1991 lumina euro problem, dredded intake manifold gasket problem?

Hi, I have a question. My 1991 lumina eurosport recently started leaking oil. Turned out to be the front most valve cover gasket. To remove that I had to disconnect the bypass line that goes to, the throddlebody or intake manifold, I’ve been told both, but it connects to the top of the water pump and has I believe a heater core line to the side of where it connects to the water pump. Anyway, I took the screws out of the water pump and from the heater core lline and water pump, came antifreeze, from the metal bypass line, came pure oil. I had somewhere to be so changed the valve cover gasket and ran it line that with no obvious leak or anything since then, no oil and antifreeze mixing or anything.
really it has barely lost any oil since then at all if any and never lost any coolent in this whole thing. I can tell, the level is where it was in September when I got the car.

Last weekend, when warm, the car developed a miss. First it was off and on but going through our day it got worse. This morning, same thing it was fine, then did it a little bit, it’s like every time we shut it off and restart it it’s good for a couple minutes then comes back worse than before. If the engine cools down it’s great for a while until it gets up to temperature for a little bit. Exhaust smells and looks normal but not smooth rhythm to it. Also, today it got bad on the way home about 10 minutes from home so we got it home, and smelled gas strong. I cracked a plug wire, must be original as well so am replacing them and the spark plugs tomorrow. Checking spark plugs, the 2 I looked at seem sooty and old.

First question, with oil in that bypass line, am I correct in assuming I have the dreaded intake manifold gasket problem? If so, is that as bad to replace as it looks or should I be OK doing it in my driveway? Second, am I looking at 2 different problems? The miss and that oil? I’ve only really taken the car out a couple times since doing the valve cover gasket because obviously I have work to do. It has low miles on it and the price was right, seems like if I can fix it dsI’ll be in good shape for a while. It’s the 3.1 V6. I just want to see if I’m on the right track before I get on a parts changing spree, if the intake manifold gasket is bad it can’t be too bad, oil and coolent look fine from what I can tell but I have a replacement anyway. I also have new plugs and wires, if I’m going to have to get in to this thing, I was going to do them anyway since the rear ones are a pain to get to, if I have to take it apart anyway I’ll change them, I was told they were done a few miles ago but I’d bet the rear ones weren’t done.
It looks like someone’s been inside this engine before, I hope I’m not all wet and that oil isn’t remaining from a long past problem, I’m seeing no sign of oil and antifreeze mixing or in the other’s territory at all since then. That bypass line also now gets hot to the touch with the engine running and I don’t remember it doing that before.
Thanks for any help or suggestions.

An intake manifold gasket leak on the 3.1 almost always is a coolant leak. From what you say it doesn’t sound like that.

I’ve heard of it going either way, what confuses me is that now there is no sign of coolent and oil mixing at all anywhere, not that they did before noticeably. I don’t know, time to start pulling things apart. When it’s not missing it runs so good, plenty of power so nothing’s hurt too bad yet I don’t think. I’m hoping I can find/fix it before it is hurt.

OK, so things get stranger. We decided to go about our usual Sunday things today, it was cooler out than it has been and I don’t know if that has anything to do with this or not. Anyway, we took the car out to 3 places today, about 10-20 minutes each. It ran perfect, no miss, nothing. I don’t know if that gives anyone ideas but I’m having a bad feeling I’m going to possibly be chasing this one for a while if it’s going to be that off and on. Fluids and levels still look good too. Originally I had oil show up where it shouldn’t have been and more recently a miss, these aren’t things that just go away on their own

I have a feeling that the tube that had oil in it was your PCV tube. That’s normal. It runs from the inlet of the upper intake manifold (the air plenum) where the throttle body bolts on. The other end goes to the valve cover. If your oil and coolant levels aren’t changing and the oil doesn’t look like chocolate milk shake it’s very doubtful you have bad intake manifold gasket.

If the misfire comes back, and it probably will, you’re on the right track changing the plugs and wires but you may also have to change the three coils in your coil pack. I’ve seen this happen often on 2.8 and 3.1 engines, especially on the ones where the coils are mounted way down low behind the bottom of the radiator. I’m not sure when they moved them up top. If they’re the originals they’re 25 years old. They don’t usually last that long.

Was it a damp or rainy day when the misfire occurred. If so, bad plug wires shorting out to the nearest ground point.

I know where the PCV tube is, that isn’t where the oil was. The oil came from a metal line, it’s connected to the top of the water pump by 2 screws. Just above that connection to the water pump was a rubber lline which I think goes to the heater core though it’s hard to follow it, but that metal line comes up past where the rubber line connects then raps around behind the engine. I’m told it’s a thermosdat bypass and connects to the intake manifold. Honestly, give me an old carbureted engine I’d have it figured out, I’m a little behind on fuel injection but cathing up as years go by, then I see something different from what I’ve been figuring out.

The coil packs and module have been replaced on this, they’re not original but the coil packs are down low. I know one plug wire has a hole in it so I’m replacing them, I wasn’t doing it in the snow/rain today but I have them so will do that this week, I have wondered about the coil packs as well if it acts up after that.

It wasn’t wet the days it was missing, it was a little warmer than it was yesterday when ti wasn’t doing it. I can say I got the car in September with 91,000 miles on it, it’s got 5,000 more miles on it now so being the family car with an active family, we’re not easy on it and I’m sure some things are going to go bad because it basically hadn’t had 1000 miles put on it in the last 15 years until I got it. I already replaced a ton of brake lines.

Anyway, looking at all the bolts with antiseize on them and the markings, I’m thinking the intake manifold gasket was already replaced, hopefully with the updated one but I’m stil confused on oil in that metal line. I have half a mine to disconnect it again and see what comes out this time.