Rough idle 1998 1500 goldwing tach jumping up and down

Check the connections on the fusible links. There are youtube videos on the subject

Its a 4.3 my first though would be if your not getting codes it throttle pisition sensor although it could be idle air control or EGR valve passages are clogged with carbon. Ihave the same thing except its in a blazer. Your going to have to pull some things off and look for things that don't look clean iac and egr although tps would be the first thing i would test you can do this a volt meter set to ohms take it off hook the meter to it and turn the inside of it if the meter dosn't go up evenly like the volume on a raido and starts ot jump around in a certin spot its no good

a coolant tempurature sensor will make it run to rich if it is bad. run rough at idle, and produce black smoke, engine may stall out. it also causes retarded timing, slow idle speed, cold hesitation or stumble, poor fuel milage. good-luck!! if light is on check for problem code. this will guide you in the right direction. if no scanner, any auto parts store will scan for free. repost if need be. have a good day!!

crank sensor is tied in with the tach. you have problem with crank sensor or electrical problem. the tach reads rpms, if the sensor is bad it throws the rpms way off. this is why you get the jumping in gauge.

does the tach jump from 500-1000 rpms ? check engine light on? if so check the 02 sensor, ignition modular, or crank sensor

COULD BE GROUND PROBLEMS OR THE TACH GOING BAD.EVEN THOUGH CAR SEEMS TO BE RUNNING GOOD IDLING GOOD.SOME TIMES A SPARK PLUG MISFIRE.CAUSING A LITTLE ROUGH IDLING CAUSING TACH NEEDLE TO GO CRAZY.I SEEN ALTERNATOR WITH VOLTAGE REGULATOR GOING BAD CAUSE A POWER SURGE CAUSING HEAD LIGHTS TO DIM A LITTLE THEN BRIGHT WHILE ENGINE IDLING.THIS WILL CAUSE TACH METER NEEDLE BOUNCE AROUND ALSO.

sound like its missing
check sparkplugs wires and coil pack for fire if not that run a compression check

have you checked the EGR (exhaist gas recirculation) valve? sometimes carbon will chip off and make them stick partially open causing extremely rough idle or wont idle at all without help from throttle

hi,seem you have leak on intake manifold or rubber seal on injector nozzle,be careful drop a little amount on kerosene on intake manifold and nozzle,observe if your idling get high the is there,maybe renew rubber seal on intake gasket,ty