hi, I have a 12 HT in a 86 HJ61 (auto) that runs fine on the road and when cold but after driving for about 30 mins. With the car in Nuetral or Park the engine rough idles/misses in the rev range 1300rpm to 1500rpm and then runs normal/smooth above or below this range. I have tried injector cleaner, and doing a search online here without luck. the engine has 261K on it and looks to be un touched. any thoughts ?????