1987 Monte Carlo LS 4.3 Idle Issue

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FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
9
3
Vineland, NJ
I have a 1987 Monte Carlo LS 4.3 V6. The problem I am having is the car won't start sometimes unless I have my foot on the gas pedal for the first few seconds because its idling very low.....after its running it stays running. I noticed the idle control valve is staying shut and not opening as it should so I replaced it with a brand new unit. No difference.

Also sometimes when driving the engine randomly idles very high and that is normally how its supposed to be when you first start it, not after it has warmed up. Once you shut the car off it goes back to idling low.

Something is causing the idle control to do this....am I correct? What else can I look for? How can I correct the problem. This car has ran great for the past 6 years with regular maintenance. I'm kinda lost of where to look next.

The car runs great, perfectly smooth, no other issues. This is my wife's daily driver so she has been complaining about it so i want to try and figure it out without going to my mechanic.
 

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CaliWagon83

Royal Smart Person
Nov 12, 2017
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Orange County, CA
I can’t remember...Is that engine TBI or 4-bbl? Only reason I ask is because if it’s TBI, wouldn’t it basically be the same as the base engine in the full-size trucks? And thankfully, parts for the C/K are plentiful.
 
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Turbo Zach

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Sep 8, 2015
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I think your engine temperature sensor is bad and miss reading. I would replace that first. They are inexpensive.
 
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Turbo Zach

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Sep 8, 2015
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A while ago my mom's pickup would idle funny and after you shut it off it would not start. The temp sensor was reading it was way colder than it was and flooding the engine out with fuel. I know that is a little newer than your setup, but if the temp sensor is reading wrong it will do weird things.
 
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FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
9
3
Vineland, NJ
I replaced the temp sensor this morning. It was really stuck in the intake but I got it out. When I started the engine it high idled and slowly idled down to normal.....like it always has. I guess the old one was no good after 30 years. Thank you for all of your help.
 
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airboatgreg

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Oct 2, 2016
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Drive for a couple days and so how it goes. If all good...great..wife happy. If not post as there are a couple of other things to consider
 
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FranticItalian

Not-quite-so-new-guy
Jan 7, 2018
10
9
3
Vineland, NJ
I drove the car for a few days. The car is starting and running absolutely perfect. I guess replacing the temp sensor did the trick. Thank you guys again for the help.
 
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