V1 RPM Fluctuations/Stalling

[YoungGun]

When I simply turn the car on it idles steady, but as soon as I start driving or revving the engine then I come to a stop the RPM starts fluctuating between low hundreds and 2K and often stalls the engine. It's easy to turn the car back on again and continue driving.. until the next stop sign or stoplight.. Pretty much stalls or starts revving wildly at each stop.

Also, I used to think I needed more practice controlling the throttle due to it's touchiness, but I think the issue is car-related too. When I come to a stop, put it in neutral, then hold the throttle at 1.5K RPM with my foot as steady as possible the RPM will still fluctuate 500 RPM or more. Obviously if the car was in 1st or 2nd gear this same issue will result in the car lurching forward enough to oscillate my foot on the pedal, however, when in neutral at a stop it's apparent that it's not my foot causing the issue.

I haven't extensively tested this, but it seems like at higher RPMs it runs smoother, 'possibly' just a idle/low RPM issue. No issue accelerating besides the fluctuation causing jerkiness when I try to keep it steady.

I have cleaned the throttle body with throttle body cleaner, as well as cleaned the MAF sensor with MAF sensor cleaner. I've also ensured that the air intake hoses are sufficiently clamped down.

This is an LSJ, TVS, tuned, I believe 60lb injectors.

Appreciate any suggestions for what I should try to fix.

 

[Desert Sasqwatch]

MAF pointed in the right direction - arrow towards the intake. Any vacuum hoses disconnected or leaking? Is the brake booster good and not failed - which may allow air back into intake. No leaking intake manifold gasket? There are several things that can allow unmetered air into the intake and cause the ECM to hunt for idle equilibrium.

 

[YoungGun]

I need to double check the MAF sensor direction, but I believe it is. It didn't want to go in backwards anyways. Is this the vacuum hose you are talking about?

https://www.reddit.com/r/MechanicAdvice/comments/d0n782

I didn't build this goblin so I'm learning what everything is right now. Is this the brake booster line you're talking about? https://www.cobaltss.net/forums/2-0l-lsj-performance-tech-47/vacuum-line-brake-booster-lsj-327631/

I'm assuming I'd need a smoke machine to test for leaks on the intake manifold gasket?

 

[Chubbs]

Mine did the exact same thing. It was completely tune related.

I was able to halfway fix it by raising the idle by 100 RPM. Large injectors don't idle very well, so boosting the idle speed helped.

What really helped though was when I just copied a canned tune (I think it was a stage 2 from zzp) and then used that tune as a basis for my own tuning. I'm not sure what zzp did differently, but just flashing a new tune completely fixed my idle issue. It made the car slightly less touchy as well, although it didn't completely fix that issue.

I'm a bit surprised with the TVS you only have 60 lb injectors. Don't they recommend 80 for that setup?

 

[YoungGun]

Mine did the exact same thing. It was completely tune related.

I was able to halfway fix it by raising the idle by 100 RPM. Large injectors don't idle very well, so boosting the idle speed helped.

What really helped though was when I just copied a canned tune (I think it was a stage 2 from zzp) and then used that tune as a basis for my own tuning. I'm not sure what zzp did differently, but just flashing a new tune completely fixed my idle issue. It made the car slightly less touchy as well, although it didn't completely fix that issue.

I'm a bit surprised with the TVS you only have 60 lb injectors. Don't they recommend 80 for that setup?

Interesting. Well I just bought this goblin off JERMzSS, so not sure about the injectors. Is that tune job something a noob could do?

Are you near Overland Park, KS btw? Someone mentioned you might be in the area.

 

[Rttoys]

Did you get HP tuners with the car?

I would say tune too or even fuel. Is it set to run in E85 only? With that many mods (especially the tvs) a proper tune is key. It may have run fine for the original owner, but a change in elevation or even fuel could mess it up.

posible vac leak. You can spray carb cleaner on the intake mating surfaces and even in the injector area to make sure there’s no leaks. If there is a leak, you’ll hear a rpm change.

