Let me preface this with the fact that I have already searched the forum, albeit on my phone (so it limits results) and through the solutions suggested there, I've replaced my TPS and my IAC Valve.

Being stationed here in CO, I am experiencing an issue that I have never had before - when the temperature drops below roughly 32 degrees, the car was idle surging REALLY bad - from 400-1700, and then dying off as it was unable to keep itself running. After about ten minutes of trying to hold it at about 1000 RPM which is really ******* hard in boots while you're freezing your *** off and it's trying to jump idle (my neighbors hate me at 0445 AM), it warms up ENOUGH (the indicator moves across the 1 in 100 on my temp) for the idle to hold at about 800 RPM - which is normal. It did this **** last winter too but it was snowing so bad most days I didn't even do anything except start the car and then catch a ride to work with a friend.

Since it was idle surging, I figured, hey, maybe the IAC valve has **** itself. I replaced that last night - it was pretty foul, and probably stood to be replaced, or at the very least cleaned, but this morning when I started the car, it replaced surging from 400-1700 to surging once and then straight dying. I had to manually hold idle down again, which just made it sound like it was idle surging and still pissed off my neighbors.

So now, having replaced the TPS and IAC, I'm lost. If it were the MAF the car wouldn't want to run at all, or so I assume. The last time I had a MAF go bad it didn't even want to start. Once the car is warm, it runs fine. If it's above 40 and doesn't drop, it starts fine/runs fine. Like, really, replacing the TPS/IAC probably didn't hurt anything and if anything it's operating a little more smoothly on the backside than it was before, but this zero-dark-thirty revving match I have to do every morning is about to cause a divorce because my husband is a Mustang guy and all I keep hearing when I try to trouble-shoot is "hahaha try setting it on fire".

The car is more or less stock - SLP intake, bullshit not worth mentioning exhaust, and like, some free mods. It's daily driven, high miles, upkept well enough. No tuning worth mentioning either, so a lot of the threads I read with this issue didn't have solutions that I could even work with (IE taking it back to my local shop, which I don't have to have them adjust a tune they didn't do). Please HELP. I'm about to drive it onto my airfield and land a Chinook on it.

 

Problem #1. We'll come back to that, later...


This is the point where your PCM switches from Open Loop (calculating Fuel/Air without O2 sensor feedback) to Closed Loop (calculating Fuel/Air off the O2 sensor output) operation.

During Open Loop, your PCM is going to rely on inputs from your air sensors to figure out the density, temperature, and flow of air in to the engine and then add fuel based on that.

Since this problem doesn't happen when the weather is warm and your PCM seems to be switching from open to closed loop properly, I think you can assume your fuel delivery system is fine and coolant temp sensor is good. That leaves the MAF, IAT, and MAP sensor. If you have an engine scanner, you can easily check the values for these and compare them with baseline values or what they should be. (IAT is easy - it should be close to the outside air temperature.)

I've had a MAP sensor go bad on me, but I got a check engine code for that one.

The MAF sensor can get dirty. When this happens, it misreads the amount of air going in to the engine and cuts fuel. (If you are at altitude, I'd think this effect could be amplified.)

SLP Lids often come with K&N air filters. K&N air filters are PURE EVIL and cover the MAF with a layer of oil that fouls them. (I learned this the hard way and almost sold my car in frustration before I fixed the problem.) Good news - a $5 can of MAF cleaner often solves the problem. Do you have a K&N or other oiled air filter under your lid?

 

Check the intake bolts, probably loose and will make it surge terrible cold.