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2004 Chevy Impala 3.4L SFI - P0172 Code After Fuel Pump Regulator Replacement

Model: 04 Impala Fault Code: P0172 Posted: 2009-05-02 16:57

I'm seeking advice on a recurring issue with my 2004 Chevrolet Impala 3.4L SFI engine. The vehicle currently has around 60,000 miles and has been the subject of significant repair costs over time. About two months ago, I replaced all spark plugs, ignition wires, and the fuel filter in an attempt to resolve a generic P0300 misfire code. However, after spending nearly 1.5 days at a shop, they identified that a seal on the fuel pump regulator had blown out—this was the root cause of the misfire. After replacing the fuel pump regulator, the car ran smoothly for some time. However, last night while driving, the check engine light came back on. There were no noticeable performance issues at the time, but an OBD2 scan revealed a P0170 code (Bank 1 running rich). I removed the Mass Airflow Sensor (MAF) to inspect it and found that its vent was blocked by debris inside the air filter box. I cleaned the area thoroughly and replaced the MAF sensor. Despite this, the P0172 code persisted. The engine idles and starts normally, but when I give it gas, I observe a distinct behavior: the throttle opens fully, followed by a deep rumble in the exhaust—similar to what happens when a governor is engaged. The RPMs appear to drop sharply (though I don’t have a tachometer), then the engine re-throttles back up to a stable level and repeats this cycle. Given my limited budget, I'm trying to avoid unnecessary repairs. Does anyone else experience similar symptoms with their 2004 Impala? Could it be related to the fuel system, MAF sensor, or catalytic converter? Any insights or known fixes would be greatly appreciated.

Related fault codes
P0172
Comments (3)
Anonymous 2009-05-02 18:57

How long after replacing the fuel pump regulator did the check engine light come back on?

Anonymous 2009-05-02 19:28

Approximately two months ago—replaced in January or February.

Anonymous 2009-05-04 06:48

Consider checking the catalytic converter. The 3.4L engine in these Impalas is known to develop clogged converters over time, especially after high mileage. I own a 2003 Impala with 115,000 miles and it's still running well—no issues at all. However, my 2001 Grand Am had a similar symptom: the engine would suddenly drop to around 3,500 RPM and stop accelerating, which was caused by a plugged catalytic converter. I purchased a replacement for $180 at AutoZone (a price I can afford), but a cheaper option is available—cutting out the old converter and splicing in a new one for about $65. This method reduces risk of shearing manifold studs. If possible, get a professional to inspect it or use an OBD2 scanner with real-time data to monitor actual RPMs during driving. This can help confirm whether the issue is mechanical or sensor-related. I recommend the $65 splice option for cost-conscious owners and lower risk of damage.