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Rough Idle only when warm replaced fuel pump, Mass air flow sensor and PCV valve just got out of shop

Tiny
GARRETTRAWLINGS
  • MEMBER
  • 1999 CHEVROLET SUBURBAN
  • 7.4L
  • V8
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
1999 suburban k2500 last 4 months idles rough ONLY WHEN WARM, idles great when cold not until it warms up (drive at least 15 minutes) before it starts to happen. Just replaced Mass Air Flow Sensor, PCV Valve, and Fuel Pump by a Auto Shop they said that was all my problems, still idles rough when warm ONLY. Drops from 700 rpm to 400-500 rpm every 30 or so seconds, it is intermitten so not a miss.

Please help getting really annoyed put over $1900.00 in last 3 weeks into it, with tune up trans flush oil change radiator and everything else mentioned
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Wednesday, December 17th, 2014 AT 5:56 AM

7 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Check for a vacuum leak, may be a hose or something leaking also check to make sure intake manifold bolts are tight check the lower bolts if you can should be 30 ft. Lbs. Torque also check evap connister purge valve it may be opening up at idle and shouldn't be. It will h ave vacuum on both sides if it is. See pic it's on right side of engine.
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Wednesday, December 17th, 2014 AT 7:05 AM
Tiny
GARRETTRAWLINGS
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  • 5 POSTS
Thanks, the evap canister purge valve could very well be it I will check into it and see if I can find it lol
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Wednesday, December 17th, 2014 AT 7:12 AM
Tiny
GARRETTRAWLINGS
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  • 5 POSTS
I do know there is a line that is plastic that broke a year ago r so that runs from a canister and has been taped since? Would that be my problem
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Wednesday, December 17th, 2014 AT 7:45 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It's probably a vacuum line and yes it could do it. Get a piece of small hose at auto parts and slip over where it's broken not tape but check purge valve as well
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Wednesday, December 17th, 2014 AT 7:49 AM
Tiny
GARRETTRAWLINGS
  • MEMBER
  • 5 POSTS
Ok and is there a way to tes the purge valve I see that connection goes right to the valve itself that ataches to the motor?

Thanks
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Wednesday, December 17th, 2014 AT 7:54 AM
Tiny
GARRETTRAWLINGS
  • MEMBER
  • 5 POSTS
REPLACED THE LINE TO THE PURGE VALVE AND REPLACED THE PURGE VALVE STILL NO CHANGE?

ANY IDEAS

THANKS SO MUCH
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Wednesday, December 17th, 2014 AT 10:16 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Intermittents are hard to find and they have to do it while look ing at the car. Try cleaning the throttle plate on both sides and iac hole with choke cleaner and the other stuff I mentioned in first reply as well.
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Wednesday, December 17th, 2014 AT 12:25 PM

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