 

[Chubbs]

Tuning definitely isn't something for a noob, but I also think it's a necessary skill if you have a modified ecotec.

Before you start tuning though, was the car ever idling right? If the car was put together and idled like that from the beginning, then a tune is likely your issue. If it was running perfectly and then all the sudden started idling poorly, I'd be looking at other defects. A tune isn't going to change over time, it's not like it can wear out or break.

Anyway, there are entire threads about tuning, and it's a pretty long process to get started. You'll need a wide band O2 sensor, a copy of HPtuners software, you'll have to start logging data.... It's a whole process.

I'm actually on the opposite side of the city from overland park, I'm in the Liberty area up north.

 

[YoungGun]

Did you get HP tuners with the car?

I would say tune too or even fuel. Is it set to run in E85 only? With that many mods (especially the tvs) a proper tune is key. It may have run fine for the original owner, but a change in elevation or even fuel could mess it up.

posible vac leak. You can spray carb cleaner on the intake mating surfaces and even in the injector area to make sure there’s no leaks. If there is a leak, you’ll hear a rpm change.

Nada on HP tuners. No E85, i think he had 93 in Arkansas and I have 91 in Kansas.

What do you mean intake mating surfaces? So you start the car, leave running in neutral, spray some carb cleaner wherever you said and wait for a few hundred RPM change?

 

[YoungGun]

Tuning definitely isn't something for a noob, but I also think it's a necessary skill if you have a modified ecotec.

Before you start tuning though, was the car ever idling right? If the car was put together and idled like that from the beginning, then a tune is likely your issue. If it was running perfectly and then all the sudden started idling poorly, I'd be looking at other defects. A tune isn't going to change over time, it's not like it can wear out or break.

Anyway, there are entire threads about tuning, and it's a pretty long process to get started. You'll need a wide band O2 sensor, a copy of HPtuners software, you'll have to start logging data.... It's a whole process.

I'm actually on the opposite side of the city from overland park, I'm in the Liberty area up north.

It was idling like that from beginning. No change. I think it can be harder to detect if you are ripping it around without stopping or possibly if you gradually slow down instead of abruptly. But if you quarter mile to a stoplight its very apparent.

Any chance I could take it to a tune shop and have them atleast get it driveable in the meantime?

 

[Ross]

Not sure how close you are to Rogers Arkansas, but if you want to bring it buy my shop, we can take a look at it. I have HP Tuners, and could run some data logs. Have you checked for any OBDii codes?

 

[Rttoys]

What do you mean intake mating surfaces? So you start the car, leave running in neutral, spray some carb cleaner wherever you said and wait for a few hundred RPM change?

intake to head
charger to intake
throttle body to charger
any vacuum connection

Start, idle and spray. don’t want to spray a lot, it is flammable, but you’ll hear a change in rpm immediately if there’s a leak.old school diagnosing.

I’m still thinking tuning though, but gotta check the basics. Hell, pull the plugs and read them. They may give you a clue.

Get a scan tool and look at data. May be something there.

 

[YoungGun]

Not sure how close you are to Rogers Arkansas, but if you want to bring it buy my shop, we can take a look at it. I have HP Tuners, and could run some data logs. Have you checked for any OBDii codes?

That would be amazing. I'm a newbie at all this so I could easily see myself spending a month literally spinning my wheels and spending hundreds buying and testing random sensors/filters/tubes/parts that ultimately may not make a difference.

Says I'm 3 hours away. I suppose I could get a flat tow kit and tow it behind my Camaro lol.

 

[YoungGun]

Just tried idleing then pulling the maf sensor connection. It seemed to stabilize a bit. It was still sluggish and having slight hesitation and fluctuations. Didn't thoroughly test this by driving around though.

Also tried starting with maf sensor out, resulting in the car starting but then immediately stalling.

