X loves the cold, hates it warm
 

I have been battling a particular issue for about 8K miles now and can't figure it out. I searched on here for a similar issue but no luck.

When it is cold outside (below 50 degrees), my X runs almost perfect. It will stumble at idle a few times at start-up and a few times at the beginning of take off from stop, but otherwise it will accelerate and cruise with no stumble and no SES light.

When it is warm outside (between 50 and 70 degrees), more stumbling at idle and take off and an intermitent SES light.

When it is hot outside (over 70 degrees), rediculous stumbling at idle and take off and constant SES light. The hotter it gets outside the worse it gets to the point where the stumbling will shake the entire vehicle constantly and will hamper acceleration to the likes of a really fast bicycler. The only way I can get it to stop is to turn it off and restart it.

I have pulled the codes in hot weather and get the non-specific misfire code. I've been putting off fixing it since it has been so cold but it is about to get warm again and it will be a pain to drive.

I have checked the DISA valve, it's fine. I don't believe I have an intake leak, none seen. I was thinking O2 or MAF because of the effect of outside temperature but I don't like playing part roulette. Anyone heard of this before?

Part roulette or not, I think the MAF would be a good starting point. Cleaning them is pointless. Do you have an aftermarket intake or filter? If you've got a misfire on all cylinders, random ones, or just one bank (1-3, 4-6) would be helpful information for helping to diagnose the problem.

Intake and filter are OEM, P0300 is the code I get which from what I could find out about it is a random misfire.

I just recently got back from NTB for an alignment check and they gratuitously pulled the codes because it is warm today and SES Light is on and they told me I have a vacuum leak. I asked for more info like where is it leaking from and they could not tell me. They asked if they could charge me $88 to hook it up to the smog maching. This didn't sound too bad to me but I wanted to report back to the forum for what you guys might think a good place to look first would be or if this sounds reasonable. I'm also going to do a search on the forum for vacuum leak culprit areas.

Any ideas are greatly appreciated!

$88 is a bit steep for something that literally takes 10 minutes tops (I have one), but I guess it is what it is.

I have had similar problems on older cars (different make) back in the day and it was due to a vacuum leak.

Thanks guys! I'm going to give it a good looksee. If I can't see anything, I'll start replacing hoses until it starts running right . . . starting with the cheap ones first of course. Hopefully Vineyard wants to buy it, he's looking for a 3.0 sport and I'm getting tired of working on this thing.

At least replacing hoses is cheap, and isn't really a waste either. You've got low mileage, but it's also 7yrs old, so it's can't hurt.

Leaning towards the MAF myself.... if ambient temp is the only change that gets you a fault.

I was thinking MAF too for the same reason but like m5james said the hoses are a cheaper place to start. I'll knock it out this weekend and report back. Hopefully this thread will help someone else out down the road.

You just gonna replace the hoses and skip the smoke test all together? For the cost and small amount of time it'll take, doing the hoses won't hurt regardless. I had a lingering misfire on my 7, and eventually found it on a brakebooster line, and inside of one of the Z folds, the inner corner had a hairline split that came wideopen once I pulled the line of. Good luck and keep us posted.