I have an 87 Mustang GT that’s driving me crazy. When driving the tach will go to zero but the engine keeps running but goes to idle. It doesn’t matter where the gas pedal is ,then the tach comes back and it runs fine for a short time and then it all happens again. This car has a list of new parts starting with computer, complete new distributor, wires and plugs, map sensor, coil, clutch switch, ignition switch, coolant sensor. The car is all original except for cat back. It does not have the Maf sensor. We’ve also cleaned all the grounds and replaced the battery cables. There are not any codes. It also has a new pigtail on the TFI. It does seem like if you push the clutch in it will start working again. Any suggestions will be appreciated