I may be fixing your problem now
My 94 has been doing the same thing yours is doing for about a year. Idles rough, 11 MPG and loss of power but it runs decent on the road. I exhausted all possibilities and spent a lot of money before I finally did a compression check. WOW was I surprised! What I found was I had only 2 good cylinders. I could not believe the car even run. I naturally, as you did, thought it was HGs. So I pulled the heads off to find the HGs were OK. WOW surprised again! No breaks or cracks in the HGs or the heads and no broken head bolts. I even pulled and tugged on the HGs to see if I missed something. That made me scratch my head real hard but it made sense since I was not puking antifreeze or overheating. Been there, done that! However, that did not explain why the compression was low. So I took the heads to get them resurfaced and pressure checked. My machinist told me that I had 4 burnt exhaust valves and they were surprise surprise the 4 cylinders that had little or no compression. THe other 2 exhaust valves were on there way out. My point is do a compression test early to save yourself a lot of time and money. I wish I had!
Ed Springer
90 Black XR7 5-speed: 70mm TB, Fresh Air Intake, '94 Supercharger, 5% SC Pulley, Raised SC Top, I/C Fan, UD Pulleys, 190 l/h Fuel Pump, 36 lbs Injectors, Headers, Magnaflow Muffler (no cats) with stock resonators, 3:27 Gears, Ripper Shifter, 73mm CL MAF (Blue Tube), Magnacore Wires, NGK Iridium Plugs, Royal Purple Lubricants and Rear Spring Air Bags.
94 Red SC Auto: 70mm TB, Fresh Air Intake, Stock 90 SC Pulley, Raised SC Top, I/C Fan, 190 l/h Fuel Pump, Headers, Raven Muffler (no cats) with stock resonators, 3:73 Gears, Accel 36# injectors, 76mm C&L MAF (Gold Tube), Magnacore Wires, NGK Iridium Plugs, MSD DIS-4 Ignition Box with Tach Adapters, Royal Purple Lubricants, TRANSGO Shift Kit, Pro-Torque 2500 Stall TC, Haydon Auxiliary Transmission Cooler, Tokico Struts & Shocks, American Racing 17” Sniper Wheels, Michelin Pilot Sport A/S Tires and 235 RWHP with 315 LB-FT Torque.