2015 mustang gt idle issue

[Nathan5150]

Hello all, I’ve been fighting an issue with my stang for over a year and after countless hours and searching I can’t seem to find a solid solution to my problem.

Car: 2015 mustang GT

Mod list:
Paxton 2200sl
3.33 pulley
2018 intake manifold (locked out)
Id1050x injectors
Long tube headers catless
NGK 6510s plugs gap .030
Beefcake racing torque booster kit
Maxflox rave BOV
Jlt intake
Ford performance vct solenoids
Vmp BAP
DSS one piece aluminum drive shaft
Lethal performance hdx clutch
DSS 1500+hp axles
Steeda rear IRS stop the hop kit
Weld laguna bead lock rears with Mickey Thompson et s/s
Weld laguna front with nitto g2s
Barton short throw shifter
Drive shaft safety loop
Trans bushing kit
Stock MT82
Billet OPG/crank
91 octane tune from Ortiz performance
Graham’s throttle body with spacer
Reische 170 thermostat
720RWHP 658ftlbs torque
*probably missing some

issue:
After driving vehicle for about a year on this setup 2000 miles total, I have ran into an idle issue. When the vehicle first starts idle holds perfect along with afr vaccum etc. When car warms up the idle will hold at 850-900ish then drop down to around 500rpms and then jump back up and continue to do so while at idle. Under throttle in gear car runs perfect doesn’t stall or die. But when returning to idle the issue persists. I will at times get a random/multiple misfire code. I clear it and drive on for a few days/weeks and it won’t return but still will have idle issue. I have tried 2 different tuners both local and an etune nothing corrected. I have replaced VCT solenoids, spark plugs, changed oils, different fuel stations, octane boosters, vaccum leak test, replaced egr swapped to stock throttle body and back to aftermarket one, cleaned maf sensor, changed battery, did compression test, performed kam reset/crank relearn etc. I’m over throwing parts at it and don’t have a local shop that’s worth a crap to take it to for help. Have also noticed at times under light throttle in 3rd gear around 3400-3500rpms out of boost if I WOT vehicle will hesitate for a second then hold power. Vehicle will launch fine run down the strip fine with no buck smooth as can be but idle like shit in my opinion. I have a return style stage 2 dual pump fuel system on order to install for e85 but am trying to cut this issue out before install. Vehicle is located in lovely Colorado at an altitude of 4600ft car has ran 11.2 @122 launching at 1500 rpms but I’m shooting for 10s this year. I’m stumped and it’s making me insane lol. Any help is appreciated I apologize for the long post but I want to give as much info possible for those who read it and may have similar issues or have insight.

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[KingKona]

You really expect someone to diagnose your heavily modded car on a forum?

If it was stock, and a known issue, that would be one thing.

 

[Nathan5150]

You really expect someone to diagnose your heavily modded car on a forum?

If it was stock, and a known issue, that would be one thing.

just trying to see if anyone with a similar common setup has had similar issues looking for insight. That’s the purpose of forums a community of people with similar cars, mods, problems etc to help one another. Do I expect to get a fix or a proper diagnostic? No but if I gain some more knowledge and find the issue maybe later down the road someone will run into the same concern and have a post to refer to. Appreciate the concern and response just not following the reasoning?

 

[KingKona]

just trying to see if anyone with a similar common setup has had similar issues looking for insight. That’s the purpose of forums a community of people with similar cars, mods, problems etc to help one another. Do I expect to get a fix or a proper diagnostic? No but if I gain some more knowledge and find the issue maybe later down the road someone will run into the same concern and have a post to refer to. Appreciate the concern and response just not following the reasoning?

It's just not a "common setup".

I would be looking for un-metered air getting in, and/or an issue with the intake manifold. They tend to break/crack where the sliders are.

 

[KingKona]

I had a 2016 GT, and the intake cracked where the mechanism for sliding the pistons for the...whatevers are. It was throwing misfire codes and demanding a relearn of the crank-position sensor.

It's a well-known issue.

With everything you've done, your intake manifold has been beaten on.

 

[Nathan5150]

It's just not a "common setup".

I would be looking for un-metered air getting in, and/or an issue with the intake manifold. They tend to break/crack where the sliders are.

I’ll try and take a look anyway to simply test that or is it just remove and inspect more or less?

 

[KingKona]

I’ll try and take a look anyway to simply test that or is it just remove and inspect more or less?

