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1998 Acura CL with engine code P0171

First time poster, but longtime listener/viewer.

I have a 1998 Acura CL commuter car. Some time ago the engine check light came on with a code of P0171. Independent shop replaced the up and downstream O2 sensor.

Seemed to be good for a few hundred miles but the code came back. I reset the code and continued driving it without any obvious issues. Code came back again after another hundred or so miles.

Yesterday the engine stalled a couple of times when I had to stop at red lights. happened as I applied the brake and slowed to a stop. Engine kind of choked and stalled. Restarted OK, but I don’t think it’s a good idea to drive the car under those conditions.

Now I am thinking that maybe there was nothing wrong with the original O2 sensors, but they performed their functions and indicated a valid problem and the engine stalling is a result of…whatever is wrong.

Before I take the car back to my mechanic, I was hoping to get some feedback and suggestions about potential problems the car may have causing the P0171 code and what I can do, if anything. Thanks

It’s a lean mixture code, meaning there’s either too much air or too little gas inside the cylinders for some reason. Changing out the O2 sensors b/c of a p0171 diagnostic, I’d call that wishful thinking. Wishful guessing even. But if you got lucky it could have solved it, so there may be some common sense to just do it and hope it fixes the problem, not a huge expense to change out the two sensors probably. And it is possible one or both of the sensors was faulty, but there’s other problems remaining. Bottom line, problem remains unfixed … hmmm … suggest to start by making sure you have plenty of gas in the tank, then a visual inspection for air leak sources. Broken vacuum hoses, etc. After that test all the vacuum powered devices like the brake booster for diaphragm leaks. Then replace the PCV valve and inspect the PCV system hoses for broken connections, leaks. Then a quick check for exhaust system leaks. Finally, check the fuel pressure. Still not solved? Then you got some kind of engine performance problem going on, like a faulty ignition system, clogged fuel injectors, low engine compression. You could run a can of injector cleaner through the tank, replace the spark plugs, look at the engine compartment in pitch dark checking for signs of sparks flying around.

Replacing upstream and downstream sensors because you have P0171 is usually a sign that your diagnostic skills are very weak

The first thing to do is verify whether or not you actually have a lean condition

Replacing the sensors is in essence shooting the messenger

Might be something as simple as a vacuum leak, perhaps due to a rotten hose or a degraded manifold flange gasket