnt fuel coming out the back. Noticed it pulling into the drive way and sitting at a light.

Listening to the engine (no stethescope) it sounds normal. No noticeable pings or clacks. The only thing that does catch my attention is what sounds like a squeeky belt but that sound is only heard from behind/under the the truck bed. No idea what that's about.

On a side note I checked the oil a week ago, it was lower than I would have guessed, filled it, and that's pretty much the end of that. No noticeable changes.

Again thanks for your help and merry Christmas.

 

Any help? Still not sure where to go from here.

 

What were the results of the things suggested above????

 

Alright, so I dug around and cleaned out the IAC and MAF sensor. Both were already spotless. No dirt came out of the IAC and the MAF looked brand spanking new as far as I could tell, well I went ahead and cleaned them out anyways. Put everything back, hooked the battery back up and started the truck. Everything ran much better, not perfect, but significantly better... for one day, then back to the original behavior, only slightly different.

Now when I put the clutch in the engine will stay revving at about 2500rpm for several seconds before dropping down to normal, OR it will drop straight to 500 rpm and usually stay there for a bit before going to normalish.

So the problem is the engine stays at ~2500rpm for several seconds before drooping OR drops to 500rpm.


Oh and the serpentine belt is looking a little cracked. That an easy one, yes? release the tensioner, pull the old belt off, put the new belt on and tighten the tensioner, let run for a min or two and make sure evertying is steal seated properly?

Thanks again for the help

 

Ok, good feedabck. Did you use a non residual spray cleaner formulated just for cleaning MAF sensors, like the CRC or Valvolene products????

Yup replacing the belt is an easy one. Relieve the belt tension, slide the old belt off the walless idler pully first, then remove.
Make sure the pulleys & surrounding area is squeeky clean before installing the new belt. When installing the new belt, route it over All of the Walled pulleys first, beginning with the crankcase pulley, then using your breaker bar in the tensioners 3/8 square drive hole, relieve belt tension enough to slip the smooth back side of the new belt onto the walless idler pully last. Double check that the belt is Centered on all of the pulleys & the molded in tensioner marks are within range, BEFORE starting the engine!!!!

On the idle anomaly, the IAC is responsible for maintaining idle speed, but if its bad, is getting a bad electrical connection, or something is sending the computer corrupted PID info, it can get confused about what to tell the IAC to do.
So maybe consider checking the TPS resistance range, paying close attention to its closed throttle value & if resistance changes smoothly from closed to wot throttle, & check the IAC's electrical input & output to the computer.

If all that is ok, maybe have a look at a sticking accelerator, throttle cable, dirty/sticking throttle plate OD, or even a randomly sticking open PCV valve.

Have you had a look at the bank-1 O2 sensors PID to the computer???

Do you still have the two trouble codes posted above???

 

Have to go to pepboys to get the codes pulled again. Have the day off tomorrow and I'll tackle all of the above then and keep you posted. Wish me luck.

As far as checking the O2 PID and electric resistance to the IAC, those are a bit beyond the tools I have at hand, so I'll stick to the simple things for moment. Unless there's an easy way to get access to something that can check that...

 

You can get a digitial multimeter from Harbor Freight for less than $5, that'll check voltages & resistance values on the TPS & IAC.

If you know someone that has a scantool that'll read & display PID's it would be easier & faster to do your trouble shooting.

 

Alright here's the update:

Replaced the IAC, 02 sensor and cleaned the MAF (with MAF cleaner) and swapped the fuel filter. Looked for vacuum leaks and found a minor leak around the front fuel injector. Replaced the O-rings around those and cleaned them up (they were kind of gunky, not sure why). Now it runs nicer, but it's still doing its thing fluxuating between 300 rpm and 3000 rpm. Even checked the spark plugs, they were fine.

It only does this when my foot isn't on the gas. Driving uphill, downhill, on the freeway or through the neighborhood it drives perfectly fine. It's only when I take my foot of the gas and let it idle on its own that acts strangely.

Improvement is that I got rid of one of the check egine codes, the only one that remains is 'P0171 System Too Lean Bank 1'.

Using the PID tool I got my hands on I ran various tests today, reseting the check engine light, rerunning tests waiting for the light to come on again and running tests to see if anything would change.

During the tests I came up with these:
P1131 Lack of HO2S11 Switches - sensor indicates lean
P1000 OBD Systems Readiness Test Not Complete
P1137 Lack of HO2S11 Switches - sensor indicates lean
P0500 Vehicle Speed Sensor A
P0304 Cylinder 4 Misfire detected (This one only came up once after I checked the spark plugs, hasn't come back since).

So I'm going to research these codes tomorrow because it's late and I'm tired, and see what's up with them then.

 

OK, good feedback, you've been busy on your trouble shoot.

The P1131 & P1137 codes are for the up & down stream O2 sensors lack of switching. As I read your above reply, you said you replaced the O2 sensor, so I assume you mean the upstream O2 sensor was replaced, so after all the work did you pull the battery B- cable to wipe the computers KAM before you reread the codes?????

Have you pulled & cleaned, or replaced the PCV valve???? With the mileage on this ride its over due for replacement & I believe Ford will replace the 4bangers PCV valve at no charge when due. Anyway if its worn & not sealing well, or gunked up & sticking open, or its rubber connecting hose is dryrotted & leaking vacuum, it can mess with fuel trim in the closed throttle position & that might be the source of your off throttle acting out.

With the scantool, set it up to monitor the upstream O2 sensor PID & see if its switching speed & voltage range looks ok.

 

Forgot about that one. We did replace th PCV since it was in bad shape too. I did not reset the KAM, but I'll get on that ASAP today.

 

After you disconnect the battery B- cable to wipe the KAM & the engine has fully cooled down, take the time to go through the cold & warm idle relearn routine here.
Ford Truck Enthusiasts Forums - View Single Post - high idle problem

 

Since my truck is a manual (and with no AC), does it still need to go through the relearn sequence?