ScrappyCoco

Hey guys, new to the forum here. I've been having an issue with my mustang dying after starting it up, whether it's a cold start or its been running all day, heat doesn't seem to make a difference in symptoms. Oddly enough it varies differently on where I'm at. There is a gas station by my work that will die immediately every single time unless i give it a good amount of gas, but at home i almost never have problems with startups. This leads me to believe maybe being on an incline affects this? I have noticed it has more trouble when on an incline rather than a flat surface, but i may just be over-analyzing things. It started a few months ago and it isn't prominent on every startup, but at least 1-3 times a day. The reason I've decided to seek out help here, is because i have confirmed with Lund Racing that my tune is not the reasoning behind this as it's been running solid for 2 years with no issues and is just now within the past few months becoming an issue. Another interesting take that might give off a hint, is i also now have a check engine light (P0111) regarding a bad intake air temperature sensor. I've cleaned my filter, the MAF, and made sure everything is seated properly, and to no avail, i'm continuing to have the same issues.This issue starting happening way before the check engine light came up so i don't believe they are related but i could be wrong. I have always used premium gas, and have run Seafoam/Lucas multiple times since i've had the car. I do not neglect it in maintenance in any way. Please let me know your thoughts on this and if anyone is familiar with experiencing the same issue. Thanks!

DippinBob

Hey ScrappyCoco,

One thought is to check your Intake Manifold Runner Control. Mine just failed but my symptoms were CEL P0300, P0308. (See my post on my issue.) But in looking into the failing IMRC it does say that stalling or difficulty starting are symptoms.

https://www.yourmechanic.com/article...runner-control

Not sure if this helps but there are articles that talk about how to check for this failure without removing the intake manifold.

DB

pmcnutt

I have a 2015 GT with 27k miles. I just bought it about a month ago. It has a very rough start cold or hot but smooths out quickly. When I say rough, it goes from 1100 to 400 to 800 to 1500 to 750. Cycles about 3 times in this pattern. I checked MAF and cleaned it...that's not it. NO codes are being thrown, I checked with scannner I have...nuthin. It hasn't completely died like Scrappy's but it's not normal at all. Any ideas???

99GTvert

Is your car stock? It might have an aftermarket tune that might need work. You've had it a month so I'm guessing you've put in a couple new tanks of gas, right? What octane fuel (E85 by any chance)?

Does it drive smooth after the first 15 20 seconds? Does it idle weird when you stop at a red light/stop sign? How about when you pull into your parking spot?

pmcnutt

The only mod I can tell is Roush axle back exhaust. Everything else appears to be stock including air filter. I've tried 87,89 and 93 octanes...no difference at all between the 3 fuels. It only idles weird at start up...after that, it's smooth sailing with no issues. It's not as bad when its warm and you start it up but the problem is still there...about 50% of what it is at a cold start. Really odd. I bought the extended warranty when i bought the car that covers everything except normal wear/tear. I may take it back to dealer soon to let them diagnose.

pmcnutt

Both of us may just have a bad MAF or IAC. Have you ever replaced either?

99GTvert

Maybe the car has a tune on it, though I don't know how to check for that unless the dealership can figure that out.

Hopefully the dealer doesn't revert to "oh thats normal".

Random question but was the battery disconnected before you bought it? If it was disconnected then maybe it was trying to re-learn the idle though that wouldn't explain why it does not do that after the car starts up...if that warranty means you don't have to pay a penny to have them look at it (so no diagnostic fee) then I'd take it in. If there is actually a charge to look at it, then maybe try unhooking the negative battery terminal first, then hook it up again and start the car, let it idle for a few minutes. That shouldn't cost anything.

99GTvert

No, my 2012 hasn't had the issue though (its stock).

It would seem very strange for a 4 year old car to have those go bad unless water was sucked in or some other bull**** happened. Also if those were bad then it should have those symptoms beyond the initial startup (despite my post count, this is my educated guess only). They read the air and "report" it to the computer, but if its funky only on startup then I don't think those are the problem.

I would try a quick/simple fix before buying new parts though because that can get costly and frustrating. The dealership should be able to figure it out.

pmcnutt

I don't know if the batt has been disconnected before I bought it but I did it one time when i installed a trickle charge connector. It had the idle issue before and after. I've heard that tunes can cause the issue but I have no idea if mine has one or not. Yours sounds like you need to replace the IAT (or is that the same as the MAF??).

Roush05

My car used to struggle on startup once in a while and even die. Turns out my AC compressor was going bad and it went out on me while up in the mountains. I think the AC compressor is a fairly common thing to crap out on these cars so it might be worth checking into.