03-14-09, 12:17 PM
A little more help please. I have an 02 deville. Started this high idle thing about 2000 miles ago (but started out only doing it sometimes). Then recently the Check Engine Soon light came on and stays on and it is doing the high idle thing almost all the time now (but not all the time). After reading the posts I first disconnected the battery to let the system reset. No change. Then I sprayed some brake cleaner around the plenum while it was running and it slowed the engine idle. So, it looks like I've got a leaky plenam. I can fix that, however, is there anyway to do it without taking off the manifold? I haven't read of anyone else having the high idle (1500) thing. Are the two symptoms unrelated? It runs smooth when driving. Thoughts? Thank you, Scott
03-14-09, 12:59 PM
The job cannot be done without removing the fuel rail, injectors, harness, and intake manifold, as the plenum is the connector between the throttlebody and intake manifold and there is literally NO way to remove it otherwise.
It's not a bad job......a set of fuel injector seal O-rings (aftermarket) and the plenum (dealer). The intake manifold gaskets are supposed to be reusable, but you might want to replace them, too.
For the plenum try www.gmpartsdirect.com , www.gmotors.com. For the O-rings and gaskets try www.rockauto.com. If you want to get it all from one dealer, try Luke in parts at Lindsay Cadillac, over there -------->
12-18-09, 04:42 PM
I would like to thank you submariner for the great information. I just recently replaced my plenum myself, flawless job ,not too bad just the fuel rails were a pain but other than that the car is running better than ever.Ty and everyone in the forum with the info as well.
12-18-09, 06:44 PM
Tks for the feedback - did you take any pics, or do you feel like posting a "How to" in your own experience??? This group of loonies thrives on fixes and experience, so anything you can contribute is worth its weight in gold.
12-18-09, 08:29 PM
I just did 2 plenum replacements, one for my wife's 2001 Deville and the other for my son's 2001 Deville. Not to disagree, but I did it without removing the fuel rails. There is room to move the rails around to get at the intake bolts. The one bolt below the regulator was the hardest, but doable. I think it took less than an hour to do the second plenum. The job was very straightforward. There is just enough room to tip the intake up on the front of the engine and slide it out, then I rested in on the power steering reservoir. Although I had new gaskets available, I used a mirror to inspect the old ones and ran my finger over them to make sure they stayed in place. Also, I had to loosen the water pump belt guard, and also the support hook that the fuel lines bolt to, and there was enough room to slide the lines over with the manifold. Both Devilles had the 171 and 174 code, but my wifes had a racing idle, and my son's had a slow rough idle. His had the bigger split. The IAC was bad in my wife's car also, that accounts for the fast idle.
12-19-09, 02:01 PM
I've got a bunch of brand new GM factory intake manifolds with the seals/gaskets already installed. Let me know if anyone needs some. Not usually a reason to replace these, but just in case...
12-19-09, 04:44 PM
Jake - PM me. I want a spare 2002 Northstar VIN 9 intake for no good reason at all.............Jim
12-19-09, 05:21 PM
Jim - if you can round up a carb gasket kit for a 76 Delta 88 / 455 we've got a trade on our hands....parts are getting scarce for these QJets....