Persistent cammed 01 cobra stalling issue

BrokeMedStudent

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Hey everyone,

I have a 2001 cobra 35k miles with some persistent idle problems. Previously, I had a full exhaust put in with NA cams, JLT intake, and accufab dual blade throttle body. It was tuned to 353 RWHP and everything was great...except now the car stalls at nearly every stop. What happens is, as I put the car in neutral and come to a complete stop the idle will typically drop a few hundred RPM and either die or rev back up to normal idle. The tuner said there is nothing they can do on their end and there must be a non-tune issue that needs to be resolved. They said the accufab throttle bodies can cause idle issues but I'm not convinced; the throttle isn't sticking and once the car does successfully hold idle it is dead set and smooth at 900 RPM. In addition, if I blip the throttle when in neutral the revs drop and the car dies every time. Here is what I've tried so far:
-Cleaned MAF, idle air controller, EGR (everything looked clean to start with)
-Replaced IAC with OEM unit (nothing changed)
-Cleaned intake filter
-Checked for vacuum leaks (there are none)
-Checked the air gap on the closed throttle body (looks perfect)
-Checked the throttle cable

Previously, before I had the cams installed, I had a shop replace some O2 sensors due to a code that has never come back. I'm not sure if the sensors were OEM or aftermarket and if that would make a difference.

Another bit of information: recently after I had a shop look into the idle tune (which they adjusted but the car still stalls) I got the car back and noticed that at high RPM at full throttle I'm losing power. I'm 99% sure it's not wheel spin and I don't think the clutch is slipping. Could the cool dense Arizona air be causing my MAF to max out? Is that even relevant?

At this point, I'm at a loss and was hoping someone with more experience could share their thoughts. Is it the tune, is it the O2 sensors, MAF, or something I'm just not thinking of?

Thank you!
 
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DSG2003Mach1

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Could be in the tune with dashpot decay or something but also aftermarket TBs on these cars are nightmares and usually not worth it

If you still have the stock TB I’d throw it on there for shits and giggles
 

BrokeMedStudent

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Could be in the tune with dashpot decay or something but also aftermarket TBs on these cars are nightmares and usually not worth it

If you still have the stock TB I’d throw it on there for shits and giggles
I'll have to read into the dashpot decay and bring that up with my tuner. If that's the issue hopefully I can keep the accufab TB on there. I did put OEM TB back on with the current tune and the car had a fast idle and died as soon as I tried to drive it lol. Thank you!
 

01yellercobra

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A lot of tuners don't bother setting up the TB. Most of the time they need some tweaking to get things right. Are you able to datalog?
 

BrokeMedStudent

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A lot of tuners don't bother setting up the TB. Most of the time they need some tweaking to get things right. Are you able to datalog?
I think a datalog is a good move. I can check in with the tuner and tell them everything I've tried, and maybe we can see what parameters are out of line when the engine dies. They seemed to really be fixated on the throttle body and tell me that it's not their problem so I might need to dig into them this time so we can get to the bottom of this.
 

01yellercobra

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The reason I asked if you can do it is you might need to adjust the throttle stop. I've found it easiest to do that while watching the IAC duty cycle on a datalog.
 

IronSnake

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I second the dashpot adder. Usually requires 1 to 2 tenths of a percent more in my experience.

Depending upon the tuning device/tables, they may need to also adjust engine state settings and the initial value that the IAC returns to when you come off throttle.

All things that greatly impact drivability.
 

Badaz01

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Subscribing to this. I’ve had idle issues since my build and the tuner pretty much said the same to me. I asked about the dash pot and adjusting the stop and he said I already did that. Cleaned and replaced all the usual idle valves etc…… Still not completely resolved. I have noticed the car idles better in 93 fuel as opposed to e85. I tried the old disconnect the negative terminal thing and it worked for about a day and a half then what ever is causing my idle issues the computer seems to relearn. Idk just my .02 cents.
 

hotcobra03

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I had issues at times stalling at a stop..

I had replaced all my coils for a jerk issue.

