Hi Guys.
I have a 94 3.8 Lumina APV that isn't running great at the moment.
A couple of weeks a go I put new front and rear exhaust manifold gaskets on and I've been having rough surging idle and what seems like a big flat spot in acceleration since. If I accelerate or rev through this problem it returns to normal and will run beautifully all day long.

The problem started after I changed the gaskets and got plug wires 3 and 5 the wrong way round. I changed them back straight away and it started fine, but I've had this problem ever since.

I've checked vacuum lines and all the wiring and I don't see anything wrong.

Any help would be wonderful

Thanks in advance.
Tony