It's weird, because it's not consistent. Sometimes the RPMs will return to a stable 1K after revving, other times it gets thrown for a loop or has trouble.

 

[Chubbs]

Assuming the car is in good running condition (no intake leaks, no codes, etc)....I think my next step if I were you would be to contact ZZP, and see if they have a canned tune that would work with your setup.

That's probably blasphemy to some on these forums who tune their own cars. And I understand their logic; a canned tune isn't the "best" tune for anyone. It's a compromise to try to make a single tune work for a bunch of different cars so ZZP can make money. But what a canned tune does well, is that it works for most people, under most conditions, most of the time, and it probably won't blow up your motor. And for most of us, that's good enough.

Unless you're willing to put in a ton of time to learn how to tune these things yourself, a pre-made tune is probably the cheapest and easiest way out for you. You can try taking it to a local shop to have a custom tune done, but I have always viewed those with skepticism. Anyone who says they can properly tune a car in an afternoon is full of it. It took a whole team of GM engineers months of testing, trial and error, and math to make the stock cobalt run well. Do you think Tuner Bro's tune shop across town can outdo GM engineers in an afternoon? I don't. But ZZP (or OTTP, or another big ecotec shop) can probably come close.

 

[YoungGun]

Assuming the car is in good running condition (no intake leaks, no codes, etc)....I think my next step if I were you would be to contact ZZP, and see if they have a canned tune that would work with your setup.

That's probably blasphemy to some on these forums who tune their own cars. And I understand their logic; a canned tune isn't the "best" tune for anyone. It's a compromise to try to make a single tune work for a bunch of different cars so ZZP can make money. But what a canned tune does well, is that it works for most people, under most conditions, most of the time, and it probably won't blow up your motor. And for most of us, that's good enough.

Unless you're willing to put in a ton of time to learn how to tune these things yourself, a pre-made tune is probably the cheapest and easiest way out for you. You can try taking it to a local shop to have a custom tune done, but I have always viewed those with skepticism. Anyone who says they can properly tune a car in an afternoon is full of it. It took a whole team of GM engineers months of testing, trial and error, and math to make the stock cobalt run well. Do you think Tuner Bro's tune shop across town can outdo GM engineers in an afternoon? I don't. But ZZP (or OTTP, or another big ecotec shop) can probably come close.

Great points. Thanks. I'm not certain there's no mechanical issues at play, however it's going to be costly figuring out either way I guess.

 

[Dale E]

So, have you talked to Jeremy and received any insight into this? Was it running okay for him? Did he ever notice this when he owned the car? What did he do to the tune himself or have someone else do? Is there a history of this with the car, or is this something new after you bought it? Did Jeremy just live with it or get used to it? I know he auto-crossed it and was on a few meet ups with the Goblin family.

@Ross, did Jeremy ever tell you his car was running this way?

The doctor can't help you fix this issue without having a full and accurate history of the symptoms.

Are all of your electrical connections secure? Did you trailer the car to your hose from Arkansas? Maybe you jarred something loose? Is the throttle position sensor built into the throttle body on the Cobalt? Like my Enclave they want you to replace the whole throttle body if the TPS goes bad! Does the Cobalt have a idle valve solenoid? The rubber tip on the one in my Cadillac would get stuck with oil and carbon and would have to be cleaned now and then or it would idle bad or die.

One transposed number in one table will kill your ride and the hunt finding it may be long. Kind of like all the knackered electrical problems that keep arising with these builds.

I've got a 2011 Buick Enclave that the tach is twitchy all the time - worse on acceleration and going up an upgrade/hill. The factory put on whacked out throttle bodies and did a recall. Then it has a 6 speed electrically operated transaxle that hunts for gears all the time which causes the engine to surge and the tach twitches with this too. Hate computerized car stuff!!

Enjoy your new ride and learn it well!!

