12' Tahoe 5.3 rough idle ? Heeeelp

Hugeroost · December 1, 2019

Hey guys, my daughter called said her tahoe was running really rough, so I had her bring it over. I thought a California tuneup would cure it because it was just a rough idle, so cleaned the TB real good, very dirty intake, put 10gal of premium and a bottle of Techron and took it out and ran it. Truck was pullin strong till it hit 95 and shut down lol. By the time I got back home it seemed to be much better, ah the ole Cali tune, thats 400 bucks there. She called a week or so later and it was back again, she ended up taking it to a local shop, she called me crying, the dude told her she would need a motor for 7k, said he see's it every day. I went and got the truck just so I could dog him, but he stuck to his guns. Lifters or whatever, but said compression test showed good on all 8. I drove it back home, when you pull up to a SS or red light you can feel the rough idle, as soon as you take off it goes away amd runs great. SO ??? I'm thinking one of those Range Tech AFM bypass plug in things for 200 bucks, this engine runs too good for anything serious to be wrong. I reckon you fellas got this shyt all figured out, ole Roost still sportin a 454 with a damm carburetor on it so I dont know about all this hi tech stuff. That big block you just touch the key and it fires off, and proceeds to get that good 9-10-11 mpg all day long. Thanks guys

CamGTP · December 2, 2019

The AFM/DoD isn't active at idle or low speeds so not sure how much that disabler is going to do for you.

If you want to test this you can put the truck in the manual mode with the shifter. Put it in M4 or M5 and go for a drive. That is going to disable the AFM/DoD system, so if it still idle's rough when you come to a stop, that Range product isn't going to help you any.

It could need new spark plugs and wires too. I'm only guessing without seeing some live data on my scanner to watch what is going on.

swathdiver · December 2, 2019

19 hours ago, Hugeroost said:

Hey guys, my daughter called said her tahoe was running really rough, so I had her bring it over. I thought a California tuneup would cure it because it was just a rough idle, so cleaned the TB real good, very dirty intake, put 10gal of premium and a bottle of Techron and took it out and ran it. Truck was pullin strong till it hit 95 and shut down lol. By the time I got back home it seemed to be much better, ah the ole Cali tune, thats 400 bucks there. She called a week or so later and it was back again, she ended up taking it to a local shop, she called me crying, the dude told her she would need a motor for 7k, said he see's it every day. I went and got the truck just so I could dog him, but he stuck to his guns. Lifters or whatever, but said compression test showed good on all 8. I drove it back home, when you pull up to a SS or red light you can feel the rough idle, as soon as you take off it goes away amd runs great. SO ??? I'm thinking one of those Range Tech AFM bypass plug in things for 200 bucks, this engine runs too good for anything serious to be wrong. I reckon you fellas got this shyt all figured out, ole Roost still sportin a 454 with a damm carburetor on it so I dont know about all this hi tech stuff. That big block you just touch the key and it fires off, and proceeds to get that good 9-10-11 mpg all day long. Thanks guys

It's near impossible to properly diagnose or work on these trucks without a proper scan tool. You could get one of those OBDII adapters that talks to your phone, download the Torque Pro app for $5 or DashCommand for Apple phones. Anyhow, you want to see exactly what codes are being thrown and then monitor the engine sensors to determine the source of the misfire.

I'm no expert but such a rough idle and then drives normal does not seem to be AFM related nor cause for a complete engine.

bg1988 · December 4, 2019

a vacuum leak un-metered air is entering the engine... as well as a faulty MAF

after that you will need to drive it 30 miles or so , so the computer can learn to idle...

Edited December 4, 2019 by bg1988

Hugeroost · December 4, 2019

bg, the tuner guy didnt see any vacuum leaks, I'll clean that MAF today before I take off and see if that helps.

On 12/1/2019 at 7:38 PM, CamGTP said:

The AFM/DoD isn't active at idle or low speeds so not sure how much that disabler is going to do for you.

If you want to test this you can put the truck in the manual mode with the shifter. Put it in M4 or M5 and go for a drive. That is going to disable the AFM/DoD system, so if it still idle's rough when you come to a stop, that Range product isn't going to help you any.

It could need new spark plugs and wires too. I'm only guessing without seeing some live data on my scanner to watch what is going on.

