I have been diagnosing this problem for quite a while now and it has finally gotten cold enough here in SC for me to be pretty sure about this problem. Two days ago it was 65 degrees and sunny, the car idled rough, the shifter vibrated enough to shake your arm and I could feel vibration when putting my hand half on teh strut tower brace and half on the top of the intake manifold. It idled like this regardless of the temp of the car (160-215). Well last night it got down into the 30's here and I checked the car again. Vibration was BARELY noticable in the shifter and when checking the engine with my hand like before, you could hardly tell the motor was running (nice and smooth). I also checked this from 160-215 degrees, no change. So, what do yall think, what could cause a rough idle that is dependent on outside temperature only?

 

My car does the same thing, just not as bad as yours. My take: i have heard that there can be a micro fracture in the spark plug wire casing casuing a possible tiny arcing of the wire (i have heard of this, but no one ever said they had it happen to em), 2. The intake charge is cooler, so the computer somehow adapts to this. 3. the internal clearances of the opti change so the actual rotor makes a better spark transfer (i know metal expands when heated but who knows, people who replaced "good" functional optis for a new one said it really idles smooth), and 4. Only god knows why When someone else finds out plz post.

 

ever tried making sure you air intake temp sensor is clean and good?

 

I was thinking that might be the problem, but I havent had time to meter it and check. I also wasnt sure if a bad IAT could cause a rough idle, are you saying it can?

 

ttt

 

I have had the same issue. Try disconecting the IAT sensor and inserting a 4.7k resistor (available at radio shack). I just put it right into the connector and taped it up. Seems to run smoother and supposed to pick up a couple of horsepower. High octane gas is recommended with this mod.

 

Hmm, what exactly does this "mod" do? Sounds sketchy to me.

 

I noticed on the scanner one my IAT temp reaches 55-70 degrees the idle get a little less smooth. If you look at the spark advance it gets more erratic (for lack of a better word) and probably is being used to keep the idle steady. Since the IAT supposedly affects timing boom- that is my theory

I moved my IAT to a different position yesterday (w/ that dang jet kit: didnt want to hack the stock wiring) and it seemed to help, but it still heaksoak after sitting. I moved it to the old airbox location, before my CAI.