WILL NOT IDLE WITH MASS AIR SENSOR AND EXHAUST HEATS UP

  • Tiny
  • FeldonKane
  • 1999 Subaru Legacy
  • 134,500 miles

99 Subaru Legacy - Without the sensor idles but does not get over 3k rpm. Ok, my 99 Subaru Legacy Brighton 2.2 will not idle with the Mass Air sensor plugged in, everything behind the cat glows orange if forced to run above 3k rpms and shoots sparks out the tailpipe, without the Mass Air sensor plugged in the car will idle when warmed up but does not get over 3k rpms and get about 12 MPGs. I have no idea what is wrong with it, have replaced the Mass Air flow sensor with 2 different ones, spark plugs, valve cover gaskets, fuel filter, cleaned fuel injector valve, and checked the cat to see if it is plugged. I am desperate as I am moving in 3 weeks. PLEASE HELP!

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Tuesday, June 19th, 2012 AT 11:00 PM

6 Replies

  • Tiny
  • ASEMaster6371
  • Expert
  • 25,556 posts

You need a back pressure test on the cat. Either that or the timing belt is bad causing retarded timing.

Roy

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Tuesday, June 19th, 2012 AT 11:02 PM
  • Tiny
  • FeldonKane
  • Member

But how would that work with it getting full RPM range with the Mass Air Sensor plugged in?

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Tuesday, June 19th, 2012 AT 11:09 PM
  • Tiny
  • ASEMaster6371
  • Expert
  • 25,556 posts

What is full rpm in your thinking?

I would start with the basics here and after that move on to other possibilities.

Roy

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Tuesday, June 19th, 2012 AT 11:14 PM
  • Tiny
  • FeldonKane
  • Member

With the sensor plugged in it will get up to around 7 to 8k depending on how close to the red line I want to push it. Sorry my Mechanic friend and I have spent close to 40 hours trying to figure this out

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Tuesday, June 19th, 2012 AT 11:17 PM
  • Tiny
  • ASEMaster6371
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  • 25,556 posts

Ok, did you do a back pressure test? Did you check the timing belt?

As far as the mass air flow, I would look at all the basics before heading in that direction.

Roy

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Tuesday, June 19th, 2012 AT 11:20 PM
  • Tiny
  • FeldonKane
  • Member

Ill be honest with you, I do not know. We may have but if we did it was a while ago as far as the back pressure test goes. I do not think we checked the timing belt though.

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Tuesday, June 19th, 2012 AT 11:25 PM

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