my 22re had a rough idle only at warm-up. Thats is when I discovered low coolant level. I garage my truck and have never seen fluids on ground nor could find any evidence of external coolant leak. I assumed head gasket leak(coolant into combustion chamber) which would explain both coolant loss and rough idle. The head gasket looked OK. The timing chain cover had a hole where chain wore through. That would explain coolant loss. So what would cause rough idle at warm-up????