Hey Cam, so I hired a tuner to come over and do just that. He turned AFM off, said #8 had a misfire, also said the AFM would not be engaged at idle. He wanted me to put a bottle of seafoam in the crank case and run it 100 miles or so, drain it, and put Mobil 1 10w-40. He thinks it may go away, it does seem to be getting better, I only have put about 30 miles but today I'm driving up to the ranch and that's over 100 miles round trip. When I get back tomorrow I'll change oil, he said put a bottle of Lucas in that oil. He said he's seen that AFM really tear up lots of motors, hopefully I caught it in time. I think everybody that owns a 07-13 should somehow be warned, and that AFM should definitely be turned off, its fukin useless to begin with, I mean its 1-1.5 mpg difference who gives AF about that if your motor is in danger. What's Cam think

Mikebtte · December 4, 2019

3 hours ago, Hugeroost said:

bg, the tuner guy didnt see any vacuum leaks, I'll clean that MAF today before I take off and see if that helps.

Hey Cam, so I hired a tuner to come over and do just that. He turned AFM off, said #8 had a misfire, also said the AFM would not be engaged at idle. He wanted me to put a bottle of seafoam in the crank case and run it 100 miles or so, drain it, and put Mobil 1 10w-40. He thinks it may go away, it does seem to be getting better, I only have put about 30 miles but today I'm driving up to the ranch and that's over 100 miles round trip. When I get back tomorrow I'll change oil, he said put a bottle of Lucas in that oil. He said he's seen that AFM really tear up lots of motors, hopefully I caught it in time. I think everybody that owns a 07-13 should somehow be warned, and that AFM should definitely be turned off, its fukin useless to begin with, I mean its 1-1.5 mpg difference who gives AF about that if your motor is in danger. What's Cam think

You got lucky, I have seen a few people be able to catch it and other get the new engine option. Keep in mind that the engine was starting to see failures and the AFM disable may or may not be a long term fix. I had a similar lifter issue at 100K and did AFM delete and never had another issue for 60K miles.

As for warning everyone, that has been an ongoing issue without a cure. Guess there will come a time when all remaining 07-13 GM's will have the AFM delete.

Hugeroost · December 5, 2019

On 12/4/2019 at 12:47 PM, Mikebtte said:

You got lucky, I have seen a few people be able to catch it and other get the new engine option. Keep in mind that the engine was starting to see failures and the AFM disable may or may not be a long term fix. I had a similar lifter issue at 100K and did AFM delete and never had another issue for 60K miles.

As for warning everyone, that has been an ongoing issue without a cure. Guess there will come a time when all remaining 07-13 GM's will have the AFM delete.

Well hopefully so, I aint outta the woods yet. I am getting Traction = Off. And then Stabilitrac = Off. I dont know if that means I should turn both on or what. It seems to be running much better though but still have a little racket in there. Hopefully when I dump this oil and put rhe new w a bottle of lucas it'll get better, the rough idle is almost gone

Hugeroost · December 5, 2019

Well today is the day I dump the oil with seafoam in it, it was pretty new oil so we'll see how dirty it is. Going back with Mobil 1 10-40 high mileage, its all I could find in 10-40, gonna put a quart of synthetic Lucas with it. Side note, glad the tuner brought up being sure to get the fully synthetic Lucas, I would not have paid attention to that.

Hugeroost · December 17, 2019

ok guys so i am still getting alot of clatter, rough idle is back. One thing i did not do because of my big hands etc was change out that oil sending unit on the back of engine, could it be possible that filter is partially clogged causing lifters to not get enough oil and clatter. I know thats a cheap thing to do just a PITA to get to it, could it be that simple, meaning changing this could fix my problem, man that would be nice.

So if that dont work i guess next step is to buy the kit and totally delete the AFM, cam, lifters, etc. Can anyone link me to a thread where someone has done just that, and is that a worth while fix. The wife wants to get rid of it, trade it in, but i figure the dealer will kill me on trade in because they know it will need to be done, so i figure i'll get ass-raped there right off the bat.

Mikebtte · December 18, 2019

That oil sender only reads to the dash. Should not effect the engine operations.

Here is an AFM delete. Cam/lifters and all. If you want to keep the truck for many more miles the delete kit is worth while. If you don't want to keep it than the wife might be right, let the dealers have it.

Texas speed and many others offer a kit or you can build a kit at summitracing.com as I did.

Edited December 18, 2019 by Mikebtte