Hi guys, i am new to the thread but been viewing as guest on this site for a while and its been very helpfull. So just registered but i have a 99 STS w/ N* course and had car 3 years know pretty decent amount about it and cant seem to figure out why it has a rough idle when cold? especially weather changing now and its even rougher. it been like this a year now but living florida its usually always warm. I have no codes on the dash, seems to smooth out once it reaches full warm up, when ideling if i rev up to about 1500 RPM goes away. tends to feel like its running out of gas sort of when really cold. know its not plugs and wires since changed all them recently normal maintance. I think i have a guess but want to see what everyone thinks first.
Thanks guys-mike

 

New plugs and wires.....how about coils?

 

Well i think with coils it would be doing itthroughout all different stages of engine temperature/engine RPM. it would be present at any given time instead of when its just cold..?

There are no codes in the system,im going to check again right now actually but other wise people are telling me to have someone with the techII scan tool check it out and see it it sense something thats off

 

I say coils because that's what was wrong with mine, same sympytoms you describe no codes either. Cropped up at this time of year too back in 06. It's worth a check. Just look at the coil posts to see they are not rusted or otherwise corroded and that wires are set properly.

 

Ok thanks for input, i will check them at daylight tommorow. I have been thinking if not the coils could it possibly be of the following....Engine coolant temp sensor? Idle air control valve? least thinking MAF? Just curious never had bought coils but do they run for this type car? last time i looked i saw they were in sections of 4 i think 2 cylinders each pack correct? I will check them all, im guessing there each indiviualy replaceable right?

 

I never jump to the worst case scenarios first, often little things need attention and presto it's fixed. Coils are pricy though, I paid $89 CDN. You are right two cylinders per pack, they are individual in pairs and come off pretty easy, they are all attached to one large bracket bolted on the rear valve cover.

I don't think a bad idle can be attributed to the coolant temp sensor, the IAC would cause surging not rough idle, MAF probably more of a high speed issue.

When the car is cold the system is feeding it more gas, I mean here in Canada we rely onfast idle to keep our cars running in the morning this time of year. When the mixture is rich it seems to me that your ignition system can't deal with all the fuel so you get the roughness. Once it warms and leans out it gets better. I still think you are looking one or more of at plugs, wires, coils. Another possibility is a vac*** leak at the intake, bad hose, plenum gasket etc..

 

I just logged on to check the price and caught your post. The coils are sold seperatly correct? like 2-2-2-2 Guessing auto zone should carry? looking for rusty or corrision signs theywould be under the coil right, take it off and check and were plugs plug into them too right.(might not be a bad guess as i live off a salt water canal) and if was a va*** leak that could cause run rough cold and better warm

 

just found this info and pricing on ac delco pack. It looks to me that even thou there numbered there all same corect? this one pictured doesnt have any cylinder numbers on it
http://www.autopartswarehouse.com/de...9QQACD555.html

 

Yes only the factory OEM parts are numbered, they are all the same. Good idea to get AC Delco. If you do change a coil(s) good idea to get some dielectric grease. Might as well treat all wires and posts too.


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im thinking plug wire/plug also.... its funny though no codes???? 99stsguy, do you know how to pull codes? dont take affence
rickyd