05 BUICK RENDEZVOUS 3.4 IDELS TO HIGH SOMETIMES TO LOW

Question edited for clarity and spelling of model name.
Question moved to model category.

Information here. You can probably just clean it.

https://www.700r4transmissionhq.com/p0405-buick-rendezvous/

Location

https://www.google.com/search?q=2002+Buick+Rendezvous+EGR+Location

....

already answered here, 26 or 29 :>D

What are the torque specs for crankshaft main and rod - Fixya

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Sept 21, 2012 - The connecting rods torque to 29 foot pounds. ... Where is the eng control module in a 2005 Buick Rendezvous ultra 3.6 eng.
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Common for head gaskets to cause this issue on this engine.

Passenger side close to the larger silver canister(dryer).

cam or crankshaft sensor, vacuum leaks.

GM Tech 2 support for on-board diagnostics on all GM systems 1992 thru 2011.The following GM vehicles utilize the CAN interface:

05 Buick Allure (3.6L)
05 Buick LaCrosse (3.6L)
05 Buick Rainier (5.3L)
04-05 Buick Rendezvous (3.6L)
04-05 Cadillac CTS (3.6L)
04-05 Cadillac SRX (3.6L / 4.6L)
04-05 Cadillac XLR (4.6L)
05 Cadillac STS (3.6L / 4.6L)
05 Chevrolet Cobalt (2.2L)
05 Chevrolet Corvette (6.0L)
05 Chevrolet Equinox (3.4L)
05 Chevrolet TrailBlazer (5.3L)
05 Chevrolet SSR (6.0L)
04 Chevrolet Malibu (Body/Chassis only)
05 Chevrolet Malibu (3.5L)
05 GMC Envoy (5.3L)
05 Pontiac G6 (3.5L)
05 Pontiac GTO (6.0L)
05 Pontiac Pursuit (2.2L)

You have a bad electrical connection. Check the wiring harness and both sides of it's connectors for corrosion and or breakage. The connector terminals will become worn and corroded and the wiring sheaths a prone to weathering and become brittle. Replace or clean as needed.

The dealer is blowing smoke up your tailpipe. I couldn't find a manual for the '04, but the '03 and '05 have identical controls for the dash lights, so it's a very good bet the the '04 is the same. Here's a link to the manual for the '05 -- you will find the dash light control on page 3-16.

http://www.extendedgmwarranty.com/owners-manual/buick/2005-Buick-Rendezvous.pdf

P.S. You might want to print the page and confront the dealer with it . . .