Don't know how to attach pics!
Not exactly sure on the 1800 but on my 145 the MAP is located on the passenger fender well. It has a big D-jet connector and vacuum hose attached. Google D-Jet MAP sensor for pics. In the middle of the back side is, from the factory, a glob of wax that covers a LARGE straight blade screw. It was put there to prevent tampering but that doesn't stop everyone.
Beneath that screw is a small screw that can be adjusted with the help of an exhaust sniffer and someone who knows what they're doing. I read that each D-Jet car leaving the factory got it's own individual fine tune at that screw and then it was sealed. Don't know if this will apply but it's a thought.