[SOLVED] Intermittent Stumbling at low loads only

Hey guys real desperate to figure out what’s been going on with my car. Having this issue where it will “stumble” only at idle or while taking off from a stop / cruising. It’s fine at medium-wot. It started about 3 weeks ago. Was perfectly fine before then with the exact same setup nothing changed.

Let’s say for example I slowly take off from a stop in 1st it feels like it hits a brick wall then continues on. Like the fuel cut when you overboost. This only happens at under 3K rpm’s. And it doesn’t happen every time it’s so intermittent I can barely catch it on a log.

So far I’ve tried cleaning the spill valve, cleaning the MAF, swapped out the PRV that helped a bit but still happens.

Maintenance done (past 10K)
-Valves cleaned
-Injectors cleaned / flow tested with new GB seals
-PCV valve (OEM)
-Purge valve (OEM)
-Primary o2 sensor (NTK)
-MAF sensor (DENSO)
-PRV (OEM)
-Smoke tested no leaks

Mods
-Cobb Accessport Stage 1+SF
-Cobb SF intake
-CPE HPFP
-Denso ITV20 gapped to 0.28
(Please keep your opinion on OTS tunes to yourself, the car was running perfectly fine on the same setup for over a year before this issue started a few weeks ago. So don’t blame the tune.)

Will post a log of the issue happening while idling if anyone can take a look I’d really appreciate it. Thanks.

 

Probably the wrong place to post that comment about OTS tunes. I can tell you pretty much everyone here will bring that up. Best of luck!

 

Im not here to argue Im willing to go and buy a protune right now but that won’t fix this issue? il just be told to fix the issue before tuning continues sooo…. Would be nice to get actual advice

 

99% tune issue

1% Check battery voltage when disconnected check wiring to MAF

 

Thank you for the voltage advice will check

 

oh the datalog isnt even posted it wouldnt let the link go through il try uploading it

 

i think ive uploaded it now?

 

Not arguing at all just pointing out how this community is.

How many miles are on your car? How old are the spark plugs?

Also take a look at the format for the troubleshooting template at the top of this sub forum and add any info you haven't as it may help.

 

155,000 miles

Now that you bring up spark plugs the issue actually started 3 weeks ago right after I put in NGK 6510 gapped at 0.28 I ran them for a few days but was having this issue so I read online and realized your not supposed to go one step colder unless your running 100hp more then stock so I went back to Denso ITV20 which is stock heat range but the issue remained unfortunately.

 

The ots tunes do some weird hybrid boost/load tune that is based on 2009 knowledge of these cars. The tunes are really old and have not been updated to even use all of the tables that are available now. A new tune would approach things in a completely different way.

That said I dont think that the tune is likely your issue but it shouldn't be ruled out. Especially with the hybrid tune and it just getting to the part of the calendar where temperatures drop it could be screwing up.

 

I Was thinking about it and while the temp could play a part in it, I was running the same setup all through last winter and didn’t have these problems, really hoping it’s not some electrical issue that will take forever to track down

 

SOLVED: Belt and tensioner pulley were failing I guess, noticed tears in the belt so replaced with brand new parts and so far so good.