cruise control drops out

[combja]

My cruise control will set, drop out when braking and resume normally, then just drop out randomly.
Then, sometimes it will Resume on demand, sometimes not. Sometimes it can be re-set, sometimes not.
Turn it off/on then sometimes it sets, sometimes not.
Wait awhile, turn it on, set it and it will work for a while, then randomly drop out.
Any suggestions?

[GOLDCYLON]

My cruise control will set, drop out when braking and resume normally, then just drop out randomly.
Then, sometimes it will Resume on demand, sometimes not. Sometimes it can be re-set, sometimes not.
Turn it off/on then sometimes it sets, sometimes not.
Wait awhile, turn it on, set it and it will work for a while, then randomly drop out.
Any suggestions?

Do you have a FSM? There is a helpful diagnosis tree to follow.

[Young1]

Yes FSM. Check 30 year old vacuum hoses for cracks at bend going into module above battery. Probably minutely cracked. Trim off an inch or so and reinsert.

[combja]

What is a FSM?

[WARP TEN]

What is a FSM?

Factory Shop Manual or more correctly Factory Service Manual. They have diagnostic schemes for finding a vacuum leaks or other malfunctions. --Bob

[GOLDCYLON]

Yes FSM. Check 30 year old vacuum hoses for cracks at bend going into module above battery. Probably minutely cracked. Trim off an inch or so and reinsert.

Also check for cracks on the vacuum line supply in the middle of the passenger side of the plenum :cheers:

[Thomas ZR-1]

Check the vacuum switch down on the brake pedal...often cause leaks in the system.