Dear Ford friends, I need your swarm knowledge about my old 87 XR3i convertible with 90hp KAT. I bought the car as an annual car and so far 171.000km on the speedo. Unfortunately, I don’t drive much with it anymore, also because it is in my mother’s garage for reasons of space. Yesterday the first time out of the garage took this year to drive to the Tüv. Tüv passed almost without any problems, only the Lambda value we have to manipulate a bit down over a maintenance of the exhaust the rear. Otherwise perfect condition, completely stainless and also the brakes impeccable. Over all the years very few defects had, sometimes a hydro-punch, pressure storage fuel, thermostat. At the very beginning times quantity divider / thaw disc, but that is 34 years ago. Now I have a sawing idle when it is warm. About all 3-4sec the speed goes down and if you give gas at this moment, you notice that it runs only on 3 cylinders. The Tüv did nothing, was j a while, even cold it runs clean. When driving I don’t notice it. Do you have an idea where to start looking or swap? False air, Lambda probe? Thank you in advance. Greeting TKS2007