Steam from intake manifold region, 96 Mercury Villager


I have a 96 Mercury Villager van with about 135 K miles. I was aiming to sell it, but a couple of months ago it started shaking while driving. I ran the codes on it with an OBD-II sensor and it turned out to be the "knock" sensor, which lies deep down, underneath the upper and lower intake manifolds and underneath the coolant crossover tubes. Not being abot to sell it like that and being adventurous (plus it was expensive to bring in) I decided to try to tackle it myself, at the same time replacing various hoses, spark plugs, and air and fuel filters. It was a big task with lots of hoses, gaskets, etc. that I had to take out and then put back. I got to the sensor, replaced it, and then put it all back together. That took me 2 weeks, probably. Anyway, upon restarting (and it did restart!) I noticed steam coming from deep inside the engine and that steam smelled like coolant... Consulted some knowledgeable friends, etc. and decided I needed to go back in and use RTV on the gaskets I had just replaced. So, I went back in....
Now, a few weeks later, car is back together again and DOING THE SAME THING! Still lots of steam. I bought a radiator pressure tester, but that isn't showing any leaks. I really don't know what it could be unless I messed up on replacing the gaskets (and that would be the 2nd time - thought I was extra careful, too!) Any suggestions or do I have to bring the car into a shop (with my tail between my legs)?

PS I am relatively new to car repair, but have dived in with this one! Still want to sell it.

Thank you!

There’s no telling what you might have done wrong. Did you use new gaskets the second time (despite adding RTV)? Did you use a torque wrench? Did you chase the threaded holes with a tap and clean the bolts? Did you clean the mating surfaces thoroughly? Did you have the manifold checked for cracks or warping? Could it be something else like a bad head gasket, cracked head or even leaking water pump?