P0170, P0171 codes - shuggish at slow speeds. Rough idle

HARI V

MEMBER
1998 HONDA ACCORD
165,000 MILES

Hi,

I have a 98 accord, 4cl, 2.3 LX with 165,000+ miles

These are the symptoms

- Getting error code P0171 - system too lean (Bank1)
- Getting error code P0170 - Fuel trim Malfunction (Bank1)
- Idle is not smooth - slight hiccups now and then. Looks like it is going to stall but does not stall
- Does not accelerate smoothly at low speeds. Revs up, but lags when going up an incline
- Poor fuel economy - used to be around 28-29mpg. Now it is close to 20-21mpg (past 3 months)

What I've checked / replaced recently
- Took apart and cleaned fuel injectors yesterday
- Replaced throttle intake tube and cleaned throttle body - 3 months back
- Replaced EVAP Control valve, EVAP Canister to clear different CEL code - 3 months back
- Replaced Catalytic converter and O2 sensor to clear different CEL code - 3 months back
- Replaced Plugs and wires 6 months back

Now I'm stuck. Searched for these issues and some of them say to replace the fuel pressure regulator. Is that the next step? Should go to a shop and check for correct fuel pressure or vacuum leaks etc?

Thanks

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

These codes are telling us that we have too much oxygen in the exhaust, but the ECM is not able to adjust for it because the air is coming in after the intake air sensors. This is called unmetered air. Meaning the air is not measured for the ECM to match the proper amount of fuel with this air coming in.

So, we need to use this guide for checking the vacuum leak in the intake:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Clearly there are other causes of this but the most common are o2 sensor issues so if you have replaced them then we should start with this info.

I am attaching the testing below from the manual. Please run through this info and let us know what questions you have.

Thanks

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