I think just remove and inspect.

It's is a known issue. Not that it's necessarily your issue, and I've done a horrible job of describing the issue, but the intake manifolds crack where some pistons move back and forth internally, and it creates misfire codes.

Might not even be visible externally.

There may be a TSB for it, you could check that part of this forum.

 

[Nathan5150]

I think just remove and inspect.

It's is a known issue. Not that it's necessarily your issue, and I've done a horrible job of describing the issue, but the intake manifolds crack where some pistons move back and forth internally, and it creates misfire codes.

Might not even be visible externally.

There may be a TSB for it, you could check that part of this forum.

I have a new in box manifold I may just try and swap out and see was wondering if I did the ol carb cleaner trick to see if I spray around it idle changes

 

[KingKona]

I have a new in box manifold I may just try and swap out and see was wondering if I did the ol carb cleaner trick to see if I spray around it idle changes

I don't think the carb cleaner thing will work. I'd just change it out, being sure to also replace the gaskets.

 

[Nathan5150]

I don't think the carb cleaner thing will work. I'd just change it out, being sure to also replace the gaskets.

Well replaced it still has slight idle fluctuations starting to wonder if a retune is necessary or possible stock fuel pump issue?

 

[Torinate]

My own thoughts would be to try a stock throttle body without the spacer. Also I’d be looking for any possible air leak after the MAF. I would also clean the the MAF and check / change the plugs. Start easy and worker forward into the tougher stuff.

Good luck.

Crap. Never mind. Already did that. I reread your post...

 

[Cobra Jet]

Since you have swapped out the intake and did most of the other known diagnosis/cleaning, I would check the crank sensor.

A faulty crank sensor OR the harness/connectors to it is another known culprit on the Coyote 5.0 that will throw misfire codes and cause idle issues.

Other M6G members have found that even just a stand alone P0300 was related to a faulty crank sensor. This could be your issue too, so review each thread carefully because each owner came across it in a different manner.

Check this thread:
https://www.mustang6g.com/forums/threads/misfire-at-high-rpm.174380/#post-3531453

AND this one:
https://www.mustang6g.com/forums/th...e-sensor-tone-ring.156234/page-2#post-3197692

——

I would pull the crank sensor first and see what condition it, the connector and harness are in.

--

One other note with regards to the MAF sensor:
Just because physically it looks fine and it was "cleaned" doesn't mean the MAF sensor can be ruled out. The MAF sensor could still be failing and the only real way to know is by getting a voltmeter and actually testing it (or using other test equipment if at a shop). See this older thread:
https://www.mustang6g.com/forums/th...iple-maf-sensors-to-fail.140684/#post-2936515

 

[Cory S]

720whp on gasoline. Stock .009-.012" ring gaps don't like that. I'd be checking compression, and bore scoping the pistons.

 

[Nathan5150]

Since you have swapped out the intake and did most of the other known diagnosis/cleaning, I would check the crank sensor.

A faulty crank sensor OR the harness/connectors to it is another known culprit on the Coyote 5.0 that will throw misfire codes and cause idle issues.

Other M6G members have found that even just a stand alone P0300 was related to a faulty crank sensor. This could be your issue too, so review each thread carefully because each owner came across it in a different manner.

Check this thread:
https://www.mustang6g.com/forums/threads/misfire-at-high-rpm.174380/#post-3531453

AND this one:
https://www.mustang6g.com/forums/th...e-sensor-tone-ring.156234/page-2#post-3197692

——

I would pull the crank sensor first and see what condition it, the connector and harness are in.

--

One other note with regards to the MAF sensor:
Just because physically it looks fine and it was "cleaned" doesn't mean the MAF sensor can be ruled out. The MAF sensor could still be failing and the only real way to know is by getting a voltmeter and actually testing it (or using other test equipment if at a shop). See this older thread:
https://www.mustang6g.com/forums/th...iple-maf-sensors-to-fail.140684/#post-2936515

Thank you for the response I’ll definitely give that a try cheap enough part to replace and hope for a good turn out ! Will update when done parts look to be a bit out.

 

[Nathan5150]

720whp on gasoline. Stock .009-.012" ring gaps don't like that. I'd be checking compression, and bore scoping the pistons.

Have really hoped this wouldn’t be the case but will of course have to check and hope for the best, I guess worst case it’s a good excuse to tell the wife for going built. Will update once performed

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