Running Rich; A little rough.

Hey there,
I recently did the head gaskets on my 89 IROC, and upon completion, it runs good, but not like it used to. It's fine at high RPMs, but when it's at a low RPM, such as at idle or when it shifts into Overdrive at a high speed, it begins to run very rough - it just shakes. It also smells as if it's running too rich - quite a gassy smell.
Now, when it warms up, it gets a little better. (Not perfect though)
I know that when the car is cool, the computer bypasses certain things until it warms up and can control the air/fuel mixture that way.
So, my question is, could this be an adjusable problem, or does it sound more like a bad O2 sensor, (etc)?
Thanks!

-Matt
89 IROC

well at higher rpm's it goes into open loop, so i'm thinking MAF or O2 sensor. just a guess

how did you set the timing??? and are you sure that everything is plugged in??? as in O2 sensor, IAC valve, MAP sensor, and that none of these were damaged. if its just an idle problem i would start looking at the timing and the IAC valve. open loop is used when the car is warming up, so if it only does this cold then thats your problem, but if it still idels rough after say two or three minutes, and the car is at operating temp, then its nothing to do with open or closed loop. im thinking its more along the lines of a little gremlin you missed. a forgotten plug, something just slightly mis adjusted. a loose plug wire perhaps, the only thing i can really suggest is to go back and doubble check everything you disconected to do the job. make sure everything is securely snapped, screwed, bolted, or sealed.

Thanks for the quick replys!
I actually had the local Chevy dealer set the timing and make sure i hadn't missed anything when i had finished the project. They reported that the car is running up to par as far as connections, timing, etc.
Im thinking it's the IAC like you said. I'll play with it when i get off work.
Thanks again.

Iroc, you completely right about checking the IAC etc. but it does go into open loop about 3/4 throttle. dont know why but it does. i've found this out by trouble shooting problems in a case of a bad MAF and O2. it'll idle shittty but run beatuful when ya hammer it.

sorry, i really do hate taking these threads off topic but when the curiosity kicks in you gotta submit. someone wanna explain "open loop" ive heard it a lot and i think ive even used the term without fully understanding it...

open loop just an incomplete circuit. instead of making a "full loop" of all sensors then back to the ecm, certain ones get sort of by-passed and the engine runs off factory settings which are usually richer than needed. O2 is the main one, sometimes the MAF, IAT etc.