RPM flutter killing cruise control

[Guest smith356]

I have a problem where my cruise control just drops off while going down the road. It still registers cruise on when it does this, not resume. At first I thought it to be a vaccuum problem, but noticed my tach would go up and down 3 to 500 rpm occasionally and I think this is causing the cruise to drop. It idles and runs fine, but I've noticed at highway speed that it will flutter like this and occasionally I can actually feel the miss.Does this sound like the often mentioned coil pack ? I'm sure I need to look at plug wires and plugs, too. Anyone else have this happen to you ?? Thanks, Jim.

[Guest crtnrds]

I've noticed that in 2 of my '89s that when coasting @ 45-55 mph the rpm drops & surges slightly fairly continually.

[2seater]

Possible problem with one of the switches on the brake pedal arm. If the switch is out of adjustment it can cause the cruise control to drop out or, the torque converter can unlock, changing the engine speed by a few hundred rpm. Also common for an ignition miss to show up around a 50 mph speed as well. The engine is under fairly high load at low rpm, where it is just shifting into fourth gear and locking up the converter. As the speed goes higher, the symptoms should lessen.

[Shelby]

It might be a vacuum leak.

There is a small black vacuum tube that run from around the teves master cylinder to the hvac controller inside the cabin.

It can get brittle and split. It can give you fits.

[Guest F14CRAZY]

I agree with Shelby. If you haven't replaced any vacuum lines, I seriously suggest doing so. Replace like all of them you can reach under the hood. If they're cracked, or you run a finger on them and it turns your finger black, they're bad. The vacuum could very well be leaking.

[Guest jcc3inc]

On my recently aacquired '91, the speed would first slow down when I engaged the cruise, then it would take over and work OK. It turned out that the vacuum hose to the brake pedal was "tired" and leaked; it took a short time for the vacuum to build up and thus the delay. Putting a ty-rap around the leaky end seemed to cure the problem.

As you probably realize, stepping on the brake pedal dumps the vacuum on the cruise control.

Regards,

Jack C.

[Guest smith356]

Thanks, everyone, for the input. I'll be checking vaccuum lines and plugs & wires. Much obliged !!