1989 5.0 Idle Drop And Bouncing Tach

Jamesrolls5point0

New Member
Oct 25, 2015
18
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Hey all, I wish I could have a happier first post but after several suggested prior fixes I've read im alittle lost here,
Car is a 1989 hatch, 5.0 near stock motor
(Cold air fender intake and msd dizzy, cap, coil, wires , new 190 fuel pump )
Trans is a 3550 tremec
Anyways this problem started on a road trip (farthest I've driven the car ) from NYC to Ohio , the last hour of the way the car starts bucking really hard every time I let off the gas to say , slow down or if I slowly easy off to say 1000~ rpm in 5th

It felt like Id catch a chipped tooth or something in the rear diff every few feet , I get to Ohio , pull my fluids from trans and diff , all normal and put new fluid etc
Car doesn't do it again for another 2 hours
In order to make it home I had to stay either in 4th at high Rpms of be running near 90 to keep enough revs in 5th
I drive it around for a while no problems in lower gears, now it started doing it at idle so I know it's not a clutch or drive drain problem, if I let the car idle for some time it will be happy at 750 ~ then drop to like 200 for a 1/10 of a second and shoot back up to where it rests
That's at idle

If I'm driving and let of the gas it does the same thing or if im at 2000 or up and say let off the gas quickly or something to decrease revs my tach bounces wildly around

Changed IAC and TPS same issue , reset computer same issue , fuel filter , different brand gas , all 93 octane , timing is perfect

Thanks in advance

I have a video of tach bouncing if you'd like to see it let me know , still trying to get a video of the idle drop
 
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