It's the little things that bug me...

flyboyron · February 14, 2013

I have an 09 ext. cab with a 5.3L and a 4 speed.

After I first got it I noticed that when the truck is idling that about every 10 seconds or so it will shake for a second and then get smooth. It will continue to do this. I asked the service writer when I took it in for an oil change the first time and they said it was normal. Well, I know that GM would not make a V-8 that was not smooth, for God's sake, my Honda Civic with a 4 cylinder idled so smooth that you couldn't tell it was running. Why they would purposely make an engine not smooth is beyond me.

Now sometimes not all the time, but sometimes, when I start the truck, the engine revs up to 1,500 rpms. Now why does it have to rev up that high? The engine isn't cold. Is that so I can hear it and to let me know it is running?

Driving down the road, if I take my foot of the gas pedal, (my mom called it the foot feed) LOL, the truck will coast quite a while. It seems the engine has no compression to slow it down. Going down a hill on the freeway the truck will actually gain speed. So that is good, it saves me gas mileage.

Then sometimes, I take my foot of the pedal, and I can feel the truck slow down. It is almost like the brakes are on. It is really weird why it does this sometimes and not all the time.

Then a couple of months ago I get this letter about a service bulletin I think it is on the throttle position sensor?

Then that makes me worried.

Could all of these things I noticed be related?

MikeNH · February 14, 2013

My 2011 shakes sometimes, never really concerned me. Don't really know what to tell ya on that.

The high rev thing has to be related to some engine coolant temp threshold- I know exactly what you're talking about. Every vehicle I've ever driven idles high for a bit when cold (note that "cold" might not actually be cold- just a temp below what the ECM thinks is cold). Likely something to do with emissions- maybe that short blast of high idle gets the cats warmed up faster? All I know is with the Corsa/dB exhaust that high idle start sounds beastly.

The trans acts funny sometimes. Every now and then it will drop a gear to slow you and sometimes it won't. You want some good times, turn on tow/haul and try the grade braking feature. Just make sure you got that seatbelt on.

I'm sure this isn't exactly what you were looking for answer-wise but this is what I've seen. 2011 Silverado, 45k miles or so.

GMCustomerService · February 15, 2013

flyboyron,

Has your concern been resolved? Have you had a chance to mention this to your local dealer? Feel free to contact me privately if you need additional assistance. Thank you.

Tricia, GM Customer Service.

Bad Bowtie2 · February 15, 2013

I guess in 2009, when the 6-spd 1st came out in the 1/2 tons, not ALL GM 5.3L trucks had them?? Maybe it was an extended cab vs. crew cab thing??

I thought just the 4.8L trucks still had the 4-spd in 2009 & up.

-Just a side note that I was surprised to read that your 2009 Ext'd cab 5.3L had a 4-spd auto.

My 2004 GMC Sierra VHO had the H.O. 6.0L & it had the "rough idle" condition at times. I had always read that guys with tuners & re-programmed PCM's turned up the engine idle just 200-250 rpm & eliminated this problem.

Wires · February 17, 2013

OP, all of those sound normal:

1) These engines idle VERY slow and stupid lean for emissions. They typically idle down, shutter, and idle back up. I think mine idles around 600 RPM. At such low RPM, recover time for the lean idle is longer, hence the shutter. 4 cylinder engines idle higher, so you don't get that same issue.

2) Typically I only get that when it's cold, or if it had to crank longer than normal to fire.

3) It depends on the speed/gear and if the torque converter was locked up. Again, this is for emissions since the truck is almost free-wheeling at this time.

One thing to check is where the intake tube attaches to the the throttle body. If it's loose there, 1 and 2 would become more pronounced.

TPS could cause 2 or 3, but it would have tossed a code if it was faulty.

Daryl LBZ · February 17, 2013

Makes me wonder sometimes if the low idle is part of the problem with some peoples trucks having no steering or hard to turn the wheel at low idle say when backing up a trailer.

Sent from my Samsung Galaxy S3