Lean trouble code question... (Not answered elseware)


>>> UPDATE <<<

I just discovered that the car is throwing both P0171 and P0174, so updated recommendations are welome :slight_smile:

No exhaust leak :slight_smile:


With both codes showing, I’m with @Tester


OK… thanks, I’ll do that :slight_smile:


I just discovered that the car is throwing both P0171 and P0174, so updated recommendations are welome


Are you certain there are no exhaust leaks? It is rather important to know especially with lean codes. At the exhaust manifold or pre and post catalytic converter are the usual places to look and be sure that there are no leaks. If you do have an unknown leak you will chase your tail pretty hard trying to solve an issue that resides with the exhaust system. So it is important to be certain. If not…then proceed down the normal troubleshooting method like you are doing now.

I really cannot over-stress the importance of the exhaust systems integrity. You will need an assistant to check it thoroughly and properly… One person under the vehicle…the other working the accelerator… Pay attention to every junction. At the cylinder head, and esp the cat area.


I’m fairly sure there are no exhaust leaks but I will have the car here shortly to begin work on it. I will first check for vacuum leaks and I will also use electrical cleaner and try to clean the MAF sensor wire.

I will also try to get some trim data for you guys.

Mom has had this car for years and I am pretty sure that the plugs and wires have never been changed. I will do that for good measure weather it could have something to do with the problem or not.


If you have an hour or so to “go to school” on (lean/rich) codes and using fuel trims to diagnose the issue then have a look at this (2 Parts) https://www.youtube.com/watch?v=5WnM_NsOtd8
Helped me out to no end with this kind of thing!


OK guys…

Found a FEW vacuum leaks and fixed them, then replaced wires and plugs. Runs really well now except that the RPM at startup still seems to run a little high on startup, for about 60 to 120 seconds. Can’t remember it taking that long to lower RPM in the past. Maybe I should check the IAC.

Outside temp is only around 65 today so the long higher RPM on startup seems a bit excessive to me.

What do you think?

Thanks to everyone for your input and advice,



The idle is supposed to be higher on cold starts. No way to tell w/out more info if it is too high or lasts too long or not. Is the high idle rpms causing you any drivability problems? My friend’s Corolla idles what seems to me to be really high at first after a cold start, for about 90 seconds to 3 minutes, but that doesn’t cause any drivability problems. If my truck idled that high I’d be getting major clunking noises when shifting from N to D, or from D to R, but no sound like that at all on that Corolla.


Does it even after it warms up. Shut it down then start it right back up.
Drivability is good as long as you wait for it to idle down. Otherwise it hard shifts into gear.



When the engine is warm, start the engine and if the idle is high, take the handle of a screwdriver and rap on the IAC valve.

If the idle speed changes or the engine stalls, replace the IAC valve.



That does seem like there’s a problem remaining. The IAC gadget is what controls the idle rpm. However if there are remaining vacuum leaks the IAC gadget may not be able to compensate. The warm idle rpm is spec’d at 760-900 rpm. Is that about what your warm idle is? The throttle body isn’t adjustable as far as I can tell. Beyond removing air leaks, the only option to change the idle rpm is to replace the IAC.


Thanks… did that. I did not reset the computer. I will do that tomorrow. That should clear it up :slight_smile:


Thanks for all the replies. No leaks now, I found all of them, repaired them and tested well afterwards.


BTW guys… the plugs were absolute toast. The electrodes were so worn down the gap on ALL plugs was like 70k.



Do you mean 0.070 inches? The specs for your car look to be 042 to 046 inches, so, yeah, 070 is not gonna help. btw, there’s some possibility running the engine with 070 plug gaps has weakened or otherwise damaged the coil packs, so keep those in mind as potential culprits should further problems develop, especially misfires.


Yes .070 - just figured everyone would know 70k.

All seems well now. The Duratec is a good engine.

The engine was designed by Porsche and purchased by Ford. Then the Ford touches was finished off by Porsche and Ford engineers together:)