P1171 Fuel Air Metering Code in 1999 Honda Passport (Isuzu Rodeo Engine) - Diagnosis & Fix Guide

MAF cleaning doesn't confirm proper operation — does your vehicle have both a MAF and MAP sensor? Is there an EGR valve installed?

Thanks for the reply! Yes, this vehicle has both a MAP sensor and an EGR valve. The EGR is original (80k miles). Can I test it at home? My service manual states that many sensor tests are beyond DIY scope — so what about testing MAF, MAP, or EGR? Could cleaning the EGR valve eliminate the P1171 code? I’ve listed potential components but am concerned about cost. Replacing one by one isn’t practical. Any tips to narrow down the issue? Thanks for your help!

Some users have reported success cleaning the EGR valve — however, a vacuum pump is needed to test its operation, and even then, it doesn't guarantee that the valve isn’t stuck open.

I do have a vacuum pump. I’ll remove and clean the EGR valve soon. I’m trying cheaper fixes first before replacing parts — the EGR is the most expensive option, aside from the fuel pump (which I believe is new). That said, a weak fuel pump could still cause P1171 issues. Before moving to more costly repairs, I’ll perform a fuel pressure check using a $30 gauge and fitting kit.

It seems odd that an EGR valve would cost more than a fuel pump!

Original in-tank fuel pumps run $250–300. They’re notoriously difficult to install and remove. I have one general question: When the MIL comes on, does it stay lit until cleared by a scan tool? I thought that was standard — but twice I’ve seen it turn off on its own before I could clear it.

The light can go off intermittently if the issue is temporary, but the PCM should still store the fault code even if the warning light turns off.

It's common for P1171 to appear alongside P0101 (MAF) and P0137/P0157 (O2 sensor low voltage). Since I replaced the O2 sensors myself, they’re not faulty. The engine appears lean — I suspect either a weak fuel pump or failing fuel pressure regulator. But could it be that the MAF is malfunctioning? Is this causing the lean condition and triggering the O2 sensors to go into error mode? I’ve developed two scenarios: 1) A lean condition due to low fuel pressure (from faulty regulator or weak pump), causing the MAF to overcompensate, leading to multiple DTCs. 2) The MAF is sending incorrect readings, directly causing a lean mixture and triggering P1171. Which scenario seems more likely?

I’d start with the MAF sensor — that’s my top priority. Have you tried driving uphill with the MAF disconnected? That could reveal if it's sending faulty data.

I haven’t tried disconnecting the MAF yet. I wasn’t sure the car would run without it, but I’ll try that today.

The PCM should automatically use a default value when the MAF sensor is disconnected — not from the intake snorkel. If drivability improves after disconnection, it strongly suggests the MAF was sending incorrect signals.

A common issue after engine work is miswiring O2 sensors, which can cause misfires and fuel trim problems — but a faulty MAF sensor remains a likely culprit as discussed.

I replaced the MAF sensor at $100. After clearing the codes, I’ve noticed significantly better throttle response at low speeds — which was unexpected. This suggests the original MAF may have been faulty. I’ll monitor for a few days. If no further issues arise, I’ll move on to fuel pressure regulator and MAP sensor checks. Thanks for all the help!

If power returns immediately after disconnecting the MAF, you're likely on the right track.

I’ve driven about 400 miles since replacing the MAF. No codes appear. I just passed an emissions test — it passed with flying colors. The issue appears resolved. Thanks to everyone for the support!

Another satisfied customer!

This thread is quite old, but it helped me a lot. I have a 1999 Isuzu Amigo with the same symptoms and was about to spend $230 on a new fuel pump. After reading this post, I disconnected my MAP sensor — and instantly saw improvement! The car now has full power. THANK YOU!!