2004 Tahoe 5.3 weird idle

[Alan's Classic]

I'll do my best to explain this.

Runs great at all RPM's except at idle. At idle it has an erratic skip. Sometimes it is barely noticeable and at other times it drops low enough to make the lights dim. I notice it more when it is warm. When cold it runs smooth.

There are no check engine lights on. It has about 145K on the clock. It also happens with AC on or off. If I two foot it and bring the idle up about 100-200 rpm it is still noticeable.

Any suggestions will be greatly appreciated.

[clinebarger]

Clean the throttle body bore with some carb cleaner.

[77chris03]

my 03 z71 5.3 did the same thing.... its "somewhat" normal i guess. does it to my dads too... but his is a 6.0. put it on a snap on live diagnostics and it is a mix with ethonal gas. only happened if i ran 87. I cleaned throttle body, votec plenum, etc. and it still did it. i ran 89 or 93 mix with 87 and lucas upper cylinder lubricant and it went away. but comes back when i ran with plain old gas.....now that i have a new truck 2010 with the 6.2 i notice it does the same just not as bad. i run a mix of 93 and 87 and no problem so far..with the lucas too of course...

[77chris03]

may want to replace plugs and wires...that helps too....

[Alan's Classic]

Thanks guys I'm sure it needs the throttle body cleaned. I just put some Lucas injector cleaner in yesterday. I don't know what's been done as far as maintenance. I just bought it about two months ago. I should go ahead and change the plugs etc. I'll post the outcome.
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[bighaas79]

check fuel pressure regulator as well.

[Alan's Classic]

Hadn't got to do much yet. I did buy some E3 plugs. Then I pulled one out for a comparision. i don't think they need changed, what do y'all think? I only pulled one. The idle is getting noticeably worse. The throttle body is next, I hope to get it cleaned tomorrow.

[clinebarger]

I run Delco or NGK plugs. I dont recommend running any type of "gimmick" spark plug.

If it idles worse when its cold......Intake gaskets are known to cause this symtom. If it they have never been replaced.....I would replace them as a maintainence item at 148K.

[bighaas79]

I have to agree. Put delcos back in it. If you do some looking you will see there have been instances where the gimmick plugs are the issue.

[usmcchevy]

X3 Get a good set of normal plugs. Platinum or Iridium are fine, just no multiple electrode/power enhancing gimmick junk like Clinebarger and bighaas said.

[Mechanic77]

Originally Posted by clinebarger

I run Delco or NGK plugs. I dont recommend running any type of "gimmick" spark plug.

If it idles worse when its cold......Intake gaskets are known to cause this symtom. If it they have never been replaced.....I would replace them as a maintainence item at 148K.

+1 on the intake gaskets.....I've run in to two of them in the last few months. The best way to know for sure is to use a smoke machine and smoke the intake....you'll see smoke coming out at the gasket if you have a problem

If you do the intake gaskets, I would recommend getting the better Fel-pro gaskets that are molded rubber over steel frame instead of the stock plastic holder with a seal.....do it once and be done with it

[Alan's Classic]

Thanks for all the input. I finally cleaned the TB today. Very cruddy inside. I thought for sure that would fix it. I would say it helped. The idle doesnt fall off as much as before. It does still have a noticeable drop in RPM at idle. It feels like a little shake in the seat. Until I can go get some AC plugs, should I unhook the battery to reset the computer? Does the ECM have a memory of the way it was running. I'll post pics tonight of the TB.
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[truckdude239]

those e-3s will cause the coil to burn up if not carefull best plug for that truck is the ac delco 41-110 Iridium plugs runn 9-11 dollars each but they will run 100k miles with no changing, the e-3's are a resister plug which will not let all the energy from the coil though

[Mechanic77]

Originally Posted by Alan's Classic

Thanks for all the input. I finally cleaned the TB today. Very cruddy inside. I thought for sure that would fix it. I would say it helped. The idle doesnt fall off as much as before. It does still have a noticeable drop in RPM at idle. It feels like a little shake in the seat. Until I can go get some AC plugs, should I unhook the battery to reset the computer? Does the ECM have a memory of the way it was running. I'll post pics tonight of the TB.
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You can try disconnecting the battery to clear the memory, but it hasn't worked for me on the last couple I've cleaned the throttle bodies on.....I don't have a Tech II (factory gm scan tool) to do the idle relearn with....but just driving it will cause the ecm to relearn it on its own.

Does it idle any better after it's fully warmed up? That would be another indication of an intake gasket issue.....they usually idle worst when they're cold, and get better as they warm up when everything expands from the heat....

[Alan's Classic]

Originally Posted by truckdude239

those e-3s will cause the coil to burn up if not carefull best plug for that truck is the ac delco 41-110 Iridium plugs runn 9-11 dollars each but they will run 100k miles with no changing, the e-3's are a resister plug which will not let all the energy from the coil though

I will definitely go with the AC plug. Thanks

Originally Posted by Mechanic77

You can try disconnecting the battery to clear the memory, but it hasn't worked for me on the last couple I've cleaned the throttle bodies on.....I don't have a Tech II (factory gm scan tool) to do the idle relearn with....but just driving it will cause the ecm to relearn it on its own.

Does it idle any better after it's fully warmed up? That would be another indication of an intake gasket issue.....they usually idle worst when they're cold, and get better as they warm up when everything expands from the heat....

It idles fine when cold. Once it comes up to temp is when it starts erratically dropping RPM with AC compressor on or off.
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[Alan's Classic]

I can't post pics tonight, because I can't find my DL cable for the camera. Home improvements suck. Anyways.........

I read some where to clean the MAF. I started thinking about it and one thing I didn't mention is there is a K&N air filter installed. Maybe the oil from the filter has put a film of oil on the MAF and dust has accumilated on the sensor. Thoughts??

I picked up the AC plugs today as well and didn't have time to install them. After driving home the idle doesn't seem much better.

I'm just trying to do the simple things first. I'd like to do a smoke test, but don't have access to a tester. I can check around and see if someone I know has one.

Is there a specific ohm range on the plug wires? Or should they just be changed? I really don't want to replace parts if not needed. I really don't know if they are original or not. If they are original I would say it is time to replace them like someone mentioned before.

[Alan's Classic]

Update: the AC plugs seemed to have fixed the problem as of right now. I let it idle up to temp without any drop off. I'm confident that it is fixed. Before I would have noticed it once it warmed up. Thanks for all the help guys. Y'all rock.
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[truckdude239]

another sotry off crapy e-3"s glad the plugs fixed it

[Alan's Classic]

Originally Posted by truckdude239

another sotry off crapy e-3"s glad the plugs fixed it

Pics as promised. I did put antiseize on the plugs. I almost forgot.

[Boog]

So Alan is it still idling ok for ya?

[Alan's Classic]

Yes Sir, no complaints.
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