Some history:

2001 Impala with 3.8 about 100k miles. When it got in the single digits this winter, car would crank and crank with no spark. Changed Ignition Module, problem evidently solved, it starts with no problems now.

While checking things over, I found some issues and fixed/replaced the following:

Ignition Wires
Spark Plugs (iridium)
Coil (was a little weak, replaced)
Fuel Pressure Regulator
Radiator (plastic hairline crack)
Thermostat (old one stuck open)
EGR (cleaned, wasn't very dirty)
MAF (cleaned with electronics spray)
Vacuum Hoses and lines (replaced just about all, OEM stuff was hard as a rock)
Air Filter
Ran a can of GM top end cleaner through it.

Car has a bit of a stuble at idle (very small , but it normally idles rock solid.)
Checked for leaks, and as far as I can tell there are none.

I'm stumped, going to check fuel pressure, but it doesn't seem like a FP problem.
I am going to see if a friend of mine who has a garage will let me use his smoke machine this weekend just in case I've missed a small leak.

I also found that the small tab which holds the o-ring on the dipstick tube has separated from the top, but it still seems to seal fine.

Any BTDT'* on this? P0171 Bank 1 Lean is the only code I'm getting.

I just had this problem. Check out these areas

• The EGR tube for cracks
• Spray Carb cleaner at the base of the fuel injectors to see if it stumbles. That indicates poor fitting injector O-rings
• Fuel Filter

Also check around the LIM gaskets. Any leaks can cause that code.

Thanks, I checked for leaks with carb cleaner, brake cleaner and even old school propane and found nothing. I got a new fuel filter with the rest of the stuff, I guess it wouldn't hurt to actually install it.

Tomorrow I'll hopefully be able to borrow the smoke machine and see if there are leaks which have eluded me so far.

Which vacuum leak is more common on these, the upper or lower manifold? Any place in particular they tend to leak more often?

I'll post after the test, crossing my fingers, this one'* kickin my arse so far.

check all the hoses.

Neither manifold are common for vacuum leaks. They are common for the gaskets breaking down and looking horrible, maybe a coolant leak or oil puddling...but not vacuum.

A 13mm bolt and 13mm nut will have that EGR to LIM tube off. It'll most likely have a crack in it where the piece holds it to the LIM. It'* very common.

If that doesn't work, search my user name and P0171. I own stock in this code.

Smoke test showed nothing. The only leak I found was at the dipstick, and it was minor. The rest of the system is tight as a drum, so that pretty much rules out false air.

Put the gas filter in, didn't expect it to do anything and it didn't disappoint.

Checked the EGR plumbing, looked new, no leaks or splits that I could find. Wouldn't it have made some noise or had trace marks if it were leaking? Moot point anyway, the pipes were fine.

Tomorrow I'm getting the MAF sensor, I cleaned the one in the car, but who knows? It'* not that cheap, and I can return it if I don't muck it up. Hopefully I'll have good news tomorrow.

Going to check the fuel pressure too, but it seems fine, the thing will go to redline at over 100MPH, if I had fuel delivery problems I figure they'd have manifested themselves.

Today was the first time I drove it cold (it'* the wife'* car), and when it'* cold it stumbles and feels like it'* cutting out, died at a set of lights or two but has little to no driveability problems once warm.

P0171 still kicking my arse.

Dude, fighting the 0171 myself. It truly does SUCK. I am having drivability errors though, so maybe mine will be easier to figure out. Been almost 2 months fighting it for me.

Have you checked your PCV valve? I seem to remember a few people getting this code form bad battery connections. Another area that causes this code is the EVAP system. You can cap it off and see if the code clears up. If so, you need to start hunting those lines.

I installed a brand new MAF sensor. Car still missed, stumbled cold, RPM'* were oscillating about 100 RPM, I didn't even wait for it to warm up, parts runner came by to bring some more stuff, so I returned the new MAF sensor and reinstalled the old one.. I had reset the MIL light, I didn't wait for the code to pop with the new MAF, car was behaving the same.

(Cue spooky music here)

I drove the car all day, at least 10 on/off cycles. In town and highway speeds, and....NO MIL light, NO DTM'* stored either???

I'm lost for an explanation at this point. I did nothing, absolutely NOTHING except swap in a good MAF, run the car for about 3 minutes, remove it and put in the old one.

Previous to this, the simple act of holding the RPM'* at 2-3k RPM would set the "lean bank 1" DTM rather quickly.

The car still is a bit hard to start, and stumbles and misses once in a while, but, NO check engine light and no codes, pending or MIL.

P0171 no longer kicking my arse, but the mystery continues. I told the wife to take the car tomorrow, so she'll be reporting back on how it goes. It seems I got my wish but it'll probably be a bigger PITA to figure out what'* going on with the intermittent stumble and miss now that the car is code free.

I guess it'* true, there are two tragedies, one is not getting what you want, the other is getting what you want.