Hey guys,
I'm new here so forgive me if I've missed something obvious. I have googled this and I haven't found any answers (yet) that apply or that I haven't tried already.
First, some history. My girlfriend has a 2002 Pontiac Grand Prix GT, completely stock 3800 series engine, automatic transmission. It's got almost 130k miles on it and over the past few years we've owned it, we've put a lot of work into it. Recently we broke down; left a restaurant and couldn't start the car. It would crank and crank but would only run for a second and then die. We were desperate and cranked it to the point of it starting to smell like rotten eggs due to rich fuel mixture.
After some googling on my phone, I found a website where someone suggested pulling the connector off the mass airflow sensor and trying to drive without it connected. I did this a we were able to start and drive the car to the nearest auto parts store! The check engine light triggered but we were no longer stranded. I read the code later and it was the code for having the MAF circuit open; I don't recall the exact number. I changed the MAF in the parking lot and afterward we were able to start the car and it would stay running this time instead of dying right away. The CEL went away (but the code was still in the computer) The idle was now rough, whereas before the breakdown there were no problems with the idle, but other than that, we were relieved to be able to drive the car around reliably. It seemed a little odd that the idle was rough but it drove fine, didn't hesitate, had plenty of power. I chalked the rough idle up to the computer needing to re-learn after having the MAF replaced, and I figured it would go away after enough time / miles had gone by.
About a week later we took the car in to get it inspected. We live in New Hampshire and we have emissions tests. At the same time, we had the air conditioning condenser and dryer replaced, since the condenser had developed a leak. The technician opened the coolant lines etc to get radiator out of the way to do the A/C work. When the work was completed, the tech found we had a new code: P0171 He performed a re-learn using his scan tool but the code came back. He replaced the upstream oxygen sensor and put a new fuel filter in; no change. He measured the battery voltage and found that one of the terminals was green and the battery was only measuring 10 volts... he cleaned the terminal and we got a replacement battery but the P0171 code has come back... that's a re-cap of the last two weeks. We just can't get this code to go away.
Interestingly enough, the idle had gotten worse at this point, and a couple times the car had stalled and had to be re-started; but not like the original MAF issue (where the car was absolutely not staying running when the MAF was bad). Under load (A/C compressor on; brake depressed and in-gear, drive or reverse) the idle cleans up. In park or neutral, the idle was kind of rough and the engine would vibrate. The replacement battery seemed to help the idle, it's still not perfect, but a lot better. However, the P0171 remains.
I'm at a loss. I feel like we have checked almost EVERYTHING and we still can't get the P0171 to go away. At this point we can't get an inspection sticker because of this problem and we've been waiting more than two weeks to get the computer to return clean codes so we can get an inspection sticker.
Here's a list of things that have been replaced that might be relevant to the P0171. I am CONSTANTLY fighting CELs on this vehicle. I am open to the possibility that some of these "new" parts might be bad but I just don't know where to start (or re-start) and I would be very grateful for some guidance.
- In the last year: replaced the fuel sender unit, gas gauge didn't work, also replaced the fuel pump at the same time
- In the last year: mufflers replaced due to rust
- In the last year: secondary air injection pump replaced due to code
- In the last year: air filter replaced for routine maintenance
- In the last 8 months: cat-back exhaust (not incl. cat) replaced due to rust
- In the last 8 months: throttle body cleaned due to sticky throttle; IAC pin is clean
- In the last 8 months: thermostat replaced due to poor heat
- In the last 8 months: coolant temperature sensor replaced, also related to poor heat, temperature gauge didn't seem to read correctly even after thermostat replacement, gas milage improved after replacement
- In the last 6 months: downstream O2 sensor was replaced (code for downstream O2 heater circuit, tested bad with a multimeter and replaced, code went away)
- In the last 6 months: catalytic converter replaced (code for catalyst efficiency; checked for and repaired exhaust leaks but didn't resolve; replaced catalytic converter and code went away)
- In the last month: MAF replaced due to apparent malfunction
- In the last week: Checked PCV valve, checked MAP sensor seals
- In the last week: smoke tested for vacuum leaks, none found
- Checked the vacuum line on the fuel pressure regulator for fuel seepage; none found
- In the last week: upstream O2 sensor replaced in an attempt to fix P0171
- In the last week: fuel filter replaced in an attempt to fix P0171 (and it was due for replacement)
- In the last week: battery replaced when it was discovered the original was only 10V, probably dead cell
- In the last week: the computer has been reset multiple times; codes cleared and a "re-learn" performed by the tech using his scan tool
The only thing I can think of to have them do next is a fuel pressure test? Maybe we have a bad fuel filter or the less-than-1-year-old fuel pump is weak? Fuel pressure regulator bad? I think the only sensor we haven't replaced is the MAP sensor, and perhaps the intake air temperature sensor. I read that the P0171 is triggered when there is a 20% discrepancy in compensating for the air-fuel ratio, that seems like a lot, so how is this cause and solution not obvious??
I appreciate any input anyone can provide. Thanks in advance.
