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1997 Pontiac Grand Prix Erratic Idle issues

Tiny
JAMESVOGEL15
  • MEMBER
  • 1997 PONTIAC GRAND PRIX
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 174,000 MILES
When started car has loping idle sounding like its miss firing. Idle rpm ranges from 500-2500. While it is like this its making sound like sucking air really hard into engine.

When driving at highway speed when foot is on petal idle stays smooth and steady, but when I take foot off to slow down for exits, will drop about 300-500 rpm and catch itself and you can feel it stagger to a stop.
My next issue is that the obd2 port is not working when plugged into any scanner. So not able to read for any codes but the light is on.

Recently replaced idle air control valve since old one was carbon clogged.
Any pointers would be greatly helpful.
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Monday, June 15th, 2009 AT 12:04 PM

5 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Hello, when you replaced the iac did you remove the throttle-body and give it a good cleaning, all the passages?


https://www.2carpros.com/forum/automotive_pictures/170934_16_pin_data_link_connector_2.jpg



you might check voltage and ground for the scanner at the datalink connector. Pin 16 is voltage, pin 4 is ground for the scanner.
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Monday, June 15th, 2009 AT 12:22 PM
Tiny
JAMESVOGEL15
  • MEMBER
  • 4 POSTS
No didnt clean out whole intake. Will try that.
What would cause the sucking noise like its trying to get more air besides the iac?
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Wednesday, June 17th, 2009 AT 12:04 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Did you get a chance to check the pins at the data link connector?
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Wednesday, June 17th, 2009 AT 12:35 PM
Tiny
JAMESVOGEL15
  • MEMBER
  • 4 POSTS
Im not getting any power to it, is there a fuse that is inline with it or something?
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Wednesday, June 17th, 2009 AT 1:32 PM
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
If there is no voltage at pin 16 of the data link connector, check cigar fuse 15 amp, also check that there is voltage to the fuse.
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Wednesday, June 17th, 2009 AT 2:50 PM

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