RPM searching and Stalling while coasting to a stop *SOLVED

[RazorGTP]

Need help with random stalling issue fellas.

This happened maybe 5 times all last year and now it happens at least once every time I take the car out. When I’m driving and push the clutch in And brake coming to a stop the car searches for idle and on the 2nd-4th drop in rpm it stalls.

I caught it on a datalog and sent it to Lund and this was the response:
“This runs rich to the point it stalls the car but airflow is reading we have an influx of air skewing the reading.”

I tried plugging the ram air tube to see if it was possibly a turbulence issue and also cleaned the maf. Lund then asked for me to try the stock Cai and TB so he sent me a tune and no difference. I datalogged another stall and this was the responses:

“Your log shows a very odd result to say the least. You let off the throttle here and the throttle blade closes all while spark stays roughly the same and even airflow decreases but yet RPM climbs. This should never be the case here. “

“Sounds like we have an issue here. The tune I sent you is for a stock car and fueling up to this is super lean and not going into coasting fuel shut off here. Some thing isn't adding up because the tune I sent you here is the calibration he have on our GT500 when it was stock. If the car was stalling before and then it started happening more often what changed on the car? At this point we need to have the car diagnosed by a professional mechanic because out of hundreds of other GT500's with the same exact mods your's is the only one having this issue. We've ruled out the intake as well as the throttle body so you're right it isn't these items causing our issue. ”

Not turbulence, CAI or TB...

Any ideas??

 

[SCGallo2]

Are you datalogging Engine Coolant Temp (ECT)? Just curious if it is stable under 200*F, depending on the t-stat and fan settings you are using, when the stall occurs?

 

[RazorGTP]

Are you datalogging Engine Coolant Temp (ECT)? Just curious if it is stable under 200*F, depending on the t-stat and fan settings you are using, when the stall occurs?

Yup, happens at all temps.. 150-190 so far. Have a 170 Tstat and vmp he so temps never break 190.

 

[biminiLX]

How about letting the car coast down in gear vs letting it coast in neutral or clutch in?
Does it do it in that scenario?
What is your TB/CAI combo?
-J

 

[RazorGTP]

How about letting the car coast down in gear vs letting it coast in neutral or clutch in?
Does it do it in that scenario?
What is your TB/CAI combo?
-J

No it’s only coasting in neutral. Jlt123 and cj mono but we already ruled out it’s not the Cai and Tb. Tried returning to stock with same issue and the logs show the air is fine.

 

[Catmonkey]

Have you checked for any diagnostic codes?

 

[RazorGTP]

Have you checked for any diagnostic codes?

Yup. Jon Lund II is stumped. I’m going to try new
Front O2s, it’s a stretch.

 

[98 svt]

Yup. Jon Lund II is stumped. I’m going to try new
Front O2s, it’s a stretch.

Funny, I was just going to suggest O2 sensors.

 

[biminiLX]

Easy, don't coast in neutral.
Swap O2s and then find a long down grade on highway and coast and see if gone.
Around town I'd think you could drive around it, I don't coast in neutral much I guess.
-J

 

[RILIE500]

do you have any header leaks ????..... on decel they will suck in air more o2........ sounds like exactly what car is doing .
trying to richen car for extra o2 from leaks .... like being described here.
i really doubt the o2s are bad if they logging correctly at cruise speed

 

[96gt02]

Ever consider switching tuners? Every-time I hear of someone with this problem they almost exclusively are Lund tuned

 

[07 Black Beauty]

My 07 Shelby with the same TB & CAI did this. I took it to Power by the Hour a couple of times and they could never find the cause. I was ready to sell the tb when Lund eventually got it worked out in the tune.

 

[RazorGTP]

Funny, I was just going to suggest O2 sensors.

It was just a thought I had but not sure why it wouldn’t throw a code or still idle, drive and wot fine.

