Sounds like you got hit by one of the exploits that compromise your browsing .. I highly recommend Malwarebytes to remove the ad installer and any other malware. The download is a free trial of the full version of MB.. When the trial expires you have the choice of paying for the full version or drop down to the free version. The free version does everything the full one does except it does not offer full time real time protection.. You must manually run it if you suspect some nasty has snuck in. I have used the free version for years. It automatically checks for updates when you manually run it. you can download it here: https://www.malwarebytes.com/mwb-download/

I dunno but it sounds like compression numbers you're getting are pretty low. Around a hundred a motor will still run but getting it started might be tough - that is the issue, right? Anything that old that's been tortured likely needs rings & possibly valve work to run right. I'd say it's time to pull the top end apart and see what's needed.