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1.8T P0171 but normal fuel trims

Mk4 Golf

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#1 jdselby24

jdselby24

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  • Golf IV V5 2.3 10v 150PS

Posted 12 October 2020 - 04:17 PM

Hi Guys,
My AUM engined GTI has been fine since I bought it back in May but on Saturday it decided to throw me a check engine light. Happened whilst pulling into my driveway but was stopped when it came on with the engine idling.

Code scanned and comes back as a P0171 for Fuel System Bank 1 too lean. Common code on 1.8Ts as they a prone to vacuum leaks.

Fuel trims on the DTC freeze frame where -2% for STFT and 0% for LTFT. MAF Reading was 2.1g/s

Cleared the code and restarted engine to see if it would come back. Nothing.

Later that evening went driving for about an hour and a half, mixture of cruising and what in all gears, with my phone hooked up to my Bluetooth ODB reading looking at fuel trims, maf reading, Wideband O2 equivalence and boost. All looked normal. No check engine light.

Today whist sitting in traffic again the CEL comes back on, same code, idling, stopped in traffic.

DTC freeze frame was pretty much the same as the last time,

When I got home had a nose around the engine and couldn’t hear any obvious vacuum leaks.

At idle, the Wideband O2 reads around 16:1, but at 2000,3000, and 4000 rpm reads between 14.5 to 14.9.

Anyone have any idea what’s going on here?


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