Unter anderem...
The differences between MD-82 and MD-88 are:
MD-88 has improved cockpit with EFIS, a choice with reference systems, with an inertial reference system as standard fitting and optional attitude-heading equipment, optional second flight management system computer, light emitting diode dot matrix electronic engine and system displays, a Honeywell windshear computer and provision for an optional traffic-alert and collision avoidance system were also be included
MD-88 interiors were improved with 12% increase in overhead baggage space and stowage compartment lights that come on when the door opens, as well as new video system featuring drop-down liquid crystal display monitors above
MD-88 uses more composite materials in its airframe
MD-88 uses the JT8D-219 or -217C (incorporates -219 performance improvements) engines, which are rated at 21,000lb (93.4kN) and MD-82 uses the JT8D-217 engines, which are rated at 20,000lb (88.8kN), but many airlines have converted the engines of their MD-82s to -217A/C or even -219
MD-88 has a heavier MTOW of 160,000lb (72,576kg), which is the same as in MD-83, in MD-82 the MTOW is 149,500lb (67,813kg)