'91 Volvo Auto-transmission

My transmission does not shift into overdrive for the first 20 miles or so on the road – longer if cold, shorter sometimes if warm. My mechanic tried changing a relay switch in the dashboard, to no avail. He thinks it’s a celenoid in the transmission and is waiting for a used one to come in for the part. He advises me in the meantime to get an extra key, leave the engine running and lock the door when I have to stop awhile, but I live where I must take a ferry to the city, and ferry personnel do not take kindly to engines left running! Help?

I suspect the dreaded ‘morning sickness’, which is common on older, worn down transmissions. I’d just live with it, because the only real solution is to re-build the transmission. You can try to replace the solenoid, and you may get lucky. But I fear it will not.