After I did notice the stalling had also stopped .

I never did get code for misfire
 

IronSnake

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Subscribing to this. I’ve had idle issues since my build and the tuner pretty much said the same to me. I asked about the dash pot and adjusting the stop and he said I already did that. Cleaned and replaced all the usual idle valves etc…… Still not completely resolved. I have noticed the car idles better in 93 fuel as opposed to e85. I tried the old disconnect the negative terminal thing and it worked for about a day and a half then what ever is causing my idle issues the computer seems to relearn. Idk just my .02 cents.

You can do an idle reset, which may mess with the IAC settings a little bit and require a tune fix up.

Best way to do this is get the car up to temp. Shut it off. Unplug the IAC. Start it up. You will likely have to peddle it. Go out to the TB and adjust the set screw to get the car to idle on the lower side of your desired idle. Shut the car off and plug the IAC in. Start it up and see how it does. If it does okay and idles down to where you want it, great, settings were close. If not a retune will be needed.

What's happening is your target idle in the tune may be 850. The set screw may be only able to support 600rpm without the IAC. You're requiring the iac to carry the motor 250 rpm to target, which makes it work a lot harder.

Whenever I build a new tune I start with no IAC help (IAC Off). Get the car warm. Set the idle screw to just below target idle. Then turn the IAC back on, adjust the PWM values as needed to get the car to target idle. Rev it, drive it, etc. Make sure idle comes down and maintains without dipping too hard or struggling to maintain

It's an art and a science.
 

DSG2003Mach1

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these cars can be a pain in the ass and I think some tuners just don't want to spend the time. My car with a stock TB didn't want to return to idle for shit, he spent a couple hours on the dyno dialing that in along with everything else (we were fighting some gremlins so every time he updated the tune after a pull he'd make changes to fix the drivability, I'd say it's about 98%).
 

BrokeMedStudent

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Update: I reloaded the original tune that was done after I had my cams installed as the most recent tune left my car dying on hard decelerations earlier today. This older tune is by the tuner that just told me my accufab TB was the issue. At the time I had the old IAC in and now that the IAC is replaced it comes back down to idle pretty well with a minor drop in revs. It still stalls when I quickly rev the car in neutral and take my foot off the gas. This leads me to believe there is a dashpot issue and/or maybe I need to adjust the throttle body. I have a break from school in a few weeks and I will start by checking the IAC duty cycle with some TB adjustments. If that doesn't work I'll see if I can get the dashpot adjusted. Thank you everyone for your replies!
 
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Roush6018

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hey i am trying to help the stalling issue. i understand you had it tuned when you installed exhaust,cams,intake and throttle body, then you say it was perfect, now you say its stalling unknown time later.

i would recommend do a compression test and leak-down test on all 8 cylinders with a warm engine and see if any of those results pass or fail.

these 2 tests can be done in 1 day and will give you an idea if the problem is in the motor or a problem with the air/fuel control. good luck, my 03 cobra makes some weird noises but it never stalls.
 

Badaz01

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Update: I reloaded the original tune that was done after I had my cams installed as the most recent tune left my car dying on hard decelerations earlier today. This older tune is by the tuner that just told me my accufab TB was the issue. At the time I had the old IAC in and now that the IAC is replaced it comes back down to idle pretty well with a minor drop in revs. It still stalls when I quickly rev the car in neutral and take my foot off the gas. This leads me to believe there is a dashpot issue and/or maybe I need to adjust the throttle body. I have a break from school in a few weeks and I will start by checking the IAC duty cycle with some TB adjustments. If that doesn't work I'll see if I can get the dashpot adjusted. Thank you everyone for your replies!
Maybe a coincidence or just different fuel type, but I switched to 93/torco for winter storage/the occasional fair weather around the block cruise to keep her lose. I was having similar issues when on e85 and when I switched fuels I changed the fuel filter to a stainless steel mesh filter. My idle since with 93/torco has been good no issues other than a smidge high. Can’t wait to try e85 in the spring. Just a suggestion don’t know how old your filter is or your fuel situation.
 

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