Bumpy/shuddering idle in drive-SOLVED

[Ultraviolet]

I’m new to the forum. I’ve owned my 2011 suburban LTZ for about a year and just paid it off! It has 130k miles. I had an issue where the stabilitrack cut out and it was running rough. I took it to my mechanic and they replaced one coil pack on cylinder 1 after the first visit since it was throwing a misfire code. Then it happened again and they changed the plugs and wires. The main issue was gone but there was still a slight stumble in drive at idle. This is something it’s done since I bought it. I added the airraid kit and got a tune from black bear (on referral from this forum - thanks!) and things seemed better for a bit. Now it’s back to stumbling at idle but no codes are being thrown. Basically when I’m at a stoplight it’ll be fine for a few seconds and when the idle drops a bit it’ll stumble as if there’s a misfire. I’m going to check that all the plugs are installed correctly ie screwed in all the way and I’ll check that the wires are fully seated. It seems to be lacking power when accelerating. I also head an intermittent ticking sound. It sounded like when a gas stove fails to light - tick tick tick tick. It didn’t sound mechanical. I’m thinking that if all the plugs check out I’ll replace the coil packs since only one was replaced by the mechanic. If that doesn’t fix it I’ll replace the plugs and wires with ac delco (I’m not sure what the mechanic put in). I’ve looked through the forum for similar problems and the fix seems to be plugs, wires and coil packs. If anybody else has any other ideas I’d love to hear them! Thanks for the great forum and helpful responses!!

 

[petethepug]

Welcome. Thorough first post. Let me crack a few questions at ya.

* Has there been any work, tune up or diagnostic on it lately?
* Fuel Pump original or replaced with an OEM unit?
* Can you fill up at gas station without the nozzle clicking off?

 

[j91z28d1]

if the ticking is a spark tick like it's jumping to ground somewhere and not making it to the plug, if you can make it do it when it's super dark outside and the hood up. you might be able to see it.

used to use that trick for the coils on the old opti spark lt1"s. pop the hood and it would be a light show. you could see where the coil of wires in the coil would break thru the dielectric and jump stright to ground.

just something to try.

 

[Fless]

Has the throttle body been cleaned lately? Idle air control working properly? (I'm not sure if you can clean the IAC)

 

[Ultraviolet]

Welcome. Thorough first post. Let me crack a few questions at ya.

* Has there been any work, tune up or diagnostic on it lately?
* Fuel Pump original or replaced with an OEM unit?
* Can you fill up at gas station without the nozzle clicking off?

The only work is a new coil on cylinder 1, plugs and wires and a tune from black bear.

Original fuel pump.

I should add that the air compressor for the rear shocks is pretty loud. At one point I thought it was the fuel pump but it’s not. Also the “service suspension system” warning comes on now sometimes. Maybe related?? Maybe not.

I can fill up without the nozzle clicking off. I use E-85. Black bear assured me that their 91+ tune is compatible with E-85.

 

[Ultraviolet]

if the ticking is a spark tick like it's jumping to ground somewhere and not making it to the plug, if you can make it do it when it's super dark outside and the hood up. you might be able to see it.

used to use that trick for the coils on the old opti spark lt1"s. pop the hood and it would be a light show. you could see where the coil of wires in the coil would break thru the dielectric and jump stright to ground.

just something to try.

My cousin told me to give this a try. Look at it at night and see if you can see it arcing. Thanks for the reminder!

 

[Ultraviolet]

Has the throttle body been cleaned lately? Idle air control working properly? (I'm not sure if you can clean the IAC)

The mechanic cleaned the throttle body. IAC I’m not sure of. The mechanic also cleaned the MAF sensor with the special maf spray.

 

[petethepug]

Cool, the e85 will of kept the tb clean as well as the combustion chambers so I’m not thinking no knock or detonation.

When the fuel pumps get around 100k, they’re suspect, but known to live to 200k+. Crystal ball says shop for a new OEM f/p & fuel carbon canister (Rock Auto & Parts Geek) that like to dump carbon pellets in the fuel system after 100k.

Ideally you need a 2 way scanner to capture the hesitation live when your driving’s.

Done the -/+ battery cables that like to invisibility rot from inside out?

Any fuel smell after start up?

Be aware if you do take it in for a general tune up, the base tune is calculated off Petrol, not e85. That means bring it in for service after running a tank or 2 of petrol as a tb recalibration service won’t work off e85 running across the o2 sensors. Ask me how I know. My techs knew I ran e85 and had to drain it. Fortunately it was during the f/p replacement.

Just saw last post. An ahHa moment. Run the e85 out. Fill with petrol for a few 100 miles and take it back for a tb calibration and MAF clean. If that was done on e85 it’s confused

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Are you using a quality bi-directional scanner (like a Tech 2 or equivalent)? Many cheaper scanners cannot access many deeper trouble codes.

 

[Ultraviolet]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Are you using a quality bi-directional scanner (like a Tech 2 or equivalent)? Many cheaper scanners cannot access many deeper trouble codes.

I’ll upload some photos when I’m back home. I’m out of town at the moment.

My scanner is the EFIlive AutoCal from Black Bear. When I get home I’m going to hook it up and see if there are any codes. No engine lights at the moment. Just the “service suspension system” that comes on occasionally. I suspect that it’s not related to the shudder.