P1171 Fuel Air Metering code for Isuzu Rodeo, Honda Passport

Does anyone have experience or ideas on troubleshooting an Isuzu P1171 DTC? The vehicle is a 1999 Honda Passport, but it has the Isuzu 3.2L V6 engine and is the same as the Isuzu Rodeo. The car runs and drives great but will return a P1171 “Fuel Air Metering” code when I try to drive on hilly roads. If I pay close attention to the car, it feels a little sluggish sometimes then bingo the light comes on and the same code shows up every time. I also get a P0137 and P0157 low voltage code for the 2 downstream O2 sensors, so I replaced them even though those codes are probably secondary and not the real problem. Other than a slight sluggish feeling sometimes and the P1171 code, the car runs great. If I don’t drive up any big hills and do mostly flat driving, the code light never comes on, so the error may or may not cause the car to fail an emission test.

Things I have done to try and fix the problem are: replace downstream O2 sensors, replace air filter, replace fuel filter, replaced some questionable looking vacuum lines, added 2 cans of fuel system cleaner and ran it through, cleaned the MAF Sensor, cleaned the accessible parts of the throttle body (did not remove it), and replaced the spark plugs. I’m pretty sure the previous owner replaced the in-tank fuel pump. It’s a noisy pump. I’ve replaced several in-tank pumps on newer model cars and have noticed that sometimes the aftermarket pumps work fine but are noisy from outside the vehicle. For now, I’m eliminating the fuel pump as a potential problem.

The 3 things I’m focused on now are the MAF Sensor, the MAP Sensor and the fuel pressure regulator. I’d hate to spend a bunch of money on each part by way of process of elimination, but I’ll do whatever it takes to fix the P1171 error. Anybody have any ideas? Thanks in advance for your help!! Jim

cleanning the MAF doesn't verify that is in fact reading properly! Is it equipped with a map sensor as well as the MAF? Is it equipped with an EGr valve?

Hi, Thanks for the response. Yes, the car does have an EGR valve and a MAP sensor. It EGR valve looks original to the car (has 80,000 miles). Is there a way to test the EGR valve? My service manual says "...is beyond the scope of the home mechanic, etc" in regards to the testing of many sensors, so it doesn't tell me much about testing the MAF, MAP or EGR items. Is the EGR valve something that can be removed and cleaned effectively and possibly eliminate the 1171 code? I've got a list of specific sensors and other things that could potentially be the problem. Replacing them one by one is not practicle due to the cost of each separate item. I'm trying to pinpoint the specific problem. I appreciate your input.

some people have success cleaning the egr! You need a vaccum pump to test that it will open but it doesn't prove that it isn't stuck open!

I have a vacuum pump. I'll take the valve off and give it a thorough cleaning and see if it makes a difference. I'm trying the free and less expensive things first, then I guess I'll start replacing parts cheapest to most expensive until I solve the problem. The EGR valve is the most expensive part of the bunch, excluding the fuel pump which I believe to be new. That doesn't mean it's not weak though, and that is something that can result in a 1171 code, or so I've read. I need to do a fuel pressure check before going too much farther into it. I'm pretty sure I can buy a gauge and fitting set for around $30.

seems odd that an egr would be more expensive then a fuel pump!

Yeah, the OEM pump assy runs about $250-300 and is the in-tank design. Loads of fun to remove.

I have one general question: When a fault occurs and the MIL comes on, should it stay on until it is cleared by a scan tool? That's the way I thought it worked, but twice I have seen the MIL come on and then go off by itself before I had a chance to clear it.

it can clear by itself if it's an intermittent problem but the pcm should store the fault even if the light goes out!

Sometimes when I drive on hilly roads and I can make the MIL come on, the DTC set includes P0101 for the MAF. It always includes the P0137 and P0157 low voltage O2 sensor codes, and the P1171 is the final (and pending) code. I know the O2 sensors are brand new because I replaced them myself, so it can't be faulty O2 sensors. I've been trying to figure out why the engine is running lean (P1171), thinking that the problem is a weak fuel pump or (going) bad fuel pressure regulator. Is it possible I'm focusing too much thought on the pending lean condition P1171 code and should instead try to resolve the P0101 code first?

I've come up with two different scenarios at this point:

1) The engine is running lean due to a faulty fuel pressure regulator or a weak fuel pump, and that is causing the MAF to overcompensate which results in a set of DTC's.

2) The MAF is malfunctioning and causing a lean condition that then trips off the O2 sensors and causes the P1171 code to show up.

Which is the better sounding scenario?

the MAf would be the first scenario I'd check out! Did you try driving on the hills with the MAF disconnectted?

I haven't tried disconnecting it and then driving it. I wasn't sure the car would run with it disconnected, but I will try that today.

the pcm should substitute a known value as a limp in with the MAf connector disconnectted! Not the snorkel! If it seems to have more power or better drivability with it disconnectted then it's possible it's sending a incorrect signal!

A pretty common problem is after major engine work is done the O2 sensors can be plugged in wrong and cause multiple misfires, fuel trim problems and MIL illumination. But it could be the MAF like you've been discussing.

I decided to go ahead and replace the MAF Sensor. At a cost of $100, it's not that bad. I cleared the DTC's, and so far so good. I've noticed a definite difference in throttle response at low speeds after having replaced the sensor. Is that common? I wasn't expecting that, so maybe it was a bad MAF after all. Time will tell. I'll give it few days and see what happens. If this doesn't fix it, I'll focus on the fuel pressure regualtor, fuel pump and maybe the MAP sensor. I appreciate all the help I've gotten from you guys!! Thanks!

if the power seems to be back right away then you're probably on the right track!