I used Search.. All roads point to a new thread.

So CEL P0171 = Bank 1 System Too Lean

My issues:

Car idles horribly at different times. When I cold start it - it's fine with idle.

When the engine is warmed, idle is pretty rough.

Coils / MAF / Plugs are fine.

So..

Fuel pump and compression are a possible issue. Basically, I can only get the car checked on Saturday.

 

 

http://lmgtfy.com/?q=site%3ARx8club.com+p0171

Took a few seconds of reading to see that it's a vacuum line problem.

 

As stated. Search was used. All threads on the topic point to no correct end. Forgot to state I had the system vac'd. Even used Brake fluid on all area's where air can be drawn in to check for an RPM rise. Nada.

 

You still have a vacuum leak. The code and symptoms point to it.

I had a vacuum leak for over a year. A very slight one, and only affecting the rear rotor (rear intake tract seal from UIM to LIM), so I didn't have any manifested problems, and using vacuum leak test methods kept showing it to be solid. But it showed on the logged engine data, and once that was pointed out to me, I pulled apart the UIM and immediately found it.


With any vacuum leak, essentially the engine is pulling in air that is not passing the MAF, causing the MAF information to be inaccurate. Depending on how big that leak is, and where it's located, it could manifest in several different ways. A small vacuum leak makes a bigger difference at idle than it does higher than idle, because of the % variance that the difference in airflow is. For example, your engine should be pulling about 5.5 g/s of air at warm idle. If you have a 1 g/s vacuum leak, you have a 20% variance. Bring the RPMs to 1,300rpm for a cold idle, and you are closer to a 10 g/s or so, which is only a 10% variance. Difference vacuum leaks could change the relationship as well, so don't take my numbers as hard-fact.

In your case, the cold idle is "overwhelming" the variance, but at warm idle, it's significant enough to be noticeable.

 

I smoked the system already, apart from going through every area of potential vacuum. Any other way to diagnose this.

I agree on the Code pointing to too much oxygen - however. I've checked it professionally already, though there is room for human error. This wasn't done on a singular occasion.

Seems like a stupid, menial issue - I just can't pinpoint it.

 

None of those methods found mine either, but the log data clearly showed that I had it, and when I pulled data after fixing what I found, the data showed it was gone.

I would be inclined to say that smoking the system may not have found it because under vacuum, it's pulling something flexible into the intake tract, making the leak, where pressurizing the system with smoke is "sealing" it even better.

I would recommend taking an afternoon and pulling off your UIM (accordion, then air box, then disconnect all hoses and wires from the UIM, unbolt 7(?) bolts between UIM and LIM, 2 bolts under the UIM, lift off)

Once off, inspect all gaskets between the UIM and LIM, look for any crimping, pinching, deformation, look for any carbon blowby (should be clean metal outside the gaskets on the face of the surface). It should be fairly easy to pick up on what isn't right. If everything looks normal start next with the hoses and nose nipples, look for cracks.

 

I'll do it Saturday..

In the meantime. A little O2 never hurt anyone.

 

I don't use a smoke machine, too high of failure rate, my "fog machine" now sits on the shelf under a roll of duct tape, and an 80's dwell tachometer.

But i'm not going to tell you what doesn't work without giving you something that does.

go to home depot/lowes/ace and buy 3.5 inch PVC cap, if you want to prep for future cars you could do this to go ahead and get a 1.5" 2" 2.5" and a 3".

you want to get some sort of compressed air pressure regulator, with a gauge. The one i have has about a quarter of a turn to full open, but it was also rather cheap. you'll also need a air hose connector, and a tap.

Drill and tap the pvc caps and thread in your regulator. put this in place of the MAF housing, and apply 5-10 pounds of pressure, then spray all over with some soap and water, make it really "sudsy." i've had a few dipstickd blow out and hit the shop wall so be really careful about how much pressure you apply, it could easily damage something.

where ever the foam/bubbles are, that's your vacuum leak. THAT's how we professionals do it.

 

lastphase:
Curious, what are your feelings about a leak that forms a "1-way valve", where pressurizing from the inside seals it shut, but creating a vacuum inside opens it up. I can mentally see several ways this could happen, like a gasket deforming slightly, and the vacuum pulls it in toward the inside, opening up a gap, but pressurizing it forces it back to where it should be.

 

It's the pressure tests companion in finding vac leaks. Starter fluid At idle.
The vacuum inside of the intake will be at it's greatest during decell and idle. i find that brake cleaner's combustibility is insufficient, and so I only use starter fluid.

and the check valve effects does happen more often then you think...

If one doesn't find it, the other one will. At least, I've never experienced one that went beyond that.

The first step is always a thorough visual(no touching anything, you don't wanna inadvertently find/fix it with a customer standing next to you).

 

Just an update..

The entire system was checked for a leak.. Nothing found. My MAF had a screw that was semi loose - but not enough to cause a leak. I also don't think a loose MAF would cause this idle - it was still secure.

Also decarbonized my engine and changed my plugs for the hell of it. Coils are fine.

Still bad idle. **** me. CEL cleared itself by the way.

 

When you cleaned the MAF, did you get the spray up inside?

The bulb on the Maf is just an air temp sensor, the actual MAF wires being up in the body.

K&N air filter? That would also do it....

 

Yeah, I didn't even touch the bulb - heard they break quite easily. If I confused you on the screw - its the two screws that actually hold the MAF down into the intake (One was loose).

And I'm using the factory intake. Was debating an AEM for looks and space reduction, but that's only after I solve this -+(leak)

 

I think Stealth was asking if you sprayed the actual sensor (MAF), or did you just spray the bulb (IAT sensor)

 

The actual MAF.

Just an update...

Things done so far..

Replaced plugs
Decarb of engine
MAF cleaned
Coils - Checked, less than 5k on them
No leak in UIM (Did not take apart LIM - Entire system was checked from the outside though, used above method ^)
No loose/disconnected hoses
Catalytic Converter Replaced (Under Warranty)

Next step?

 

engine hot = rough idle?
engine cold = smooth idle?

What can cause a rough idle with the engine fully warm...? (think internally. exhaust, etc)

 

Just read about the neutral switch possibly being bad. Doesn't have a distinction on hot or cold. Also have read about the engine knock sensor - however my mounts are fine.

****.

I'm seriously stumped and at this point just looking for things to check.

 

Cat
compression
eccentric shaft position sensor
...

 

^ Forgot to note my cat was replaced.
After Decarb was done, compression was checked.
Also with the plugs, esps is right there so it was checked.

 

after checking/cleaning the esps, did you reset the NVRAM (20 brake pedal stomp)?

 

Certainly did sir.

 

 

I have this CEL also, but my idle is fine, the vehicle runs great. Only thing i notice is a slight whistling sound on low load partial throttle.

 

Just curious how you checked your coils because there really is only one good way to check them and its not the service manual procedure

https://www.rx8club.com/series-i-do-yourself-forum-73/diy-testing-all-rx-8-coils-gm-ls2-yukon-coils-sparkplug-wires-222641/

A primary factor in idle quality is the trailing coil function. Regardless of how new they are you should doublecheck the coil and sparkwire under load per the diy thread link above.