cold weather = high idle!?

I have a 2007 mustang GT with JLT CAI and bama 91 oct tune. In Arizona I never had this problem but I am in Idaho right now and if the car sits a few hours outside in this 40'ish degree weather it goes like this.. when I start the car the tach shoots to like 3k+ and hangs for a few seconds before slowly idling down.

Anyone else have a similar issue? bama said need to change plugs.......

3k is a little high, but mine goes to 2K. Its normal.

Seems high, but yes if its cold it will idle higher and drop as it warms up. Like the old carb cars and chokes.

Mine does it too. I asked this very same question. It's ok is what I was told too.

I live in NJ and my 2v 4.6L E250 work vans when its cold out goes to like 2500 RPMs for about 20 seconds then comes back down. I have 3 of them and all 3 do that, they have done that since day 1 and all 3 now over 100k miles and still doing fine.

...it can be handled in the tune. Mine used to do that.

Mine to goes to around 2k+ right at start up then settles down 20 or so seconds later.
I'd think you want that to happen and it's on purpose to get oil around the engine the fastest right when she wakes up.
I wouldn't change it.

If I'm not mistaken, that is your PCM trying to heat up the O2 sensors. Would obviously take longer in cold weather. If it bothers you that much, you could have your tuner change the threshold in the tune, but then your O2s won't work as well (would probably affect fuel trims).

Mine goes a hair over 1k when its cold, then back down to around 800.

The stock tune limits idle to 2k. I wouldn't want it going any higher but that's me.

Normal, mine used to sit at 3500 or so.

When I had my bamma tune on I was seeing close to 2500 on start up

Mine does this as well.

I added a GT500 TB, Pypes offroad X and Violator mufflers and it was pretty bad. (2500+) Not to mention loud as Hell. I added a can tuned from SCT and now it's a lot better. I'm sure whenever I get a custom tune it'll be even better.

I have to revise what I posted, I don't pay attention to it too much but my car goes right to 1500rpm on a cold start and goes down after like 20 seconds.

never went to 2k or higher.

fdjizm said:

I have to revise what I posted, I don't pay attention to it too much but my car goes right to 1500rpm on a cold start and goes down after like 20 seconds.

never went to 2k or higher.

Click to expand...

That is totally normal. My car does the same exact thing.

Mine tachs up to close to 3K for a second or two on cold starts in cold weather. Pretty normal and doesn't worry me much (besides possibly angering my neigbors- but since my GT isn't a daily driver, it doesn't happen that often). Fuel tends to cling to metal and resist atomization when it's cold, so a little extra RPM helps the engine smoothly warm up.

Old cars with a choke used to deal with it by creating extra vacuum to more effectively suck fuel in when it was cold. New stuff compensates by raising idle via an IAC or electronic throttle body adjustment.

sounds like i shouldnt worry to much. IIRC it seems that the CEL might have flashed for a half second or so and the car sounded like it hit the rev limiter (around 3k).... this all happened very quickly but that is what worried me the most, but that's only happened once.

I think I will get the plugs replaced anyway the car has 50k on it.


Thanks for all the help and feedback!

I believe there is a cold start table that your tuner can play with if it bothers you.

I wouldnt rev it over 2.5k with a cold engine. Each metal expands at a diferent rate...