New to me
2003 2.3L 236K

I am working on error code P0171. What I've done so far is below the dashed line at end of this post.

Yesterday I listened for quiet vac leaks and heard two high pitched whines. One was a leak at the EGR tube connection to the IM. Despite new gasket and torquing to spec, I could stop that whine with my finger where the tube mounting plate connects to IM. A bit of high temp RTV for "caulk" and that's solved temporarily.

But then I localized another quiet high-pitched whine coming from the Idle Air Control solenoid. When I unplugged the electrical connector the noise stopped. Plugged it in and it came back.

The main reason for this post to ask how loud is too loud? In other posts people talk about IAC's howling or screeching or being "really annoying". Mine is not that. You have to listen for the high pitched whine. Is that normal, or a sign its going bad?

More details.... when engine is cold it always takes two cranks to start and usually a gas pedal pump or two. I hooked a vacuum gauge to the brake booster. When cold, and it starts, and BEFORE the IAC starts whining, I think the computer is mixing air-fuel with its default table and whether that's right or not, when it catches it idles smooth and the gauge reads 17in steady. After a moment or two, the whine from the IAC starts up. I think the O2 sensor has probably warmed enough for the computer to take over fuel mixing, and so energizes the IAC but maybe I'm making that part up? Who cares. The important thing is as soon as the IAC starts whining pressure falls way off and becomes irregular, and the idle becomes very rough.

If it weren't for you guys who might help me really understand what's happening, I'd already be on my way to the store for a new IAC to "throw that part at it too".

I have access to a "simple" code reader (Innova 3100 CanOBD2) and also a bluetooth OBDLink MX, but don't really know how to make the most of them yet.

Help please? What's going on?
THANKS!
Steve


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Done so far
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Truck came with several error codes including this last one, P0171. Partly to fix the problems throwing the other codes and partly on principle this is what I've done so far.

New air filter, plugs, wires, front O2 sensor, PCV valve and hose, and misc other vac hoses. New gaskets for TB, IAC, EGR tube, Valve cover, and Intake maniforld. Cleaned MAF, Intake manifold, and throttle body. First attempt at smoke test with homemade smoker was neg, but by ear & finger later found a small one at EGR tube mounting (Which I temporarly solved with high temp RTV "caulking"). I haven't done any testing of the fuel system. Shop mechanic once commented that fuel pump/filter "looked pretty new".

 

IAC Valve shouldn't "whine" at all.

IAC Valve has an air vent with a filter/cap on it so the valve can move freely, air can't get trapped behind the valve, if air vent is whistling/whining then valve is leaking, sucking in air from the vent hole, and thats a vacuum leak.
The valve is round with a seal around its edge, it slides inside the metal cylinder, so it needs a vent hole on the back side of the valve so it can slide back and then slide forward without an air pressure issue on the back side
No seal is perfect forever, air vent might pull some air in but wouldn't be loud at all.
If it is loud then that could also cause wandering idle, because computer is fight against vacuum pressure behind the valve so each adjustment cause a change in RPM which never settles down because vacuum changes with seal leakage

Simple test for Vacuum leak is to warm up the engine, then while it is idling unplug the IAC Valves 2 wire connector
IAC Valve will close all the way and RPMs should drop to 500 or so, engine may even stall, either is good it means no vacuum leaks

If idle doesn't drop then you have a vacuum leak

If IAC valve's vent is whining then pop off the cap and put your finger over the port, if RPMs start to drop then replace IAC Valve.

With IAC Valve still unplugged do each vacuum hose the same way, pull it off plug port with finger, if no drop then replace hose and move on to next port.
Starter with Brake booster and then PCV vacuum hoses they are most common leaks

 

Seal/cap on old one crumbled when I poked at it, and that plus the whine was enough to just get a new one on principle. No more whine at least.

Before removing the old one I did unplug the connector and RPM dropped from around 1100 to 500 just as you said. With the connector plugged in I put my thumb over the cap area but it made no difference to RPM or the whine. With the connector UN-plugged there was no whine (since it wasn't energized I guess) and again there was no change to RPM during the "thumb test".

The new one is silent at least.

Unplugging connector on the new one drops RPM from around 1100 to only around 800, by the dashboard gauge. Later I'll plug in my bluetooth scanner and check for sure.

Still throws P0171. RPM surges slightly with a rough idle and extra engine vibration at same time there's a sound... I'm not sure what knocking sounds like but am guessing the sound is knocking.

What's next? Fuel pressure test? Injector resistance?

 

P0171 reads as system Lean on Bank 1

You have a 4cyl engine so you only have 1 bank, V6 or V8 has Bank 1 and Bank 2, just FYI

System Lean does not mean engine is running Lean......................
It means computers calculations are Lean, so computer is having to add more gasoline to the engine than calculated by air weight information.

Gasoline air:fuel mix is 14.7:1 ratio, and it is a weight ratio not volume
14.7 pounds of air to 1 pound of gasoline
14.7 grams of air to 1 gram of gasoline

The computer "knows" it is running a 2.3 LITER engine, and it "knows" how much a Liter of air weighs at sea level, so based on RPM and throttle position it "knows" the weight of the air that should be coming in at any given moment, but..............................
Cold air weighs more than warm air, i.e. "hot air rises"
As you go up in elevation air gets thinner/lighter.
So Ford uses a MAF(Mass air flow) sensor to weigh the incoming air, it also has an IAT(intake air temp) sensor, to help computer to calculate the correct weight of the air.

Gasoline's weight doesn't change much when cold or warm but it does change a little, air weight changes alot.

So computer calculates air weight
Computer also "knows" fuel pressure and injector size, so it "knows" the weight of the gasoline it is adding to the engine when it opens an injector for, say 100ms(milliseconds)
It then looks at O2 voltage to see if it was lean or rich burn
If lean then computer opens injector for 102ms, adds more gasoline, then 104ms, then 106ms, and it keeps adding more gasoline until O2 reports good burn, not lean or rich

If computer has to open injectors more than 15% longer(115ms in above example), then it will set a Lean code to let the driver know there is a problem.

Same happens if Rich, computer opens injector for less time, at 85ms it would set Rich code

And these are the short term fuel trim(STFT) numbers, 15 is 15% added fuel, -15 is 15% less fuel

Unreported air, i.e. vacuum leak or leak between MAF sensor and intake are the most common causes of Lean codes.
But lower fuel pressure could also cause it, computer doesn't have a fuel pressure sensor, it assumes 60psi, in a 2003 Ranger.
But it would have to get down below 45psi or so before you would see Lean code