Why does my RPM needle jump all over the place when I'm giving it the gas. But when I let off it goes back normal?

 

sounds like tyranny slippage.
does it pull or just rev when you punch it?

 

Does the tach needle jump when in Park or Neutral and the engine rev'ed? If not, then I agree with GreenBlazer2002....tranny slipping.

 

Do engine revs go up and down with the tach or does the tach flop around at constant engine speed?

 

In neutral or park, the needle jumps from idle to redline when the gas is applied.


The engine revs do not...

 

Hopefully a dirty electrical connector at the instrument panel (IP) but could be that the electronic tack has failed.
The electrical contacts on back of the IP are not the best; suggest taking IP out and cleaning them. Then reconnect without installing the IP, wiring harness has a bit of slack in it. Then start engine and see if tack operation is normal or by wiggling connector around it gets better or worse.
Could still be the tack itself. You could take it apart and try re-flowing solder connections or just get another one from a salvage yard or ebay.

Have fun.

 

Sounds like plan...gonna give it a shot this weekend!


Is the IP pretty simple to get out?

 

You will have to remove the radio bezel. Be sure you have all the bolts out before you try and tug on it or chances are you will break it as the plastic is old and brittle. And a replacement is $100 on eBay. I'v never seen one that wasn't broken already in the junkyard.

 

I've got the same issue with mine and am going to reflow solder joints this weekend. If you have a scan tool that will read RPMs you could plug it in and see if its the signal to the tach or the something in the IP. On mine, the signal to the scan tool reads fine, but the tach reads low and jumps. And this will also tell you if its the transmission that is slipping too, but you'd notice the engine racing if it were that. I don't know why people jump to bad transmissions and torque converters when they hear that a tach is acting up.