[QUOTE=iconoclast;572763]no codes at all. scanned every day last week. not one code just a rough idle.

That kind of thing can often be simple tune up stuff. Maybe a plug wire or two that are going bad. Either that or you could have a vacuum leak somewhere or a sticking idle air control valve. (or a number of other things)
I just had a truck with a rough idle come into the shop yesterday. In that case, the coolant temp sensor circuit was completely open. It was reading -40* on the scan tool. It was about 85* yesterday.
The best way to figure out what's going on is with live data on a scan tool.

 

Thanks, I only have VagCom which is mainly for VW/Audi vehicles however it has basic diagnostic scan and DTC/CEL readings for other marques. It has not picked up any error messages or codes so far for this vehicle.

 

Maybe something isn't quite right, but it's still within a certain tolerance. For instance, I put an aftermarket fuel pressure regulator in my GMC truck. It's not calibrated to hold the correct pressure. Which made the fuel trims go up to +20%. It idles a little rough due to low fuel pressure, but it doesn't have a check engine light. Now, if I got even a small vacuum leak, I'm sure it would come on because the threshold for lean codes on that truck is anything over 25%. Which is the top of the scale for long term fuel trims on that particular vehicle.
That's why live data is so important when it comes to diagnosing problems like this.

 

You should make the small investment in a ScanGaugeII or UltraGauge to monitor temps. Temp gauge on D2 doesn't move until close to OH. They also scan and clear codes as your present scanner does.
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I will look into that... Small price to pay for peace of mind. Thanks.