cruise control surging 91'

[Tony H]

I had a long road trip this weekend. All was good with the cruise. Pulled in to get gass on the interstate, get back up to speed hit the SET on the cruise and I get this Surging. Felt like I was in a row-boat. I left it for a full minute figuring maybe it was hunting for the correct speed. no change.
On the way home many hours later I tried the Cruise again...same thing.

Any ideas? Seems odd that it was perfect until I turned off the car for 5 minutes to gas up. That's what's making me think that it isn't a Vacuum line.

 

[410Fortune]

Sounds like a vacuum leak for sure.
Check the cable linkage from cruise canister to throttle bodyfirst.
Then check your vacuum lines, also the early 4.0l"s are known for vacuum leaks around the lower intake.

Your cruise control depends on the speed sensor (end of the speedo cable) for the signal, does your speedo work okay?
It uses vacuum to control the throttle.

 

[Tony H]

Speedo works OK.. Well, the cable is fine but on Cold mornings, The speedo will Pin itself when I'm only doing 55MPH. That last a while . My guess is the the Speedo itself has grease on it and it has to warm up.

I'll hunt down for vacuum leaks. That makes sense it was just how suddenly it pooped out that made think it was something else.
Thanks

 

[410Fortune]

hmmmmm I would remove the speed sensor from the T case housing (1 10mm bolt) and take a look at the plastic gear.
You might consider a new speedo cable, Autozone has them for like $20.