I trying to track down a problem with my 240 that I think is related to a vaccuum leak. The car runs very rough at idle and cannot be driven at low rpms. If the idle is raised to around 2500 rpms the roughness goes away and the car can be driven on the highway if the rpms can be kept up. Intially I thought that I had a bad AMM or an IAC, but I tested both of these and they appear within the acceptable ranges. I have been searching for a vaccuum leak, but have been unable to find one. I have tried to locate it using a propane torch and also spraying carb cleaner around the fuel injectors and intake manifold. I attached a vaccuum gauge to the hose that runs from the FPR to the intake and vaccuum gauge read about 15 and rose steadily with the idle. Is this an acceptable reading?

One thing that seems strange is that the idle surges if you hold it steady around 2000 rpms. If you put the car in neutral and sit with your foot on the gas around 2000 rpms the idle will surge up a hundred rpms or so every 10 seconds. Maybe this is electrically related? I did clean all of the ground points and tested the resistance on the coil which was a little higher than the reference points in my Haynes manual. Could a bad coil produce the symptoms that I have? Thanks for all of your help as always.

Greg