Odd cruise control behavior

[Human]

I seldom drive my '95 CS convertible (3.1L) on the interstate but I did last night, coming home from a friend's since it was too cool out to put the top down as I had done earlier in the day. When I put the cruise control on, I noticed a very strange phenomenon. As soon as I pressed the button in the end of the turn signal stalk, the throttle opened up and sustained almost 3,500 RPMs. When I disengaged the cruise, I could maintain pretty much the same speed at a little over 2,000 RPMs. Either way, it sort of felt like it might not be going into fourth gear. The shift indicator is messed up so that it shows neutral when I'm in overdrive and overdrive when It's in third. I've gotten used to pulling the shifter back to the detente that should be overdrive, then nudging it forward a notch to actually put it in overdrive and just kind of feeling for reverse since the indicator doesn't show anything for reverse but shows reverse for neutral. The car has a rebuilt transmission with just a couple thousand miles on it. I'd hate to think it's already going bad.

[RPE1992GPSE]

How many times have you tried using cruise control since the transmission rebuild?  Was this the first time this occurred while using cruise control and since the rebuild?

Was your shift indicator always like that, or only since the rebuild?

Is your "SERVICE ENGINE SOON" light on?

[Human]

I've used the cruise control several times since the rebuild. Sometimes it works just fine and sometimes it doesn't work at all. Turning the engine off and starting it again seems to reset it. I drove the car today for the first time since I started this thread and it worked with no problems. The shift indicator has always been a little off. Before the rebuild, Drive would actually be Third but the issue with reverse and neutral started after the rebuild and seems to be getting a bit worse. At some point, I need to take it back to the transmission shop and see if they can fix it. The rebuild has a three-year, 30,000 mile warranty so hopefully they can do something. 

[RPE1992GPSE]

The park-neutral position switch (PNP) could be the culprit with both the shift indicator being "off," as you describe, and causing the erratic shifting behavior.  Now, I'm not 100% on a 1995 vehicle, but the cruise control could be vacuum operated like it is in the older W-bodies.  If you have a disconnected or damaged vacuum line under the hood, it could cause the cruise to fail to operate.

[Human]

I was driving the convertible on that same stretch of highway last night and when I engaged the cruise control, everything worked as it should and the engine was turning at around 2,000 rpm. I'm now reasonably certain that what happened a couple of months ago was the transmission was in third instead of overdrive and thus couldn't shift into fourth gear.

[94 olds vert]

9 hours ago, Human said:

I was driving the convertible on that same stretch of highway last night and when I engaged the cruise control, everything worked as it should and the engine was turning at around 2,000 rpm. I'm now reasonably certain that what happened a couple of months ago was the transmission was in third instead of overdrive and thus couldn't shift into fourth gear.

I have done that as well and was wondering why my cruise control wasn't working. No harm done, except burring some extra fuel. 

[Human]

So yesterday, I had a little epiphany about my sometimey cruise control. Could it possibly be related to my sloppy shifter? I've complained before about the shift indicator on my '95 Vert being wildly inaccurate to the point of having to literally hunt for the proper gear. When the transmission is in reverse, nothing is lit on the indicator. In neutral, the N may or may not be lit. In drive, the N is usually lit. I third, the D is usually lit. Often, I'll be going down the road and notice the car is in third (looks like it's in drive) and have to give the shifter a little bump forward to get it into drive.

Yesterday, the cruise control hadn't been working but then I noticed it was in the wrong gear and bumped it into drive. A little while later, I turned the cruise control switch off and back on, then tried the cruise again and low and behold, it worked. I'm not sure what to make of all that but it seems there could be a connection.

[94 olds vert]

38 minutes ago, Human said:

So yesterday, I had a little epiphany about my sometimey cruise control. Could it possibly be related to my sloppy shifter? I've complained before about the shift indicator on my '95 Vert being wildly inaccurate to the point of having to literally hunt for the proper gear. When the transmission is in reverse, nothing is lit on the indicator. In neutral, the N may or may not be lit. In drive, the N is usually lit. I third, the D is usually lit. Often, I'll be going down the road and notice the car is in third (looks like it's in drive) and have to give the shifter a little bump forward to get it into drive.

Yesterday, the cruise control hadn't been working but then I noticed it was in the wrong gear and bumped it into drive. A little while later, I turned the cruise control switch off and back on, then tried the cruise again and low and behold, it worked. I'm not sure what to make of all that but it seems there could be a connection.

Yes a sloppy shifter will not allow your cruise control to work. I have dealt with this issue before, never on a w-body, but with my 2006 Silverado. You can be in D, but if something isn't aligned correctly and the car thinks you are in N or 3rd your cruise control will not work. 

I had to adjust the linkage down by the transmission. Once I got that right my cruise control worked again. Also it is nice have the shift indicator in the correct spot as well. 

[Schurkey]

Not sure I've ever tried it, but I'd expect the cruise to work in Overdrive, or Drive.  (4th and 3rd)

 

Every time the cruise has been goofy on my 92/93 Luminas, it's due to a broken vacuum hose.  The tubing gets brittle, cracks, and then the cruise system doesn't have vacuum to run the actuator.  Both cars have multiple splices to the vacuum tubing.

Edited May 20, 2022 by Schurkey