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P1131 "too lean" code, where to start looking for vac leaks?


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getting P1131 code on 1999 Merc 3.0 Vulcan with about 100,000 miles that I've had for couple years and about 12,000 miles buts mostly been sitting for last year but moved every couple weeks.

Unlike the guy in video in first section in link, I've only got the one Code.  I cleared Codes once and it came back on after about 5 miles of driving.   Sable HAS had a sort of uneven....not quite missing and not really "hunting" but sort of pulsing but pretty mild for some time.  Non-car type people say they don't notice anything.  Sable just passed SMOG in CA a month ago and less than 10 miles before Code came on, so I'm sorta wondering if the Smog Guy moving stuff around for inspection didn't cause some old Vac Tube to start leaking or something.

I guess I'm hoping its not a Manifold leak.

https://www.engine-codes.com/p1131_ford.htmlP1131 FORD code possible causes

 
  • Faulty Upstream Oxygen Sensor Bank 1
  • Fuel pressure high or low
  • MAF sensor dirty/defective
  • Vacuum leak on engine
  • Leaking fuel injector or fuel pressure regulator
  • Faulty Powertrain Control Module (PCM)

 

 

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Definitely check the air intake hose between the air cleaner box and throttle body for any cracks or loose seals.

Also worth checking the crankcase breather where it goes into the intake, sometimes the boots on the ends get crumbly and start sucking air. Inspect vacuum lines while you're there as well.

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  • 2 weeks later...

thanks, everything LOOKS pretty good but will check again.  Are all Vac tubes easy or are some hidden on the back side?   I tried spraying some carb cleaner around to see if it would change RPMs but didn't.

It JUST passed Smog so I guess I'm G2G for two years and its a disposable extra car, but maybe I'll take to Smog guy AGAIN to diagnose or at least figure out if leaving unaddressed will kill the Cat or burn valves or something.

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PS-  If I take it to some mechanic how can I know the code and issue was really fixed because I cleared codes once and it takes a few miles of driving for it to come back on.  Will OBD be able to say "Yeah, its now fixed" and turn off code on its own or does code need to be turned off then wait to see it it comes back?

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