Diablosport Forums

I was running 87 octane tune on a 2012 Colorado Sport 5.3 for a few months with no issues but it seems as the weather turned colder the truck has developed an odd intermittent stumble right before it lights off at startup. I have returned the truck back to the factory tune and it seems to have gone away but being that it is intermittent I cant say for sure whether on not it fixed the problem. It almost sounds like a timing issue. This is only at startup. Once it starts it seems to run fine. Has anyone seen this before? Could it be the winter blend of gas here in Cincinnati? I've been running Sunoco 87 octane.

Forgot to mention that I have a K&N filter and Dynomax single exit cat back.

well, there is nothing in the tune that would affect cold start, Id guess its truck related somehow.

Remove and clean your MAF sensor and the Throttlebody... it is due.

Update:
After running the truck for a week with stock tune I haven't had any issues. I pulled the MAF sensor and cleaned it last night and reinstalled the 87 tune and hard shift tune. After I installed the tunes I realized I hadn't updated the intune since I installed them in the summer (2014). I updated the intune and reinstalled the tunes. Running the truck with the stock tune ECM and TCM was a real eye opener. The 87 tune and hard shift tune really make the truck run like it should. I'm keeping my finger crossed.

Well the stumble is back. I also notice the hard shift TCM tune is less aggressive than the previous tune that I had installed before the updates. it took about an hour for the updates to finish and mentioned something about updates for GM or Chevrolet. Was there any changes made to the TCM tunes for my truck in the latest updates?

The truck is going back to stock tonight. its a real shame because I like the way the truck runs and responds with the canned tunes installed. I was planning to get a Diablew tune in the spring but its starting to get frustrating now.

If you would post your tunes up I'll take a look at them.

these are the 87 octane and hard shift tunes last intalled.

Can you please post the Backups as well?

sorry bout that. here they are

Hmm.. There aren't any changes in that tune that would remotely mess with start up. Is this something that developed after having the tune install for a while?

yes, ive had the tune installed since august of this year. the statrup issue started about a month ago.

any ideas on why my latest TCM hard shift tune is less aggresive than previous? I havnt changed any paramters.

The transmission tune hasn't changed since September of last year, so they're aren't any changes there. IF you would, please load this tune up and let me know if the stumble is still present.

Will do, thanks Zach. I assume this is an 87 octane tune?