High revs after start-up. - Chevrolet Forum - Chevy Enthusiasts Forums

High revs after start-up.


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Join Date: Apr 2009
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April 19th, 2009, 3:46 PM   #1  
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High idle after start-up.

Recently my '92 Lumina 3.1L has been revving somewhat high upon start-up. This occurs somewhat rarely and usually when the engine has not been ran for a day or so. It seems that this stops after a few minutes of warm-up or a couple minutes of driving.

When the engine is started up, it sometimes revs higher than the typical idle while in park and neutral. This does not occur in R, overdrive, drive, 2nd or 1st gears(while moving or not).

It is fuel injected of course...but I'm thinking it may still have some kind of electronic choke. I really have no idea what would cause this since the oldest fuel injected engine I have experience with is my '96 VW VR6. Although, my '88 Ford F150 4.9L Straight-Six(FI) almost always requires to be warmed up before it idles normally.

If this isn't normal, I'm thinking I may have a intermittent vacuum leak or a throttle body sensor that is needing to be replaced soon. BTW...There has never been an engine light on in this car.

Thanks for any advice!


Last edited by Dark Volker; April 19th, 2009 at 4:02 PM.
 
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April 19th, 2009, 4:35 PM   #2  
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Normal, every vehicle I have owned newer than 2000 has done it

 
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April 19th, 2009, 4:37 PM   #3  
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Does this usually only occur while the engine is very cold? My doesn't do this very often at all.

 
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Princeton, NC, USA

April 19th, 2009, 10:38 PM   #4  
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You have what is called a cold engine mode. If you have a tachometer, you'll see that the engine will idle anywhere between 900 and 1200 RPMs while warming up. If its idling higher than that, its not normal. It should idle right at 1050 in CEM.
Cold Engine Mode should only occur when the coolant temperature is below 100F

And I have worked with mid 60's fuel-injected cars

 
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June 4th, 2009, 2:06 PM   #5  
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It sounds to me like it is idling higher than 1200rpms when this happens. I don't have a tach though...not even one of those portable tachs that I can hook up under the hood to check rpms.

This also very rarely occurs. If the car enters CEM anytime that the coolant is below 100F, I would be getting these seemingly higher than normal idle revs a lot more often than I am.

 
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August 7th, 2009, 11:35 PM   #6  
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No worries my car does this every-time I start it up for the first start-up of the day and stops once it warms up some

 
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September 10th, 2009, 2:57 PM   #7  
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When this does happen....

It does not idle down after letting it warm up no matter how long I let it run.

The only way it idles down...at idle lol, is if I put it in gear and go somewhere. Sometimes when the idle is high like this, the car will die/stall when I put it into gear. If this happens I have to brake torque it a little when putting into gear to get moving.

 
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December 5th, 2009, 7:53 PM   #8  
CF Beginner
If my memory serves my correctly your lumina has an MAF. Most likely I'd say it could be your MAF (Mass Air Flow) sensor, which you can test by measuring resistance (ohms) with a multimeter. If you have a multimeter you can test the circuit by recording the amount of resistance (ohms) put out by the sensor at various air temps and comparing them to the factory specs. Usually that info will by in a Chilton or Haynes Manual or you can probably google it or ask your dealer. Also, its a long shot... but it could be the IAC (Idle Air Control) Motor. Try to test the motor if possible and the IAC circuit. There are circuit testers you may be able to loan from an auto parts store or buy on ebay for cheap. You may try cleaning and lubricating the throttle body and checking vacuum hoses for leaks since the fuel pressure regulator is vacuum controller (I think). It could even have something to do with the cam or crank position sensor (if you have a DIS system with no distributor) if you have a multimeter and you can test those circuits too. If nothing else, I have some of those sensors (used, but working) as spares that i will give you for free if you pay shipping. I'll do some more research and get back to you. My email is freedomfighter_87@live.com (also my MSN messenger screen name) if you want to contact me for faster response. Good luck!


Last edited by freedomfighter_87; December 5th, 2009 at 7:55 PM.
 
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February 26th, 2010, 11:31 PM   #9  
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I agree with his diagnosis.. It might be the mass air flow sensor that is having a problem or the IAC.. Have you checked on it already?


Last edited by mikeross; April 24th, 2010 at 1:46 AM.
 
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June 16th, 2010, 6:22 PM   #10  
CF Junior Member
I Have this exact same problem - mine's a 1993, 3.1 same engine - I just had the engine totally rebuilt - and it runs great, except when you first start it up in the morning... it will keep climbing rpms until it throws a SES light (OBD 1) and of course, if you just put it into gear, it fall right down to 900 or so, normal...

Replaced the Fuel Pressure regulator when they had the intake off, and it's a new EGR valve as well... IAC is original, but seems ok... MAP? I guess they are cheap enough, to just buy a new one and see... I do have a Voltmeter too... but for $30, I'd just swap it with a new one and see... could it be the TPS?

like I said, it only does this when the engine is cold, and hasn't been run - if you start it an hour later, it will be ok in Park. Does the CL light point to the MAP as well?

 
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