System Lean


Old 01-21-06, 01:52 PM
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Join Date: Jan 2006
Posts: 1
System Lean

1999 Isuzu Rodeo; automatic;6 cylinder;SUV
Car excelerates to approx. 2000 RPM on start; then come down to zero and shuts down unless you apply gas. Runs okay until stop, when it drops off and trys to shut down again.

The fuel system is running lean. Got 3 readings on Adv.Auto Sytem: (1) PO171 - System is too lean on bank 1; (2) PO174 - System is too lean on bank2; (3) PO303 Missfire on cylinder 3.

Have replaced fuel filter and ran STP Injector cleaner through system.

Thought next step was to replace oxygen sensor(s), but discovered I needed 4 of them at $50 each. How do I test them, or am I on right track.
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Old 01-21-06, 03:30 PM
Join Date: Aug 2003
Location: Cape Cod
Posts: 4,320
Originally Posted by rtyrell
Thought next step was to replace oxygen sensor(s)
Don't shoot the messengers
They are only telling you what they are sensing

You've got other issues many miles are on the O2s?
After about 60K it's not a bad idea to replace them anyway
The quality degrades with the miles

It's more likely a fuel pressure, throttle position sensor, or MAF sensor issue
Old 01-21-06, 03:44 PM
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Join Date: Feb 2005
Posts: 435
Before replacing O2 sensor, check the intake manifold gaskets for vacum leak, they do leak due to bad gaskets and will set system lean code.

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