2008 Silverado LTZ: Inconsistent shaking while idling now with a CEL

JustinB · January 14, 2012

Here are the specs on my truck:

2008 Silverado LTZ

77,792 miles

5.3 Iron Flex Fuel

4L60E trans

Ok, over the last month or so, I've noticed that while the truck is idling, e.g. red light, that there is a slight shaking feeling that I can feel in my feet and legs. It almost feels like a car does when it's having a misfire and you give it more fuel to keep it running. However, the feeling isn't as pronounced as having a bad misfire would be. It could almost feel like a motor mount going bad too.

It's consistent in the fact that the truck does it at normal operating temp (NOT), but it feels like the slight shaking is inconsistent. Sometimes the slight shaking will feel closer together between doing it, and sometimes further apart. I have noticed that it doesn't do it while the truck is warming up in the higher idle stage (open loop), but the problem appears later at NOT (closed loop).

It has really felt like a light misfire, so I changed the air filter (OEM) and spark plugs (OEM). I was going to replace the wires as well, but haven't had a chance to stop by the dealership. The airbox is sealed tightly as should be, and I made sure that all the spark plugs were gapped to .040. The wires for now appear to be in good condition with no cracking, boot problems, etc.

Tonight, while in the Walmart parking lot, the truck misfired a couple times relatively bad, the CEL flashed, and now the CEL is staying on. It was after 8:00, so I didn't get to go to Advance to get them to read the codes, but should I?

I thought that if I had Advance clear the codes, then the dealer may not want to service the truck w/o the presence of the CEL. I'm pretty confident that the CEL is the misfiring that was happening, and if the problem is a coil pack or something, will it be able to be replaced under the factory 100k mile warranty?

Also, I'll note that I only run Top Tier fuel in the truck (Exxon, Chevron, and occasionally Shell). All the fuels are E10 because the only E0 fuels around here are little mom and pop stations that are $.30 higher on the gallon (no joke). I'll also use a couple bottles of the Chevron Complete Fuel System Cleaner every so often.

Any ideas as to what the problem could be, or hopefully, whether this should be covered under warranty?

As always, any help is very much appreciated.

gmtech4 · January 14, 2012

scan it, dont clear it ,take it in

JustinB · January 15, 2012

I went to Advance this morning and the guy that read the code said it was a TPS problem. My truck is an '08 with 78k miles? Will this be covered under the powertrain (5yr/100k) warranty? I ask so I'll know in the event if the dealer tries to say it isn't. Thanks for the input.

markw8 · January 15, 2012

Not likely.

Mark

gmtech4 · January 15, 2012

i thought if its attached to the engine ,its covered

doesnt matter ,take it in and find out ,it has to be fixed ,DO NOT ASSUME its the TPS from a guy at a parts store who makes near minimum wage wanting a sale

what code was it ?

JustinB · January 15, 2012

i thought if its attached to the engine ,its covered

doesnt matter ,take it in and find out ,it has to be fixed ,DO NOT ASSUME its the TPS from a guy at a parts store who makes near minimum wage wanting a sale

what code was it ?

P0121 was the code.

If it wasn't covered under warranty, then I would replace it myself, but after searching pretty extensively, I'll probably have to take it in regards of whether it's covered or not. I've came across several articles/posts where Chevrolet techs said there was a TSB on this about cleaning the throttle body and doing the proper relearning w/ a Tech II. I don't have a Tech II, so I guess I'm just going to have to bite the bullet.

This is kind of disappointing because I bought the truck with high hopes that it'd last a long time with problems. My dad has always been a huge Chevy guy, and has always had really, really good life from his cars/trucks. The last Silverado he sold had 260k, and still ran as strong as new. I had purchased an Audi A4 back in October, but out of the couple months I owned it, I might have been lucky to have driven it 10 days. It stayed at the dealership in Greensboro/Charlotte which is about 3.5/4 hours away from home. That's why I purchased this. I don't want to have a project car/truck for a daily, and it's still under warranty for another 1.5yr/20k miles.

Hopefully, after I get this figured out, there won't be anymore problems for a while, or at all. I just hope it's covered under the warranty so I don't have to shell out another $600 at the dealership.

As always, thanks for the input. It's much appreciated.

NoMoreGM4Me · January 15, 2012

i thought if its attached to the engine ,its covered

doesnt matter ,take it in and find out ,it has to be fixed ,DO NOT ASSUME its the TPS from a guy at a parts store who makes near minimum wage wanting a sale

what code was it ?

Nope, PT warranty does not cover sensors.

gmtech4 · January 15, 2012

wasnt sure

jaredlucky16 · January 16, 2012

The dealer might be able to goodwill a throttle body for you

holty · January 19, 2012

any updates on this?

JustinB · January 23, 2012

The dealer might be able to goodwill a throttle body for you

I'm hoping so. I finally got to talk to one of my friends who's at Tech at a local dealership (~20 mi. away), and he said with the P0121 code, that they'd clean it first and if that didn't fix it, then they'd replace the throttle body. He thought that it might be covered under the Federal Emissions warranty and told me the service manager that I'd need to talk to that would try to help me out.

any updates on this?

Should be coming here in the next week or so. I haven't had a chance to get to the dealership with work and things, but am calling tomorrow to schedule an appointment for it. I did however clean the MAF, but it didn't seem to help. I was going to pull the throttle body myself and clean it, but after what my friend suggested, I'm taking to his dealership to let him work on it (see above other comment for details). From what researching I've been doing, it seems most people has cleaned or replaced the throttle body to fix. However, I've also came across a few people that said replacing the brake booster grommet seemed to fix the problem immediately. I'm going to get them to replace mine at the same time, so my fingers are crossed hoping it works out.