That sounds like the "limp home mode". The ASR system is very complicated (read: I don't really know how it works). I've gone into limp home mode once, and that was for about 30 secs. I shut off the motor and restarted...never have had the problem again (~25K miles ago).
I guess if i had problems with ASR, the first few things I would do is the easy stuff:
1) disconnect the battery for a couple minutes and reconnect...I've heard of one person who did this and it worked; apparently it resets the system.
2) Another 'no-cost' thing I'd do is make sure that the entire linkage (ie, all the little ball/socket connectors, etc) are absolutely clean and lubed with ATF.
3) Then I would make sure that all the axle sensors and various relays and connectors are clean and not damaged.
There are then several tests that the manuals go thru to check the system, including adjustments. The ASR system has at least 15 electronic/electrical components, 5 hydraulic components and one mechanical component. It's tied into the ABS system and the Tempomat cruise control system.
I believe you would be wise to get the manuals and understand the system more before you dove into it. Or you may want to take it to someone who understands it and has worked on them before. There are expensive parts in there.