Cruise control glitch - 1987

[Jeb]

I've got an 87 Convertible and about the only problem I'm having is that the cruise control doesn't seem to want to hold a speed.

I'll set it and it's fine for maybe 30 seconds and then the car loses speed at about 1 mph every 30 seconds or so. Tap the gas and it comes right back up to speed but then drops off again shortly thereafter.

I'm thinking vaccum leak but I've checked all the vaccum lines I can find and there doesn't appear to be a leak.

The ventilation system is working fine.

Any ideas?

 

[nyernga]

Could be a bad diaphram in the servo......could be


do you have an automatic or clutch?

Len

 

[Jeb]

Automatic.

 

[Cruise]

I am not sure if your '87 is similar to my '94, but when I had problems with my cruise and heater controls, they were both related to a plastic T valve that is located under the passenger side Corvette plastic head cover.
On my car, on the underside of this T valve, it had a hole that formed from melting.
Once I replaced this $10.00 T valve, my cruise has been working ever since.

 

[nyernga]

I ask because there's two pedal switches on a standard shift that will disable the cruise. Since you only have one, mounted above the brake pedal and if it's working ok, I would suspect the servo. I'll check ,y service manual for my 88 and see what I cal find out. It should be the same.

Have you checked for a vacum leak in the line coming off the brake pedal switch? It may have gotten "chaffed where it runs through the firewall. There is a procedure for adjusting the cable from the servo to the throttle lever also. It could be something as simple as that.

Len

 

[Jeb]

I'll check the vaccum line from the brake pedal switch. That's one I missed.

I don't think it's an adjustment deal simply because of the way it's acting but I'll look into that also. Sooner or later, I think I'll find a pinhole that allows the vaccum to leak off.