Thank you both. Today I inspected the wires and cap. Both are new within the last year as are the proper Bosch plugs. My neighbour removed the Idle valve and flushed it with Seafoam. All of the vacuum lines seem OK? The OVP is also new within the past two years and is the more expensive model. It will be interesting to see if this returns but for now I am driving my BMW 635CSi.