Easy, don't coast in neutral.
Swap O2s and then find a long down grade on highway and coast and see if gone.
Around town I'd think you could drive around it, I don't coast in neutral much I guess.
-J

No no, by coast in neutral I mean when coming to a stoplight, throw it in neutral while braking after downshifting. Lol

do you have any header leaks ????..... on decel they will suck in air more o2........ sounds like exactly what car is doing .
trying to richen car for extra o2 from leaks .... like being described here.
i really doubt the o2s are bad if they logging correctly at cruise speed

I don’t hear any header leaks. I know my last terminator had a header leak a few times and it was very noticeable. Is your leak pretty auditable? Ya I’m not betting the farm it’s my o2s but running out of ideas so will try.

Ever consider switching tuners? Every-time I hear of someone with this problem they almost exclusively are Lund tuned

No Lund knows his shit and he has always took good care of me. What you mean you hear about multiple people with my same problem? Not Cai/Tb related?

My 07 Shelby with the same TB & CAI did this. I took it to Power by the Hour a couple of times and they could never find the cause. I was ready to sell the tb when Lund eventually got it worked out in the tune.

. Nice glad too hear.... Ya it’s not my Cai/TB 100%

 

[2011 gtcs]

Sounds like you just have air that's not getting metered correctly. Maybe a small vacuum leak?

 

[RazorGTP]

Sounds like you just have air that's not getting metered correctly. Maybe a small vacuum leak?

Possibly, how to find out?

 

[2011 gtcs]

Possibly, how to find out?

A smoke tester is a great option, or you can spray Brake cleaner around any area that could have a leak and look for a RPM jump. Make sure your T/B gasket is in good condition. It's odd you aren't getting a CEL from the car stalling out.

 

[96gt02]

Yeah my bet is either a vacuum leak or a tuning issue, and yes it seems like several times a week I see people tuned by Lund having very similar issues to you (mostly coyotes because there is so many more of them) but I have seen a handful of GT500s as well, they dont seem to be quite as bad as your issues though. Most people are just having issues coasting in neutral with the RPMs searching and bouncing real low but rarely do they actually stall from it, just get to the point of almost stalling. So maybe your issue is a combo of a leak and tune issue since its worse then most. Also if you already put the TB and CAI back to stock, why not throw the stock tune back on it (Yes you will probably get a CEL for the exhaust but it wont affect the car running) and see if the problem magically goes away, then you know its the tune?

 

[RazorGTP]

Well I just changed the o2s, did a Kam reset and Idle re-learn.... Same issue.

A smoke tester is a great option, or you can spray Brake cleaner around any area that could have a leak and look for a RPM jump. Make sure your T/B gasket is in good condition. It's odd you aren't getting a CEL from the car stalling out.

Well I don’t have access to a smoke tester but can try with Brake clean, the Tb gasket looks in good shape. Thanks. Yes I know it’s very odd.

Yeah my bet is either a vacuum leak or a tuning issue, and yes it seems like several times a week I see people tuned by Lund having very similar issues to you (mostly coyotes because there is so many more of them) but I have seen a handful of GT500s as well, they dont seem to be quite as bad as your issues though. Most people are just having issues coasting in neutral with the RPMs searching and bouncing real low but rarely do they actually stall from it, just get to the point of almost stalling. So maybe your issue is a combo of a leak and tune issue since its worse then most. Also if you already put the TB and CAI back to stock, why not throw the stock tune back on it (Yes you will probably get a CEL for the exhaust but it wont affect the car running) and see if the problem magically goes away, then you know its the tune?

I’m back and forth with Jon Jr right now trying different things... he’s going to play with the tune to see.
Hmm well I can try returning to stock and see I suppose... I have a 10%od and different lighter flywheel though eh, not sure if I can use a stock tune?

 

[98 svt]

Yeah, gotta be a vacuum/exhaust leak before those 02 man. Not sure what else it could be.

 

[biminiLX]

Sounds like a good reason to upgrade to an XBA elbow, 168KB and 148 JLT.
Add some power and it's one of Lunds preferred combos.
I know it doesn't fix the current problem, but just a good reason to add more power
-J