Let's nail this one point at a time. First, a transaxle is a front wheel drive transmission. Unless you've done some
SERIOUS modifications like Tim the Toolman Taylor, you don't have a transaxle OR shift solenoids. Shift solenoids are devices used to shift gears in an electronic automatic transmission. You have an AOD (non-electric) if automatic, and a T-5 if manual. Pull your plugs & inspect them before going any further. Have your fuel pressure checked, too. This'll eliminate a lot of headaches & time wasted.
Okay, on to your codes. 41 means "No HEGO switch detected--always lean (right HEGO)." 91 means "No HEGO switching detected (left HEGO)." Basically your HEGO's (oxygen sensors) are either shot (been replaced in the last 30-40k miles?) or the heater circuits have a problem. My money is on the latter if your HEGO's are relatively new and not cruddy, and that fuel pressure and the plugs both checked out okay. There's a common ground running to both sensors, and if this connection goes bad it can turn codes like this. Reason being the EGO's need to be heated to kick out a signal (does it run like it's lean???). Only other thing I can think of would be them being contaminated. Have you used RTV anywhere on the engine or sprayed anything into the throttle bore? If you need more detailed info, email me.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch 