I'll be driving along going 60-70 in OD and all the sudden the tach will start twitching a few RPMS up. It continues slowly until it's jumping a thousand RPMs up and down (3000-4000-3200-3800, ect in a back and forth fashion) very randomly.

I just replaced all the major electrical parts, coil, rotor, ICM, dizzy, plugs, wires, yadda yadda yadda. It had been burning the middle plug wire on the passenger side so I had replaced it but now it's doing it again and the plug wire is fine.

It's random, sometimes it will do it and then not for several days and then it's back. If you let it go it becomes so erratic that it will die. It does it 90% of the time at speeds above 60 but it has happened a couple of times going 30-40. I had been able to drop it into 3rd and after a short while shift back to OD and it would disappear but it's not like that anymore.

Stopping the motor and letting it sit for a few seconds seems to reset the issue but it will continue to reoccur on the same drive.

Is this a flaky injector or something? I've always had carburated cars so this is new for me.

Thanks in advance!!!

 

Well depending on which transmission you have, I would put my money on a torque converter going bad. If you have a manual transmission, I would suspect a bad clutch/clutch component.

 

When I pull over and put it in park it will continue to do the erratic RPM although not as severly. I should've said that about two months back it slips out of OD when I start from park to about 30-40. Once it's over 40 or around 1500rpm it'll shift into OD just fine with a slight hesitation. It's an automatic.

Would the torque converter do this chaotic RPM thing in park?

 

its not ur converter u would know if it was it would feel like the trans mission slipping as the tach went crazy.

check all ur plug wires carefully, a arching plug wire will cause the tach to bounce like that. if the ignition system all checks out more then likley u have a bad wire to the tach and or the tach is just going bad

 

^ does your butt agree with the tach on the RPM changes, or is it just visual???

 

I can feel the car jerking so it's not just the tach misreporting. It will do it in park after a severe episode on the highway. Once it's starting doing it I can shift to neutral as I pull over and it's still jumping around and often stalls. After a few seconds turned off its fine for a few miles pr even the rest of a drive. I'm really confused by it.

 

Butt agrees

 

then its nothing in the transmission, my bet is on bad plug wires or something fualty in the ignition system, and oir a bad connection somewere