Question about 1999 Cadillac DeVille
The IAC or idle air control valve is mounted in the throttle body and uses an air passage that opens or closes to increase idle speed where as an idle motor usually pushes against the throttle plate to increase idle speed most idle motors (stepper motors) where phased out and was never used on port fuel injected engines chances are you have an IAC valve
Posted on Dec 11, 2012
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Posted on Jan 02, 2017
The normal coolant temp should be around 200-215 degrees.
The cooling fans will come on at around 225-228 degrees.
The most common overheating problem with the Northstar engine is a blocked purge line(small hose).The purge line is designed to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank (not the cap) ,this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.
If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.
The hose goes in to the engine to a crossover and comes out the other side close to the thermostat housing,the blockage may be there.
Posted on May 22, 2010
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Posted on Feb 28, 2010
SOURCE: 99 cadillac de ville
the coolant temp sensor is at the rear of the engine and is a "bad word" to get to. the 3 relays are at the bottom,under the fans. if you remove the driver side fan out of the way( 2 10mm bolts holding the fan) you should have good access to them. they do have locks on them and may be tricky to unplug. there is a 7/16 nut holding the relay plate down. remove and it should be easy to remove them.
Posted on Jul 09, 2008
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Posted on Jan 20, 2011
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