Help! Cruise Control Losing Speed (Sometimes)

[Coyote]

I have a '96 LT4 and have been having cruise control issues. When on the interstate the car will not maintain speed on a good level grade. I can set it for say, 75 mph. It will hold for a little while and then slowly start slowing down. It is still engaged because when I tap the clutch or brake you can feel it release. I checked the vacuum lines and the throttle for binding and found everything as it should be. Could it be one of the solenoid valves leaking by and not allowing enough vacuum to pull the throttle cable? It doesn't do this all the time, that's what makes it so frustrating. I am really close to disassembling the vacuum module and looking for trouble there. Anybody had this problem?

 

[LT4man]

Sounds like you could have a vacuum distribution problem.

Have you checked the three-port vacuum valve beneath the right hand side (passenger) fuel rail cover? This valve in located in the center of the intake manifold. Prone to cracking & breaking because of age and/or heat.

Check the vacuum reservoir ball on the driver's side next to the electric air pump. These are located right behind the front bumper cover.

The vacuum line from the check valve goes behind the intake manifold and ends up at the vacuum reservoir ball. The line is hard plastic but could be broken.

 

[jmhorn52]

Same problem

My 96 LT4 does the same thing. I will set the cruise and it too will start slowing down after a mile or maybe 5. ITs not much of a problem because I dont like to use the cruise all that much

 

[ajs]

I had a similar situation with my 88 and it turned out to be the hose fitting going into the PB booster was cracked. Replaced it and eveything is fine now.