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2000 Chevy S10 2.2L Flex-Fuel P0171 O2 Sensor Issue After E-85 Fuel Use

Model: 2000 Chevy S10 Fault Code: P0171 Posted: 2006-09-06 21:57

My 2000 Chevrolet S10 2.2L flex-fuel engine has been throwing code P0171 (System Too Lean) after I used a single tank of E-85 fuel. Previously, the vehicle had codes P0130 and P0131 related to oxygen sensor failures — these cleared after replacing the upstream O2 sensor before the catalytic converter. However, P0171 persists. I’ve ruled out major mechanical issues: the truck runs smoothly on highways but struggles in city driving with a rough idle, stalling, and sputtering during 2nd and 3rd gear at low RPMs. I tested by disconnecting sensors around the throttle body one by one; only one sensor located atop the throttle body showed a noticeable RPM difference — this led me to suspect an EGR-related issue. The EGR valve has carbon deposits on its bottom bulb, which I previously cleaned and temporarily resolved the problem. However, after a week, idle returned to around 250-2600 RPM. Switching back to the original sensor (from AutoZone) restored normal idle behavior — suggesting the replacement sensor may have been defective. I’m now considering replacing the EGR valve with a new one and installing an upgraded gasket with a screen to prevent carbon buildup on the pintle. I’ve also learned that some vehicles require a scan tool to relearn minimum EGR position after such repairs. Additionally, I suspect the Idle Air Control (IAC) or Idle Air Speed Motor (IAS) could be contributing — though I’m not certain if it’s the root cause. Any advice on diagnosing this P0171 code specifically in a 2.2L flex-fuel system after E-85 use would be greatly appreciated.

Related fault codes

P0171

Comments (7)

Anonymous 2006-09-07 05:47

Switch back to your original fuel type and monitor if the P0171 code returns or resolves — this helps determine whether E-85 is directly causing the lean condition in your 2.2L flex-fuel system.

Anonymous 2006-09-07 08:13

I switched back to regular gasoline after one tank of E-85 and have not used E-85 since — no P0171 codes or drivability issues have returned, which suggests a direct link between E-85 use and the lean condition.

Anonymous 2006-09-07 09:04

Did you clear the P0171 code using an OBD2 scanner? If so, does it return after driving or under specific conditions like idle or city driving?

Anonymous 2006-09-07 09:45

I cleared the code with my OBD2 scanner, but it returns after a few miles of driving. The truck runs fine on highways, but in city traffic, it stalls and sputters at low RPMs. When I disconnected sensors around the throttle body, only one — located atop the TB — caused a noticeable RPM change. This points to an EGR issue. The EGR valve has carbon deposits on its pintle area. I cleaned it previously, which helped temporarily. After a week, idle spiked to 2500 RPM. Switching back to the original (AutoZone) sensor fixed the idle — suggesting a defective replacement part. I plan to replace the EGR valve with a new one and install an EGR gasket with screen filter to prevent carbon buildup. Also, some vehicles require relearning of EGR position via scan tool after repair. The IAC or IAS (Idle Air Control/Speed Motor) could also be contributing to idle instability.

Anonymous 2006-09-07 15:58

A new EGR valve is often needed in cases with carbon buildup on the pintle. Consider replacing it and installing a revised gasket with a screen filter to prevent future clogging. Additionally, some vehicles require a scan tool to relearn minimum EGR position after repair. If symptoms persist, check for IAC/IAS issues — these can cause idle instability and stalling in city driving.

Anonymous 2006-09-07 16:05

IAC stands for Idle Air Control — it's a component that regulates airflow at idle to maintain stable engine RPMs. It could be the root of the idle problems described, especially if the original sensor was defective or malfunctioning.

Anonymous 2006-09-07 16:09

IAC or IAS (Idle Air Speed Motor) refers to the Idle Air Control device that manages airflow at idle. If you have a part number for your old IAC, it can help identify the correct replacement. Otherwise, ask your dealer — they’ll know the exact model and compatibility for your 2000 Chevy S10 2.2L engine.