P0171 Corrected stalling??? How

[43975]

I've been having this rough idle issue and it attempts to stall. and I've had the P0171 Cel a couipel times as well. Usually it pops on after a hard run. Cleaned the EGR multiple times and cleaned the MAF. Ran new Vac Hoses and made a vac block on the Brake booster line. All to try and fix this issue. It still existed. I usually don't leave the CEL on for longer then a few minutes.
Well this time I was too lazy to pull over and disconnect the battery so I just kept driving. At the next light I realized the rough idle and stalling had stopped. It hasn't done it at all since I've had this CEL on.

So here's my question.
What exactly does this P0171 CEL trigger mechanically and electroniclly. What ever this CEL does while it's on has fixed my idle issues. So obviously that is what my problem must be. I was under the impression that this CEL only makes the car run richer but I'm running a Split Second that will really not allow that to happen??? So what else is this CEL triggering?

 

[JDM Sam]

It's based off the fuel trims stored on the PCM. If it sees a value outside the given range limit, it throws a CEL.

 

[43975]

I know hat part. What I'm trying to find out is...Once it throws that CEL What happens? Does that CEL cause the ECU to add or remove fuel, add or remove timing, send some signal to some valve to stay open or closed...That sort of thing.

Basically the chain of events that the car goes through following that CEL being triggered

 

[BlkZoomZoom]

Why don't you try diagnosing it instead of throwing parts at it?

The car stops looking too closely at sensors basically. Depending on the circumstances it may not go into closed loop.

 

[JDM Sam]

Hello, OG.

 

[43975]

The throwing parts at it has been on the quest to figure out the issue. And I really haven't been throwing parts at it. I started by cleaning the EGR and MAF multiple times, then re did the vac lines and built the Vac block in the brake booster to eliminate any chance of a leak the BOV, WGA and Split second were all T'd off the same line. and it all all started after we installed the Split second. So I figured it was a great time to clean up the Mess of hoses and T's and do it right.

What does "hello, OG" Mean???
I'm just trying to figure out how an active CEL can fix an issue I've been trying to fix.

 

[Outlawstar98]

Check your plugs?

 

[43975]

Check I replaced them with one step colder. I even posted the Pics of the plugs in JDMSam's plug pic thread

 

[Metallic36]

Maybe the ECU tries to make up for the CEL? (dunno)

 

[43975]

That's what I'm trying to find out. What exactly does the ECU do to try and make up for the CEL. Cause what ever the ECU is doing is the answer to my problem. I think BLKzoomzoom is on to something. I don't think it stops looking at all sensors less just certain ones. if I can know which ones they are I can better diagnose this issue

 

[JDM Sam]

he's one of the old forum members on the board back when the car was new.

 

[CHIQLES]

would the air charge temperature sensor mess up the idle? if its reading hot air and the air later gets cooled isnt that going to lean out the system. Or am I misunderstanding how it works. doesnt it tell the car hey its cold out put more fuel or its hot put less fuel, Im just thinking out loud.

 

[mazdaspeedp]

maybe try the fuel filter when i replaced the wastegate and got the gasket on the exhaust manifold replaced it stopped stalling but it still has the wierd idle problem i also tryd to clean my iac and that dident fix the problem either

 

[JDM Sam]

Have you tried running the car w/o the AFC and seeing if it does or does not a MIL/CEL to come on?

 

[dandan2]

i was told that our fuel filters were built into the fuel pump! is this true?

 

[mspHtown]

i was told that our fuel filters were built into the fuel pump! is this true?

The high pressure fuel filter is built into the fuel pump housing, not the actual pump.

 

[Speed3.5]

hmm, Looks same as when it happened with mine.
I didn't bother with it since it is a O2 signal issue caused from Emanage and since you have AFC which intercepts O2 signal as well it might be the same thing as mine.
I bet it comes and goes , and usually it shows when you step on it.

When I took off Emange it never came back. Try to check the wires connecting to O2 sensor and see if you can calibrate the correct signal going to PCM.

 

[CHIQLES]

so I moved the air temp sensor to the cold pipe car seems to run smoother.I got the canada egr but that didnt realy help the bounceing idle im comeing to the conclusion that maybe my idle may be set to low and that the car keeps trying to correct itself. my idle hangs out about 450-400 maybe if it sat higher it woudnt try to over correct itself.

 

[43975]

My idle stock at 600-700
it still sits there now.
I've left the CEL on because the car has been running without any idle stalling problems while it has been on.
Very strange that a CEL would fix a problem

 

[powderider87]

do you have a air/fuel guage? my car is doing the same thing it barely idles at like 400-450 rpm. If i watch my air/fuels when i come to a stop light i watch the numbers get leaner and leaner till it goes off the chart. when that happens the idle drops and then jumps back up again, when this happens my vac also goes from 20 to 16.