gondwana1

Hi,
I noticed some driveability problems on my accord (4-cylinders - Automatic Transmission).
1. When I get to a streetlight or have to stop or slow down to a near stop, the engine goes off and I have to restart the car.
2. When i start the car and engage drive or reverse, the engine goes off when i step on the accelerator.
3. When I rev the car on park/neutral all is normal but the engine goes off when I remove my foot from the accelerator

This has been happening for a while now and the CEL comes up with P0420-Catalyst System Efficiency Below Threshold (Bank 1). I kept on clearing the code.
A couple of days ago, the check engine light came ON. I did a scan and came up with the code P0171-System Too Lean (Bank 1). There is also a pending code P0420-Catalyst System Efficiency Below Threshold (Bank 1).
I did a real time monitoring with my scan tool and observed that the Short term fuel trim varies from 20-45%. The Long Term Fuel Trim is also greater than 20% which explains the P0171 code. Also, this lean condition increases as the engine speed (RPM) drops.
I have done some research on P0171 and any of the following can trigger the code: bad injector, vacuum leaks, dirty fuel filter, weak fuel pump, dirty MAF sensor, bad fuel pressure regulator, bad fuel feed line, faulty O2 sensor etc.
I am hoping that someone would be able to point me in the right direction using the symptoms I have noticed in the driveability particularly the engine going off.

Any help/suggestions will be greatly appreciated.
Thank you in advance.

justinsbg

Have you checked for any foreign debris in the Mass Air Flow sensor? If not, I would start there before I got to heavy into trouble shooting. If you see some leaves or anything like that I would vacuum it out. Don't use compressed air to clean the intake and sensor but vacuum it out. Those are some pretty high fuel trims. I have had some trouble with the air/fuel sensors on these model Accords but never do they stall completely. Usually the symptoms of the air/fuel sensor problems are the car surges for about 3 seconds and then drives normally. Check the MAF and get back to me.

Kdrane243

@ Justinsbg. I just had a similar problem, and your post pointed me in the right direction. I found that I had accidentally knocked out the device that is plugged into the air intake tube while replacing the VTEC oil pressure sensor. fuel trim went from 49% down to 1.6%. Thank you.

gondwana1

Thanks for the replies.
I discovered that the air flow tube between the MAF sensor and the throttle position sensor was torn and unmetered air was entering from this leak. I replaced this and the P0171 code has not come since then. . The engine has stopped going off at low speeds. I am still having the P0420 code though