Dale

 

[Gtstorey]

You need to check for DTC codes even if you don't have a check engine light, since some important ones may have been turned off in the tune. Second, it will help if you can pull a data log with it running so you can start to see what is going on.

 

[YoungGun]

So, have you talked to Jeremy and received any insight into this? Was it running okay for him? Did he ever notice this when he owned the car? What did he do to the tune himself or have someone else do? Is there a history of this with the car, or is this something new after you bought it? Did Jeremy just live with it or get used to it? I know he auto-crossed it and was on a few meet ups with the Goblin family.

@Ross, did Jeremy ever tell you his car was running this way?

The doctor can't help you fix this issue without having a full and accurate history of the symptoms.

Are all of your electrical connections secure? Did you trailer the car to your hose from Arkansas? Maybe you jarred something loose? Is the throttle position sensor built into the throttle body on the Cobalt? Like my Enclave they want you to replace the whole throttle body if the TPS goes bad! Does the Cobalt have a idle valve solenoid? The rubber tip on the one in my Cadillac would get stuck with oil and carbon and would have to be cleaned now and then or it would idle bad or die.

One transposed number in one table will kill your ride and the hunt finding it may be long. Kind of like all the knackered electrical problems that keep arising with these builds.

I've got a 2011 Buick Enclave that the tach is twitchy all the time - worse on acceleration and going up an upgrade/hill. The factory put on whacked out throttle bodies and did a recall. Then it has a 6 speed electrically operated transaxle that hunts for gears all the time which causes the engine to surge and the tach twitches with this too. Hate computerized car stuff!!

Enjoy your new ride and learn it well!!

Dale

I asked him about it and he said he didn't have these stall/RPM fluctuation issues. He said in the past year he only took the goblin out once to autocross and then another time around town just before trailering to my house. I guess he had no issues. When we test drove it a couple times at my house I wasn't sitting around at a stopsign or stoplight but besides the touchy throttle/possible RPM fluctuations it didn't have issues. It seems like the issue really starts to present itself if you're doing lots of accelerations and abrupt full stops. Even revving while in neutral sometimes it is stable, however i'm not really getting higher than 2K rpm. I think the times it does start surging/stalling it's after deceleration to a stop after 3K or higher RPM.

The only thing he mentioned was to clean the throttle body which I completed with no effect.

I believe it was tuned by a local guy called Tuned by JP.

I checked the MAP, MAF sensors as well as the other connection points I could find. The vehicle was trailored to my house, yes. The throttle position sensor is not built into the throttle body, so I guess that's good. I think it has a Idle Air Control Valve, i'll check the hose on it.

Unfortunately I bought a scanner and now I can't find it so I need to get a new one.

Thanks for the help!

 

[Gtstorey]

What RPM is it trying to idle at?

By "lost" scanner I hope you mean code reader. The scanners that are really going to be helpful are expensive enough that you likely won't lose it.

I looked up "Tuned by JP" and it looks like it's a LS based company. Maybe the LSJ ecm's or similar enough to the LS stuff for them to be able to do a good job? From what I have read you don't want an LS tuner trying to tune a LNF without the tuner doing a lot of research.

 

[YoungGun]

What RPM is it trying to idle at?

By "lost" scanner I hope you mean code reader. The scanners that are really going to be helpful are expensive enough that you likely won't lose it.

I looked up "Tuned by JP" and it looks like it's a LS based company. Maybe the LSJ ecm's or similar enough to the LS stuff for them to be able to do a good job? From what I have read you don't want an LS tuner trying to tune a LNF without the tuner doing a lot of research.

Haha yah I meant code reader, the Amazon one.

It will idle at 800-1000. Little higher on initial start then drops down a bit gradually. I think thats normal. With the proper prodding of the gas pedal it can either flutter and die as soon as I come to a stop, or it will wildly surge from hundreds to over 2K over and over and over. Sounds like im 16 and obnoxiously revving my engine nonstop, but my foot is completely off pedals and in neutral.