Odd RPM oddity???
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Elder User
Joined: Aug 2015
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Odd RPM oddity???
Put a new Adrenaline in a week ago, so I check under the hood every few days to check for leaks etc. Yesterday it was alittle cold, so I started the truck as usual, popped the hood and went to look. Got distracted for a minute and while delayed the high idle kicked on. No problem, does that all the time. What was odd was, when I lifted the hood, the rpm start to climb slowly and stopped at about 1100. If I closed the lid, but not all the way just to the safety lock, the rpm slowly drops to about 950. Lift the hood, up it goes again. Every time. Figured, ok , hood open, more air. So checked my AFE stage 2, and its clean and no way its not flowing enough air. Restriction gauge has never moved. I can't figure out what causes this. Its not an issue. Doesn't do anying bad. BUt maybe its telling me there is some thing amiss.????????
Lead Driver
Joined: Jun 2004
Posts: 6,340
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From: Amarillo, TEXAS!
Intake or manifold air temperature sensor reading may have been right on the edge of the reading that determines what the high idle RPM should be. Hood open, it reads cooler, hood closed, a little warmer. Of course this assumes since you have an aftermarket intake, you have the sensor hanging in the open.
Disclaimer: this is speculation. I don't remember off the top of my head which sensors other than oil temp the PCM uses to determine the elevated idle speed.
Disclaimer: this is speculation. I don't remember off the top of my head which sensors other than oil temp the PCM uses to determine the elevated idle speed.
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Elder User
Joined: Aug 2015
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That's a great guess. The AFE is a huge box in place of the battery and old air box that takes the whole corner up including the battery. The sensor went in a whole in the bottom near the filter. When you close the hood, the insulation on the hood becomes the top of the box, sealing it so it takes the air in past the battery and threw the drivers fender hole. So your guess would be bang on if that's what that sensor does. Obviously with the hood open, and real cold outside it draws the cold air freely threw the open top. Closed less flow and threw the grill and fender. Wow. Good guess. I can relax now thanks.
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Elder User
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I can. I have AE on both the Infinity and my lap top. It totally makes sense to me now. Because I know if its freezing out the rpm does go up more. So lifting the hood would contribute to the temp sensor getting a lot of cold air. I had the block heater plugged in too, so hood closed it draws half the air past the warm radiator. Also probably why it didn't go to the max rpm when I first started it, it was already 100 degree. I will try the monitor thing just for the knowledge. I'll let ya all know.
Lead Driver
Joined: Jun 2007
Posts: 7,760
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From: Hampton, Maryland.
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Elder User
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He is! I didn't even have a clue that could be it.
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