I've been noticing my car sputtering and making zero power when it is cold.

At this time I am not in boost and at maybe 5-10% throttle. It usually goes something like this:

Start car, pull out of garage, roll down driveway in 1st gear, pull out on to the street. Give it some throttle to accelerate and when the car reaches ~1500 RPM it just stumbles and sputters. It sounds like the hi boost Evos that break up top on stock ignition, but obviously I'm at 0 boost and just above idle for RPM.

Due to this sputtering, I end up shifting to 2nd, where it sputters again for a few seconds. By this time, I've reached a stop sign at the end of my street. When I accelerate away from this stop sign, these symptoms are gone

It only happens the first 20-30 seconds of starting the car...it is a minor annoyance but I want to make sure I'm not damaging/have damaged something.

 

You need to let the car warm up before driving it. Mine will sputter from time to time when cold also. I rarely drive it immediately after startin it up unless I'm in a rush.

 

its normal the car is just cold...mine does it too ur supposed to let it warm up but its ok if u just drive it out just low rpm until it is warm

 

definitely let the car warm up a while before you drive it. i always let mine warm up for a few minutes before i drive it.

 

I've always warmed up cars by driving them very easy until atleast the coolant is up to operating temp. Not sure why this car is any different.

 

forged pistons tend to expand/contract a little more than cast pistons do. so when the engine is cold, a forged piston isn't expanded and probrably doesn't seal in the cylinder quite as well as a cast piston does.

 

This is a stock motor Evo...I thought these pistons are cast...hence them splitting on so many people at ~350-400whp.

 

Not trying to jack your thread, but I have a very similar problem and some info to add.

First of all, I do let me car warm up, so that is not the issue. I can let it sit there for 5 minutes if I want and it will still do this same thing. It happens after the car has been sitting for an extended period of time (overnight or when I get in after work), but the rest of the time it's fine.

I have an XD-16 A/F gauge so I see what is happening, but I have no idea why...it goes extremely lean for those first 20-30 seconds of driving if you try to just give very light throttle...into the 18:1 A/F. I have to give it more gas than I want to just to keep it moving without "sputtering" and wanting to stall.

After about 30 seconds of driving this way, it is fine. Any ideas?

 

stock evo's have forged pistons i believe.
edit-actually, i think you're right. they are cast i think, don't know where i heard they were forged, must've heard wrong.

 

Hmm...I have the same wideband, but I haven't looked at the A/F readouts - usually concentrating on not getting rear ended since the car is making 0 horsepower. I will look tonight when I get home.

 

maybe i'm right about the forged pistons stock after all. in this article under performance. http://www.theautochannel.com/news/2...18/168969.html

 

Hellooooooooooo...Stock evo pistons are forged!!!You think you could run 23psi on a 4 banger with cast fricken pistons! WTF boys

 

The piston manufacturing process is really moot for this discussion because A) I doubt the pistons expand/contract enough to be causing a large enough blow by leakage for the sputtering we are experiencing, B) even if the expanding/contracting theory were true, there's no way it only takes 20-30 seconds for them to expand enough to stop this issue.

 

ive had the same problems. clean your maf sensor and let your car warm up 30-40 seconds and you shouldnt have any issues

 

well, seems like you have it all figured out then. sorry for trying to help. i'm glad i don't experience this cold sputtering since i listen to the owner's manual and let my car warm up before driving it. maybe if you do the same, you wouldn't have this problem.