Most likely it is the vehicle speed sensor which is located on your tranny!
1997 cobra's have 305 horsepower. have a book on every mustang and cobra's ever built and specs.
locationof backup switch 1997 mustang
The 1997 mustang cobra came stock with a 32 valve 4.6 DOHC engine producing 305hp and 300lb ft of torque.
You can find a 1997 Ford Mustang Cobra fuse diagram in the car's owner's manual. You can also find it at various auto stores in your area.
possibly a bad/broken speed sensor located on the transmission
1964 1/2 Shleby mustang 1965 Mustang GT 1966 Mustang GT 1967 Mustang GT 1968 Mustang GT/CS 1969 Mustang Mach 1 1970 Mustang Mach 1 1971 Boss Mustang 1972 Mustang Mach 1 1973 Mustang Mach 1 1979 Mustang 1982 Mustang GT 1983 Mustang GT 1984 Mustang GT 1985 Mustang GT 1986 Mustang GT 1987 Mustang GT 1988 Mustang GT 1989 Mustang LX 1990 Mustang GT 1991 Mustang GT 1992 Mustang GT convertible 1993 Mustang GT/Saleen(possible) 1993 Mustang Cobra 1994 Mustang Cobra/GT 1995 Mustang GT 1996 Mustang Cobra 1997 Mustang Cobra 1999 Mustang Cobra 2001 Mustang GT/Cobra 2002 Saleen Mustang S-281-E/Mustang GT 2003 Mustang Cobra 2004 Mustang GT 2005 Mustang GT 2006 Mustang GT 2007 Mustang GT 2008 Mustang GT P.S. Shelby used to be the original mustang owner in the 1960s but in later years was bought out by Ford -Doug
You could have ignition problems if it is the engine causing the jerk.
The official top speed is 152 miles per hour but modified versions can exceed that.
Replace the instrument cluster.
You drive slow and change gears too soon.
this question should be listed under automobiles repair
I was looking for something similar, and may have inadvertently found the answer to your question. I found it at: http://www.allfordmustangs.com/forums/4-6l-talk/108372-1997-svt-cobra-engine-number.html Here's what "RandyStinchcomb" said: "well block casting #'s are above the oil pan rail behind the starter" Good luck. Signed, TAT 1997 Cobra