Bumpy/shuddering idle in drive-SOLVED

[Ultraviolet]

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

No fuel smell after start up. I have not replaced the battery cables. I did replace the battery when I bought it. To be clear I don’t exclusively use E85. I use it when I’m in the area of the e85 station. Right now it’s filled with e85 but a week ago I had regular gas in it.

 

[petethepug]

Interesting, no codes & stumble. Another bad coil would likely throw a DTC. Search for new codes and if possible capture while stumbling, keep the Reg gas in for a while.

Replace the charcoal canister & inspect for pellets getting through. After that, the tech2 or equivalent will find out what it is if the MAF & tb are calibrated off Reg gas.

 

[Fless]

I wouldn't recommend throwing an evap canister at it as long as you aren't getting any evap codes, especially since you don't have trouble filling the tank. That's just a distraction. Concentrate on other areas since an evap problem usually doesn't cause driveability issues. Having said that, an intermittent or open evap purge valve (on the engine) COULD cause issues with idle, but that's not the canister's fault, and you'd have evap codes if it was bad. Easy enough to verify with a purge-and-seal test.

 

[Ultraviolet]

I’m going to start with checking the most recent fixes for mistakes. The shop is good but they can be sloppy. I was changing the headlights and found an old spark plug that they must’ve dropped. I’ll be home in a few days and will report my findings. Thanks for all the helpful direction!!

 

[Ultraviolet]

One more quick question, does anybody know if the autocal will read the service suspension warning code? I want to get to the bottom of that issue too. Hopefully it’s the compressor.

 

[Geotrash]

One more quick question, does anybody know if the autocal will read the service suspension warning code? I want to get to the bottom of that issue too. Hopefully it’s the compressor.

It won't. You'll need a scanner that can read all of the modules. I use one of these and it works fine for all of the modules on these. There is an additional cost for the GM module through the app once you buy the dongle, but it's still comparatively cheap. https://a.co/d/2kH2U1Z

 

[Joseph Garcia]

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.

I have an AutoCal, and it doesn't read trouble codes to the deep level that you need to properly diagnose your issue.

I suggest that you take the recommendation from @Geotrash, as for that price, you can't go wrong.

 

[j91z28d1]

It won't. You'll need a scanner that can read all of the modules. I use one of these and it works fine for all of the modules on these. There is an additional cost for the GM module through the app once you buy the dongle, but it's still comparatively cheap. https://a.co/d/2kH2U1Z

I was wondering about that one.. how much is the add on gm stuff and is it one time, or reoccurring?

the topdon I have is useful enough, no paid addons for a year, but after a year it's another 50$. I like they thing enough I might end up doing it, but they also have a higher level 100$ one I might try instead, or I was looking at the one you linked to as a try out too.

 

[Ultraviolet]

I hooked up the autocal and proceeded to monitor the data. I used the E38 misfire PID and it looks like cylinder 3 has a misfire. The count increased with each shudder so I’m pretty certain that’s a strong clue! It’s not throwing a code though.

Questions: What is the firing order for the 5.3? Does anybody have a key for what all the readings are on the autocal? I can figure out some of them but many I can’t decipher what they are.

Plan is to swap cylinder 1 coil with cylinder 3 and see if the issue follows the coil. Fingers crossed!!

Here’s a video

 

[Ultraviolet]

Update. I swapped the coils and there was no change so I put them back and swapped two plugs. In the process I saw one was cracked. The misfire followed the cracked plug so I changed them all to new. All better now!! Thanks for all the help, this forum is great!!