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1999 Chevy Tahoe 99 Tahoe rough and high idle

Tiny
WHIP
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 11,100 MILES
I have a 99 tahoe with 111,000 miles on it. It was rough idling and so I changed the #5 spark plug and that fixed it for awhile. Then it started rough idling again so I changed all the spark plugs and it stopped for about three weeks. Now it high idles between 900-1500 and when put in gear with foot on the brake, car misses. I have changed the plug wires, added HEAT and fuel injector cleaner to no avail. The car runs fine at high rpm's. I have not adjusted the idle.
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Tuesday, January 19th, 2010 AT 9:18 AM

1 Reply

Tiny
BRIAN 1
  • MECHANIC
  • 1,030 POSTS
Check for a vacuum leak around the intake manifold gasket. Very common.99 through 05 GEN III truck engines may experience any of the following:

A cold rough idle that diminishes as the engine warms up.
Possible DTCS P0171, P0174, or P0300.
Random misfires at idle. The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. Have the vehicle scanned for an codes also. Start here first.
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Tuesday, January 19th, 2010 AT 7:52 PM

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