Hey guys, I've got a problem i've been trying to fix on my 08 GT for a while now (mods are in my signature). On cold days (less than 50 degrees), my engine sometimes (75% of the time) has an issue generating power on start up. When I crank, the engine starts normally but shortly thereafter starts to idle strangely. It most often happens when I put the car into gear. As the clutch catches, regardless of how much gas I give, the engine seems to struggle generating enough power to overcome the resistance of first gear. This happens for about 3-5 seconds before it figures it out and then drives normally. Additionally, sometimes, if I let it idle in neutral, the engine will start having trouble maintaining the ~700rpm idle. It will waiver from 500-900rpms and sound like its struggling to keep going.

At first I thought it was a clutch issue (before it ever started idling strangely in neutral) but there's no issue there. Then I figured it was a MAF, throttle body, air filter issue, but I cleaned all those and the problem remained the exact same after I cleaned all of them and reset the battery. Now I'm thinking maybe it's a fuel issue (with water vapor? or something?). Any ideas of what it could be or stories of similar experiences would be greatly appreciated, I looked around the forums but couldn't find anything that quite fit the bill. Thanks for your help!

 

Iac valve?

 

does not have an iac like older fords

 

Oops. Duh. My bad.... I can't see your mods. List them plz.

 

Sounds like it is lean. And probably has to do with your tune.

You might want to contact Tillman with the symptoms.

 

First I'd try re-flashing the tune , the adaptive memory can have some bad data in it for what ever reason , and re-flashing the tune will clear the memory so the computer relearns the idle data ...

 

1.) how many miles?
2.) Have you cleaned the throttle body?

 

36,000 miles, and I cleaned the throttle body about 1000 miles ago.

 

Thanks for the advice, I'll work the tune angle this week and see where it takes me.

 

Please keep us posted as I have the same issue!!

 

Any update? If you still haven't, I'd also say talk to Tillman. If anything, just to rule out the tune.

 

Kind of sounds like it could also be a vacuum leak. Check your vacuum hoses. The hose popped off my brake booster a couple months ago and the car kept stalling or getting ready to every time I took my foot off the gas. I could get it to idle, but it really felt like it was going to stall at any second. Under power in 2nd - 5th gear it was fine until i tried to coast in neutral, then it'd go back to acting like it was going to die, or sometimes it would. I popped the hood, saw the hose and reconnected it. It was back to normal after that. So, just something else to check out.

 

So I reloaded the tune, ran a batch of Chevron's Techron fuel system cleaner through the system, and have not experienced any problems since. Granted, it has been getting warmer and this problem does not surface as often when it's warmer out.

If I had to guess the root cause, I would guess a fuel system issue. As soon as I ran through the tank full of fuel system cleaner (about the time I made the original post), the car felt a lot better, not just on startup but for regular driving as well. Maybe I was expecting it to be better and artificially believed it, but the car hasn't had a strange idle since. I reloaded the tune about two weeks later (per the suggestions) just to make sure on that end and everything felt fine after that too. Hopefully that will help someone else too, thanks for all the suggestions!