You may want to consult an attorney to discuss any viable defenses under Iowa law. While I do NOT practice in Iowa, I recently had a similar case dismissed by the prosecutor in a WI case. My client was asleep in the driver's seat and the car was running. However, another person had started the vehicle before he entered, and WI requires that a defendant either drive the vehicle or operate some control necessary to set in motion. He did neither. On the other hand, the same facts would have definitely amounted to operation under the laws of other states, including MN. Therefore, it may depend on the explanation you gave the officer and/or other significant facts not described here.
Not legal advice. No attorney-client relationship exists between us.
In many states, you can be charged with OWI simply for manipulating the controls necessary to put a vehicle in motion. For example, if the truck was running and you were the only person in it, the inference is you turned the key in the ignition. The ignition would be a control necessary to operate a motor vehicle.
Just because you are charged, however, does not mean you will be convicted. To convict you, the state must prove you were OWI beyond a reasonable doubt. If the officers did not see you operate the truck, you may have an argument you were not operating. Also, you could argue you drank after operating the truck and parking. In some states, there is something called the shelter doctrine. If you had to keep you truck running because it was cold outside, you may have a defense to OWI under the shelter doctrine.
Bottom line: You should consult with a local, experienced DUI attorney. You may find such an attorney through the National College for DUI Defense: www.ncdd.com. Most initial consultations are free. So, you have nothing to lose!
I agree with the other answers that, yes, you can be charged with drvinig while intoxicated, which in your state is Operating while Intoxicated. Just the fact that you were in the vehicle and were in the drivers seat (or even elsewhere sometimes) and had the keys in the ignition (and sometimes not even in the ignition) can constitute Operation.
On the other hand, that may not fly with a jury at trial.
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