Strange Question

[blockphi]

I have a strange thing happening with my car. It is not a big deal, per se, but I think it might be an indicator of something more serious. When I try to use the cruise control on the Interstate and set it at, say 85 mph, within a few minutes it creeps down to 75 mph and stays there. I have tried setting it at 80, 90, and 95, as well as setting it closer to 75 to see if it is some type of computer glitch causing the cruise to read the mph as 10 mph less than it should, but in all cases it coasts down to 75 and stays there. Any ideas as to what could cause this? Help, I need my cruise! (I recently got a ticket because I like to drive way too fast without it!)

Thanks all, NB.O rocks!

[boblamb58]

It's a warning.. slow down

[blockphi]

I don't think that will be happening! I like driving a touch too fast for my own good. Since I drive about 100 miles a day, the cruise would be nice to have in working order.

[DR.billZ]

Uh..........let me get this straight. You are using the cruise to "keep from getting tickets". The cruise seems to 'set itself' at 75. Sounds like it knows how to avoid a ticket better than it's owner...............
Unless you live where you can drive over 75(and that isn't many places in the U.S.) then I'd kinda be happy.

[blockphi]

While I appreciate the fact that everyone is so concerned about my speeding habit, it seems that the point is being missed. If the cruise is not working properly, would it not seem that there is something wrong with some aspect of the vehicle? I am genuinely trying to get some insight into what could be causing this so that I can fix the issue, hopefully bypassing the stealership in the process. I am not looking for advice about my driving habits. Thanks.

[hannaco]

The cruse control is part of a closed loop control system consisting of the ECU and the injection pump. The ECU monitors the motor speed via the speed sensor. If the engine RPM changes, the ECU will direct the injection pump to increase or decrease the amount of fuel injected into the cylinders. A secondary control function is to control the angle on the turbo inlet vanes that controls the amount of boost needed.
Most likely points of failure are the speed sensor, the N-75 valve that controls the turbo, and the injection pump.
A good diesel pump shop that has the VE certification can check out the pump. They might also be able to check out the other items as well. Otherwise drive very quickly to a good repair shop.

[blockphi]

Thank you for the response. Last night, out of curiosity, I unplugged the mass air flow sensor to see if that would make a difference as the car was also acting a touch sluggish on hills and such. This morning, I set the cruise at 85 just to test and it worked just as it should. I am going to purchase a new MAF and install that and hopefully the issue is resolved. If it starts doing the same thing, I will take your advice and find a reputable shop to take it to. Thanks again.

[jpdeuce]

If the cruise stops working altogether it's probably your brake light switch. I haven't heard of the cruise adjusting itself before though. Let us know what the result is of your "fixing".