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Re: Fans come on RPM down 300 Posted by StoicBlue87 [Email] (#1829) [Profile/Gallery] (more from StoicBlue87) on Tue, 15 May 2018 11:39:36 In Reply to: Fans come on RPM down 300, E.j900, Tue, 15 May 2018 10:20:53 Members do not see ads below this line. - Help Keep This Site Online - Signup |
One possibility is a bad main ground cable at the battery. I've seen one Saab master tech wait beside an idling for-sale 900 and after a few minutes when the temps rose enough to kick on the radiator fans, the idle dropped quickly and then slowly resumed to normal over about five seconds.
He spun on his heel while proclaiming, "Bad ground, battery cable..."
That was a a few hundred bucks more off the price of the car.
You may be able to test this yourself by hooking up some jumper cables as a temporary ground between the battery negative post and somewhere good on the engine for ground. See if the idle drop happens when you've got an auxiliary ground like this rigged.
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