I thought I posted this earlier, but it didn't show up so I'll risk repeating myself.
The bottom line is that running at/near idle for a few minutes then shutting down for 90 minutes does not meet the requirements for having a 'warm' engine. Perform a minimum of a five minute warmup.
Setting takeoff power on an engine that isn't thermally stable is hard on the engine. The impact can be anything from a tip seal rub (permanent performance loss) to in extreme cases it can cause an engine surge.
Saving a couple of gallons of fuel by not doing a proper warmup will be quickly swamped by even a small increase in engine fuel burn until the next overhaul.