funny you should say that, the same thought crossed my mind and I went to a reputable mobil station yesterday and filled up with premium. I always use premium, my car runs like crap if I don't, but at over four bucks a gallon in connecticut still I will seek out the cheapest premium I can find. of course, no difference, tho it does seems to be running a little smoother overall once it gets going. so this morning, I watched carefully.... after firing up with a mighty roar, rpms dropped down to nothing and it searched and hunted at very low rpm's for about 45 seconds, then like a switch flipping it smoothed right out and the RPM's jumped right up to 1100 and was running quite rich at this time, it sat there for about 15 or 20 seconds, then over the course of the next minute gradually dropped to normal idle.

 

Have you checked your air filter as well?

For the fuel, try adding 1/3 - 1/2 a can of Seafoam to the tank. It should neutralize any water in the system. Let it run through on a full tank. Skip the the treatment for the intake... can cause harm.

This all sounds familiar to me...

Have you tried cleaning the Idle Air control Valve? I think once I cleaned that it fixed things for me, and I used the seafoam cleaner. I like this video from Scotty:


Here's another quick video on youtube I found. I just cleaned the crap out of it with the aerosol seafoam spray.

 

I'll take a whack at it this weekend, tho I am not expecting much.... it just stinks of a sensor or vacuum or MAF problem, what with the running rich and throwing the 1178 code a while ago, but a clean IAC won't hurt one bit. When you were having your problem, did it start with a healthy roar as usual then start its sputtering, and eventually work its way out of it on its own ? once mine does that, I'm good until it cold soaks again overnight. Checked coolant temp sensor, that's fine

 

a damp and windy yet balmy me 61 degrees in Connecticut this morning. started, idled, and ran perfectly. I finally have this figured out - move to a warmer climate!

are there other sensors involved in setting the mixture based on ambient temperature, or is it only the coolant temperature sensor?

 

intake air temp sensor , also the fuel rail temp sensor.....you should get a scanner hooked up before you start throwing parts at it though....that would help to narrow it down

 

Trying to figure things out on my Disco today I tried to run the truck with the coolant temp sending unit unplugged, and the fuel rail temp sending unit unplugged when the motor was warm and it ran terrible and at a high speed. Maybe one of those sensors is making the computer assume the motor is warm when it is actually cold? just a thought..

 

Mine would start with a healthy roar, and then start sputtering... occasionally it would stall out while driving by sputtering as I came to a stop. Once I cleaned the IACV the issue disappeared immediately!

 

cleaned IAC real good, but nothing has changed. and the colder it gets in the mornings, the more difficult it is to get it to stay running, at least up until the point where it figures something out on its own, kicks the idle up to 1100, and runs it rich for a few minutes. it might be time to break down and buy an ultragauge

 

Another observation - if I get sick and tired of waiting for it to get it's sh*t together and just put it in gear while it's going through its almost-stalling / hunting exercise, the idle evens right out instantly, right where it's supposed to be. What the heck is that all about ???? There's gotta be some clues in here somewhere, just not seeing it !

 

Another observation.... this issue seems to be related to a particular temperature range. If it's in mid forties and above, no problem. Under that, hunting and stalling for the first minute first thing in the morning, then fine for the rest of the day.... unless it's ridiculously cold. Yesterday it was 19 when I started it up in the morning, today it was 14... Fired right up, set its idle to around 1300, then 1100, then down to 700 - 800, beautiful. No problem.