Car wanting to stall on cold start

[fstm5]

I've made a post about this before but I never really got around to showing what this was actually like and never got a solution


So I'm gonna try again

Ever since I cleaned my MAF's and got downpipes installed, my car started doing this

[IMG]https://streamable.com/hpj9f1[/IMG]

https://streamable.com/hpj9f1

This video shows it best although at times it actually stalls out

I don't tap the throttle, I know it seems like I did but I didn't that's just the car correcting itself

Any insight on this ? If anyones experienced similar issues? This only happens on cold starts


Car is on a stock map

[M5_Raz]

Didn't you say you'd buy new maf sensors?

[fstm5]

Originally Posted by M5_Raz

Didn't you say you'd buy new maf sensors?

Yes, tried that made no difference

[M5_Raz]

Damn. Are you sure you put the o2 sensors on correctly?

[fstm5]

Originally Posted by M5_Raz

Damn. Are you sure you put the o2 sensors on correctly?

So I didn't actually do the install myself it was done at my Indy shop, but I did check the main two 02's that I can reach, I haven't looked at the ones on the lower side of the downpipe but I feel like a bad o2 installation or a bad o2 would throw a code no?

[M5_Raz]

You can reach and see the lower ones too. But yeah, you'd probably get a code. I'd take it in to a shop if it was mine.

[crazyinp]

So you are running catless down pipes I would assume. Did you get tune? On cold start car is running rich to warm up the cats as fast as possible to pass emission. If you removed the cats and didn't get tune I am not surprised you have an issue in cold start. Also, I am sure someone from Florida and California will post how they don't have this issue. both of those state don't really start their car in temp below 50F

[M5_Raz]

Nope, you don't need a tune for catless downpipes in these cars. I've ran it that way for a year before I modified my stock tune.

As for the weather, it's 70f in the video.

[fstm5]

Originally Posted by crazyinp

So you are running catless down pipes I would assume. Did you get tune? On cold start car is running rich to warm up the cats as fast as possible to pass emission. If you removed the cats and didn't get tune I am not surprised you have an issue in cold start. Also, I am sure someone from Florida and California will post how they don't have this issue. both of those state don't really start their car in temp below 50F

I can understand what you mean but that also doesn't make sense


Yes, running cats without a tune isn't the ideal way but at the same time that's only if the cars ecu knows there is no cats, as of now I don't have an engine light for the no cats so technically speaking the ecu thinks the cars the same as normal, but yes I did consider that a possibility that it's because it's not tuned

Also I do live in California so that doesn't really matter

It just astounds me that this only happens when I initially cold start the car after a full night, when I go to work and the car is off for 8 hours, it starts up just fine.

[fstm5]

Originally Posted by M5_Raz

You can reach and see the lower ones too. But yeah, you'd probably get a code. I'd take it in to a shop if it was mine.

It's a hassle of leaving it with them since this is my daily driver, I don't mind DIYing this and figuring it out myself I just don't want it to be something like injectors, but I feel it's more a sensor or a loose connection

[M5_Raz]

I know what you mean. You've checked the crank case ventilator hoses, intake connections, ecu connections (including the ground wires under the ecus), o2 sensors, and maf sensors?

That's pretty much all you touch when you install downpipes. Did the behavior change in any way when you got new mafs?

[fstm5]

Originally Posted by M5_Raz

I know what you mean. You've checked the crank case ventilator hoses, intake connections, ecu connections (including the ground wires under the ecus), o2 sensors, and maf sensors?

That's pretty much all you touch when you install downpipes. Did the behavior change in any way when you got new mafs?

I haven't looked very deep into the ground wires etc but everything seemed fine, I'll do another thorough check this weekend


Nope, but the funny thing is these problems began as soon as I cleaned the god damn MAF sensors that's what made me believe changing the MAF's would clear up the issue

I'll probably look more into the intake/maf area see if anything is off

[M5_Raz]

Check to make sure they're plugged in the right way, I think it can go both ways