Advice needed on throttle sticking/rev hang

[Aldo0280]

I have 2016 gt manual with gt350 im, tb, & pmas cai, happens mostly in 3rd or 4th gear around 3500-4500 rpm when i let off the gas car keeps going same speed for 15-20 seconds sometimes more like i have the cruise control on? Tuner says he thinks my tb might be bad. I dont have any codes & when i first purchased the car a few months ago it came with a tune but no tune device so i had to flash back to stock & start over & it didnt do it with the original tune. So im not sure if my tb has developed an issue or if its the tune or tunes? It does it with every revision ive gotten. Other than the rev hang the car runs great. Debating weather i should just order another gt350 tb off ebay to rule it out? I recently changed the plugs, done a couple smoke tests, cleaned maf, removed & reinstalled intake manifold (diff issue) & always same rev hang? It seems to get worse the longer i drive it after switching tunes. Very much appreciate any advice!

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[Deleted member 69311]

Correct me if I’m wrong, but could it be your clutch is too hot? I have bad rev hang when my clutch is hot. When it’s 85°+ outside, and I do a hard pull and shift hard, I get terrible rev hang. It sucks when I’m doing a pull and going about 100mph, 5k+ rpm, and I go to shift, the gear goes in, the clutch comes out, and the revs hang for a second, then it jerks the car pretty hard.

 

[Aldo0280]

Im not sure about that? Mine basically acts like i have the cruise control set when i let off the gas to coast & it stays like that for 15-20 seconds. Even if i push the clutch in it still holds the revs but not as long. I usually leave the clutch out & push the brake enough to slow down before it will coast or decelerate? Ive never really noticed it happening in 1st or 2nd but 3rd to 5th it does it almost everytime i try to coast doesnt seem to do it much in 6th either?

 

[ice445]

My car used to do this but I never figured out why lol. Went away after a while. My best theory is that throttle closure after a pull creates a ton of vacuum and pulls some oil vapor through that the car just runs on for a little bit. Could be pcv valve related. I did swap mine at one point but I don't know for sure if that fixed it. Switching to a quality 5w30 may help as well since it has more temperature stability.

 

[Aldo0280]

I have a upr catch can setup so i wouldn't think im getting very much oil vapor in the intake track? I actually found a brand new gt350 tb on ebay & the guy just accepted my offer of $115 bucks so i guess ill know for sure here soon if its an issue with my tb or my tune. I also have a gt350 cai that even though ive read isnt as good as the pmas i have i do like how it looks & would rather run that cai but my car runs even worse with the gt350 cai. Tuner sent me multiple revisions trying to get it right but ended up telling me to put my pmas back on & sell the gt350 cai haha. Not only would the throttle basically stick even worse but it would also hold the revs up around 1200-1500 for 30 seconds or more. That im sure had to be tune related & is what also makes me think the current issue with my pmas cai installed is also tune related?

 

[K4fxd]

Are you gorilla tightening the TB clamp? The GT350 cai tune is cake, if your tuner can't get that right he doesn't know what he is doing or there is something wrong with the CAI.

You are GEN 2, the 350 TB is not easy to tune. You would be better off using your 80mm TB with an adapter so it fits the 350 manifold. Then the stock TB tune can be used. VMP makes a very good adapter, so do others.

If it is hanging as long as you say it should be easy to see in the logs.

 

[Aldo0280]

Well idk if i gorilla tightened it but it is definitely tight. I attached a video but i should have rolled down my windows or smthen because its kinda hard to hear but at the very beginning u can me accelerate a lil & then i let off & im not touching anything for the rest of the whole video. Then at the very end if u listen close u can hear the exhaust note change when it finally started to decel? Whats also weird is it doesn't always do it sometimes it only does it for a couple seconds. I think it mostly depends on what gear im in & what rpm im at when i let off? Any ideas?

 

[Aldo0280]

Well i thought i attached a video? Ill try again? Ok i figured out i have to upload it to u tube then here? Hopefully this works?

 

[Aldo0280]

Idk after watching the video a few times the rpm's are slowly dropping but it doesnt actually feel like its decelerating until rite at 21 seconds into the video when u hear the exhaust note change a lil? In the video i let off the gas at 2 seconds in & dont touch anything after that. Also when i let off in 1st or 2nd it decelerates right away like normal?

 

[K4fxd]

Can you attach a log? logging TB actual TB requested, pedal position, RPM.
Any and all pid's having to do with TB and Pedal nothing else except RPM

 

[Aldo0280]

Hey thank u very much for the help k4fxd! How exactly should i drive in the log? Like normal or try to get the throttle to hang like in the video? Im setting up the pid's now & will go make a log shortly

 

[K4fxd]

Make it hang.

 

[K4fxd]

What you are looking for is to see if the TB is following what the pedal is commanding.

Turn everything on high res. You should have very few channels.

 

[ice445]

What you are looking for is to see if the TB is following what the pedal is commanding.

Turn everything on high res. You should have very few channels.

That won't really tell you much, since the ECU ultimately controls the throttle. The torque demand request (the pedal) is just one factor that it looks at. In this case the ECU is probably intentionally holding it for some emissions related reason(AFR, cat overtemp, etc). The only useful data you can gather is if the pedal output itself is returning to the same value as it is at idle when it's not being pressed, since I suppose a bad throttle pedal could cause something like this.

I wish I could have figured out why my car was doing it, but then it stopped. I do know that I could just double clutch and it would start falling again as normal though. It's also wroth noting some rev hang is unavoidable on these cars, at least on the stock tune. The fact you have an aftermarket tune makes me wonder if that has something to do with it. Did you ever check your adaptive fuel trims?

 

[Aldo0280]

im pretty new to the datalogging & idk how to turn on high res & i also dont know what the channels are? but i did a couple logs although now i cant figure out how to upload them here?

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