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2005 5.3 suburban idles fast

bamboni

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bamboni New Member

bamboni

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2005 suburban all of a sudden started to idle a bit fast. Not all the time but hangs up at about 1000 RPM vs. 650-750 or so that it normally runs at. I noticed it a few weeks ago. It was a very hot day, driving on interstate with AC running. Pulled off the interstate and coasting off the off ramp it appeared to not be slowing down. It wasn't idling crazy high, but enough to notice it was higher than normal. Since then it still idles fast. It never exceeds 1000 RPM and hasn't really affected driveabiity but i can tell its not quite right. It has not thrown any codes and still runs fine otherwise. I pulled the MAF and gave it a good cleaning. Also pulled the throttle body and gave it a cleaning. I ran out of cleaner so i have thought about giving it another cleaning job. I've heard about a couple issues with these trucks from intake gaskets to wiring harness on the throttle body, to MAF, to temp sensor to a whole host of things. I'm a shade tree mechanic so i don't really want to start throwing parts at it. I have heard of trying to clean the TB and MAF but then unhook battery and discharge by pushing on brake pedal. Then hook up and drive for a while until it "re-calibrates". Any thoughts on where to start? Thanks.

The Zip Senior Enthusiast

The Zip

Posted
Posted

If this was me I would start by checking the status of the alternator belt, see if it's cracked or very brittle. Followed by looking at the alternator tensioner housing to see if it is cracked. Then if both of these are in order, I would run a check of the alternator. I have an '01 5.3 and did some of the emissions control work you mentioned, but it wasn't because of erratic idle.

bamboni New Member

bamboni

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Can someone explain how a bad alternator belt could cause this? Mine looks fine, its only about 6 months old. I did have a belt tensioner chirping a few weeks ago but it seems to have stopped. It was right after I washed the truck so i thought maybe the belt was wet. Thanks.

The Zip Senior Enthusiast

The Zip

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Posted

The alternator is driven by either an accessory belt or a serpentine belt in conjunction with the crankshaft pulley, everything I mentioned above. The alternator pulley spins about three times faster than the crankshaft pulley to produce the power necessary at lower engine speeds, such as at idle. If any of those things are out of whack it can result in erratic idle. That tensioner chirping is a good sign the housing may be cracked or bearings gone bad. Take off the belt then the tensioner and check it out, you may find it's faulty. There may not be anything wrong with the items I mention, but just an easy way to start.

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