Toro has manuals both service and owners online for download. Based on serial number might be able to find some clues about that in the service manual.
www.toro.com
Since it happens when you touch the throttle wonder if there is a throttle position sensor that could be flaky? Also is it a diesel engine? Wonder if "recycle" refers to emissions control systems if it has the exhaust filter that cleans itself every so often? Just guessing, no experience with these and from a couple manuals I pulled up they look to have a pretty complex electronics on them.