Hard to crank

Just started having a strange problem with my ‘90 teg. When I crank it cold or hot, it will turn over fine but when I release the key, it goes dead like I turned the key off. I have just installed a Bosch 02 sensor, but that didnt seem to help. I have discovered that if I turn the key to the "on’ position and wait for about 5-6 secs, it seems to crank fine and the car runs fine after that. Any ideas??? Thanks.

doesnt the car whine if you dont release the key? hm tough one. check the haynes manual troubleshooter