Question about 1990 Pontiac Grand Prix

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GM 3.1 MultiPort V6 Rough Idle

I currently own a 1990 Pontiac Grand Prix. It has the 3.1 Multi-Port V6 engine non-turbo. I have owned it for about two years. The issue I am experiencing is a rough idle. The car seams to run fine until the engine warms up to operating temperature. Then when the computer takes over it idles rough. For an example, when I am at a stop light the engine will surge and sometimes it will even stall but, stalls rarely after installing Bosch Platinum Plugs instead of AC-Delco. The RPM’s go up and down. The erratic idle worsens when you use the turn signal. The car has plenty of getup and go when you are in motion but, as soon as you stop it starts its rough idle. When you first start the vehicle in the morning it runs fine until it warms up. So far I have replaced the spark plugs, spark plug wires, all three coil packs, ignition module, idle air control valve, alternator, battery, fuel pump, fuel filter and I have cleaned the intake out with a can of throttle body cleaner. I get no check engine lights or codes in the computer. The car has an electronic EGR valve that I have researched can cause similar issues if it has clogged ports or is defective. I have checked all the grounds and cannot figure out this problem! I had 92,000 miles on it when I bought it, now it has 110,000. The problem is exactly the same as it was when I bought it. Does anyone have a suggestion for me? Thank you in advance for any guidance. I have spent so much money trouble shooting and no change.

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Posted on Jan 02, 2017

taran_2005
  • 10515 Answers

SOURCE: 1991 Pontiac Firebird V6 3.1

Hi,

That code is for an IAC. Without a scan tool or something to manually drive it, you won't be able to confirm the problem is the IAC itself. Your best hope is to just take a shot and change it. See what you have after that.

Let me know,once done.

Hope i helped you.

Thanks for using ' Fixya ' and have a nice day!!

Posted on Apr 28, 2011

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