lately ive noticed that my car doesn't idle up like it used to on cold start. it never bothered me to much because it wasn't an issue as hot as its been. it always started right up.

well fastfoward to some of our coolest days this year since last winter. was in the 50's this morning. i went to start the stang and it literally ran like dog **** on the first try. really rough idle around 500ish till it stalled itself out. it only lasted a few seconds, not enough to warm the engine up.

second start it fired right up and mostly fine, the tach was a just a smidgeon wobbly for about 15 seconds then all was normal, albeit at 1100rpm INSTEAD of the usual 1400-1500 cold start idle.

1100rpm is always the idle i get AFTER the engine is hot. but it most certainly wasn't hot yet this morning. i let it warm for a few minutes and drove off and all was well as far as i could tell.

edit: thought i should mention the car is bone stock except for an axle back. i am running 91 octane gas right now to take advantage of the "bullit tune". maybe i should go back to 87? but its been doing this for multiple fillups, its not like i just got into a bad batch all the sudden. its been this way for months.

but i really probably should get this fixed before it drops below freezing later this year. last thing i need is to come out on a freezing morning and find the car doesn't want to start.

 

sounds to me like the PCM is not getting an accurate reading of the
engine's temperature for whatever reasons. if you have an aeroforce
gauge, look at cylinder head temperature and see if it changes like
you would expect. if you don't have one, check the wires that run from
the engine wiring harness (on the passenger side) and route under
the intake manifold (and connect to the CHT sensor), for pinching/damage.

 

i looked earlier today and didn't see anything wrong under the hood at all. all the wires and hoses look fine. i inspected the ones off the harness on the passenger side as well and couldn't find anything wrong.

i mean its a fairly new car with only 12k miles on it. ive only had it a year, and ive owned it since new, all the dealer services etc, and only an axle back.

but this brings me to the next questions. first i noticed this switch under the hood on the passenger side that looks like its pressed down by the hood. what is that? (curious)

and secondly, this next question is probably more relevant to the issue. is the cooling fan on these cars 2010+ an always on fan? or is it supposed to come on at a set temperature. i know on my motorcycle that the fan only kicks on at a set temperature, otherwise it stays off. i would think the car would work the same, but i could be wrong?

because on this car, it hadn't been run for hours, engine was quite cool....i had the hood up and started the car and immediately noticed the cooling fan was already on. which brings me back to your original idea that the computer isn't reading temps right (ie: its stuck thinking its much hotter than it is).


edit: oh and while im NOT getting any warning lights....ie: check engine is it possible that its still throwing some codes?

seeing as the car is still under warranty im beginning to think it will be easiest just to take it to the dealer. i was hoping it was something simple and i could avoid a trip in and having to deal with them.

 

You're under warranty. Why try to self-diagnose it? I suspect a bad sensor somewhere.

 

Thats kinda my suspicion now after the feedback from hammeron and the symptoms.

i guess ill schedule a time to bring it into the dealer.

oh as for the why, i like to learn. im one of those people that doesn't want to just know whats wrong and can you fix it, i want to know how and why it works that way.

 

If you've got a good dealer, they will walk you through what they find, what caused the issue, how to avoid it (if it can be avoided) in the future, etc. The one time I needed warranty work on our old Escape before we traded it in, the tech even called me in before he replaced anything (like I asked for them to) to show me exactly what was causing problems, why, and what the new part was going to do to remedy it. Any good dealer/mechanic should do this. You're right, it's very important to learn and understand!

 

the switch may be for the active anti-theft option or maybe an aftermarket
alarm system.

with the factory tune, the fans come on at certain engine temperatures and go off when the engine temperature drops to a certain value.

i'm pretty sure the check engine light accompanies data trouble codes.

I'm like you and like to try and figure stuff out, but in this case without the ford service manual and maybe a volt-ohm-meter for testing, it would not be all that easy to troubleshoot. let us know what it turns out to be.....

 

ya so basically it seems the computer for whatever reason seems to think the engine is above that threshold which would explain why it runs like crappola when cold. makes sense, could be wiring or a sensor, or hell could even be the pcm for that matter. ill schedule a visit at the dealer and see what i find out. there hasn't been any check engine lights so i doubt any codes are being thrown. very likely a bad sensor.


update: service appointment is scheduled for wed morning at 8am to diagnose it. hoping for a quick and easy fix. even though the weathers nice enough for the motorcycle id rather not be without the car any longer than necessary.

 

lol just an update: they wanted the car left over night because there trying to replicate the cold start issue. (90 degree day, of course its gonna start fine). the question is will it be cold enough to cause the problem? today it was in 70's this morning and it started fine. last time i had problems starting was in the 50's. cold front comes in tonight, but will it get cold enough? we shall see.

i was told that the service tech working on my car had something he wanted to talk about to the guy i was dealing with, but won't find out what till tomorrow. so maybe he finally found something, or had an epiphany. i was also told that he was still going to be working on it tonight.

this raises the question, why continue working on it if you can't find anything wrong, unless he did and it was the thing he hadn't told the guy that was talking to me.

they said they are looking for another 10 gt because they don't know if the fan was supposed to be "always on". lol. also when i asked about how the cold idle was much lower than it used to be i was told in so many words that it was "normal".

ugh dealers. see why i asked here first?