Hey Sam,
Get yourself one of those "Samadams", and sit down and read the thread by in the link I posted above. ( thanks BroncoJoe) .
And you can use a test light in lieu of a voltmeter.
You need to start with a check of codes as that is the starting point of diagnosing any problem that is engine management related.
There are many experienced minds on this forum, but in order to guide you on a correct path there has to be an accounting of known and correct information.
Your problem could be caused by a great number of things, and we have no idea on these older vehicles if the previous owner hadn't cobbled up something in the wiring!
The idea that someone could just tell you, "oh change the canutey valve, that will fix it" isn't realistic.
Diagnosis of a problem is methodical, and often time consuming. But!!! it is the path of least resistence when finding a cause of a problem.
So, relax, get your beverage, open that thread, and let's start to get to the root of your problem.