SteveNC

Recently I made a trip to the outer banks NC in my '83 RX-7 and on the way there the cruise control started acting up. At random the car would begin accelerating from the set speed and before I knew it I would be going 5, 10, 15 over the limit if I wasn't paying attention. Any advice on what could cause that type of behavior?

As far as I can tell the cruise is factory installed. Every time I noticed it happening I was at cruising speeds of 55 or 65 or 70 mph areas on level ground with the cruise set to prevent me from speeding. It was not like it was flooring it, just slowly gaining speed; usually I noticed it was happening when I was going about 10-15 over and I had to either tap the brake, clutch, or flip the switch off then back on and reset the system. There was no specific time between when it would act up and when it would be OK. Sometimes it was just a few minutes, other times it might be a half our before it acts up. Although I'm not positive, I believe it would have continued increasing speed if I had not reset the system.

t_g_farrell

iTrader: (1)

Maybe a vacuum leak? Aren't these things based on constant vacuum? Thats my guess.

DreamInRotary

iTrader: (49)

They are based on a vacuum line on the rear part of the rat's nest. Not sure if that would cause the cable to retract more, resulting in more speed or not though.

I'd check the mechanics of the system (test the lines it's connected to, electrical connector is good, etc.) and make sure everything is alright. Last resort would be buying another unit (I have one that I'm selling) that did work well when it was installed.

MazdaMike02

iTrader: (4)

A lot of times the vacuum nipple on the cruise control actuator itself cracks causing a vacuum leak. Or maybe its just the line itself that's cracked.

SteveNC

Thanks all, I'll troubleshoot this weekend and report back. I know the vacuum is what gives it the oomph to pull the cable and give it gas so I would assume that a vacuum leak would cause it to lose speed, not gain speed.

I've also read some info on the throttle position sensor causing issues and I know mine needs to be checked. Way back when I was having shutter valve issues mine was adjusted in a very unscientific way so I'm pretty sure it is out of adjustment...hopefully that is the cause as I'm sure all the repair parts have decayed into unobtanium.