Essentially the Fifth Ave stayed pretty much the same with some slight differences.....
1984 - New Yorker badge replaced by Fifth Avenue badge on trunklid; "Fifth Avenue Edition" badge continues on the rear doors, a new steering wheel was added. The regular Pentastar was replaced by a crystal one and was now used on the hood ornament and steering wheel this would continue through the end. Wiper arms were now black (instead of silver). Engine blocks were also now painted black (previous ones were painted light blue) Optional 10 spoke alloy "Road Wheels" were replaced with new optional "Snowflake" alloy wheels.
1985 - New black gearshift knob introduced (1982 to 1984 models have chromed knobs). Turn signal lever is now also black (1984 and below models were interior color keyed) with the exception of models with two-tone paint. The*carburetor*was switched from a Carter 2bbl to a Holley 2bbl as a result horsepower increased from 130 to 140 and torque was also increased to 265 (from 230)
1986 - New-style ignition key and center high-mounted stop lamp (the latter a federal mandate) introduced. Models with two-two paint had lower roof lines.
1987 - New steering wheel; final year for optional alloy wheels, two-tone paint, and rear stereo amplifier were offered. Also the last year for 17-ounce deep-pile carpeting and the last year the radio, headlight switch and climate control panels were silver.
1988 - Vinyl roof restyled; lower edge of sail panel covering extended below chrome window sill moldings. "Fifth Avenue Edition" badge replaced by a crystal Pentastar surrounded by a gold wreath. Driver's side seat now had a manual recliner (previous models had 6-way power adjusters, but no recliner). Front headrests were more cushioned. Some radios were replaced with new ones. Door panels are restyled and new power mirrors are standard. Passenger side dash vents were now interior color-keyed (instead of black with chrome trim). A new overhead console with map lamps, compass/temperature display and sunglass storage became available. A driver's side airbag and padded knee bolster affixed below the instrument panel became optional in May.
1989 - Driver's side*airbag*is standard. At the time the Fifth Avenue (as well as its M body twins) was one of the only cars that offered an airbag with a tilt steering wheel.
There's also lots of info on the mighty Fifth here.
http://www.allpar.com/model/dodge-diplomat.html
