ISX Horsepower/Torque setting

[TBraun]

I decided to buy this truck today. Engine sounds like it stumbles and possibly miss out at idle when cold. It did this when started the first time of the day. It's sounds much smoother when warm, but still might studder every once in awhile. Previous owner says it's bone this for a very long time. He recently had overhead run and made no difference. Any idea what could cause this? I haven't had a computer hooked to it yet, no engine warning light. Engine runs very smooth running down interstate. Put about 600 miles on it today just bobtailing, I can't complain how it runs down the road. Just don't know what to think about the low idle. It does sound better if you bump the idle up to 1000 or so. Don't hear anything abnormal out the exhaust. Engine has zero blowby, or next to zero. Appreciate any thoughts. Thanks.