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Old 02-17-2007, 11:20   #1 (permalink)
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Smile Poor idle not IAC valve 1989 GM

My 1989 Marquis idle is so low it does not start properly in the cold and then once warmed up the idle seems too high for a normal idle. I need to give a little gas in the mornings for the engine to warm up and run. I have read through the forum and based on the posts removed and cleaned the IAC valve which cleared the problem for about a 1/2 day and it returned so I replaced the IAC but this did not correct the problem. I am getting code 34 call out and the EGR has been cleaned and tested. The 34 call out lists either the EGR control valve (dealer part) or solenoid valve.

I will say that the throttle body was very dirty when I cleaned it. I am also open to other suggestions.

Any help would be appreciated.....
John
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Old 02-17-2007, 12:37   #2 (permalink)
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Re: Poor idle not IAC valve 1989 GM

Update:
Replaced the EGR Sensor and this did not clear the problem.

My 1989 Marquis idle is so low it does not start properly in the cold and then once warmed up the idle seems too high for a normal idle. I need to give a little gas in the mornings for the engine to warm up and run. I have read through the forum and based on the posts removed and cleaned the IAC valve which cleared the problem for about a 1/2 day and it returned so I replaced the IAC but this did not correct the problem. I am getting code 34 call out and the EGR has been cleaned and tested. The 34 call out lists either the EGR control sensor or solenoid valve (Dealer part).


I will say that the throttle body was very dirty when I cleaned it. I am also open to other suggestions.

Any help would be appreciated.....
John
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Old 02-24-2007, 09:09   #3 (permalink)
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Re: Poor idle not IAC valve 1989 GM

Hi I have a 1989 grand Marquis Wagon 5L with the same problem very low idle in the very cold then sometime when i put it in park I get a high idle?? But I have no codes . it warmed up last week and it was fine. I'am getting bad gas miles too. I live in southern Ontario canada it was -20 C for a long time. If you fine out tell me. I have cleaned the intake did not fix it??
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Old 02-24-2007, 10:27   #4 (permalink)
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Re: Poor idle not IAC valve 1989 GM

I replaced the EGR control valve and cleaned the ports which seems to have corrected the problem. I should retest for codes but to be honest its real cold and storm is incomming so I think I will retest in a few weeks. I did not get much assistance from the forum which is too bad I found sites like this invaluable for my Saab and corvette troubleshooting and maintenance.

Note I had a call out from the OBE II port and no light on the dash indicating a problem. This tells me that without checking the codes you don't know the condition of the ignition electronics. I also noticed the some of the plastic lines are brittle I will most like redo the car's vacuum lines this spring to insure future reliability.
Best of luck

JOhn
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Old 02-26-2007, 08:25   #5 (permalink)
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Re: Poor idle not IAC valve 1989 GM

It's very important you check for trouble codes every time you have a running problem. the Check engine light only comes on if you have no/low oil pressure or the engine is overheating... it is NOT connected to the ECM !!

It is also important to understand there are 3 different ways the ECM stores and displays trouble codes. Key On Engine Off (KOEO) Key On Engine Running (KEOR) and Continuous (C)
Unless you do all 3 tests you wont know all the codes.

Vaccum leaks also have a huge impact on how these EFI motor run.
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Old 02-26-2007, 10:10   #6 (permalink)
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Re: Poor idle not IAC valve 1989 GM

Thanks I didn't realize that the check engine light was not connected to the ECM that is a very handy bit of information. I am aware of the three tests, I run all three each time just to be sure although I will admit that I skip the distributer advance portion of the engine running test.

Regarding vacuum lines is anyone bothering to replace the plastic tubes or just replacing with regular vacuum lines?
John
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Old 12-14-2007, 12:58   #7 (permalink)
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Re: Poor idle not IAC valve 1989 GM

It will be the acceleration valve in the engine. It's a tiny valve and is very dear to replace. Around about 1 thousand pounds because its a very important part of the car. I know because it happened to two of my cars - Ford transit and Saab 9000.
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Old 12-16-2007, 18:19   #8 (permalink)
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Re: Poor idle not IAC valve 1989 GM

This was last years post. ANd I have never had this problen again.
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Old 10-21-2008, 06:30   #9 (permalink)
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Re: Poor idle not IAC valve 1989 GM

What did you do to fix the problem?


I have the same problem on my 1990 Country Squire Wagon 5.0
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