I recently gave my car to my wife and bought a truck and I rarely used the cruise control. It had probably been 6 months or more since I used it last and it has worked fine since new. She tried to use it the other day on the highway and it just jerks the car, as if I were pressing and releasing the gas constantly. It is soo bad you cannot use it or it will make you sick to your stomach.

Any ideas on what might be causing it to happen. Other than that the car runs fine. It is a 2004 Sport 2.3 5 spd with 93,000kms.

Thanks for any info, John.

 

All I can say about that John, is that the cruise control is completely controlled by the PCM (Programmed Control Module) which in turn operates the ETB (Electronic Throttle Body.) I'm not quite sure where it, what sensor it reads the cars speed from, but since the speedo is also controlled by the PCM and you are not complaining that it is going crazy, I will assume that is not it.
It sounds to me that somehow the PCM has lost or has corrupt software programming and it may need to be reprogrammed in order to straighten it out. That's my best guess.

My quickest/easiest/cheapest suggestion is to reset the PCM.
Disconnect the neg battery cable for 10-30 mins. Reconnect and drive. If you're really worried about it resetting properly, turn on the headlight switch and leave it on during that time to drain any charged capacitors in the system. This will NOT drain the battery.
That may just solve your problem.

 

Hey virgin1, I did disconnect the battery, twice and it didn't help. That's about all I've tried and I can't really think of anything else to do. The speedo works fine and so does evrything else.

I might disconnect the battery and leave the lights on to see if that may help but I don't feel like that will fix it.

Thanks for the suggestions tho.

 

Chances are if you've tried that already that doing it again won't help then. Sorry 'bout that. That trick has been known to fix a multitude of other sins, so I thought I'd throw it out there.
Well then, we are back to re-flashing the PCM and that can cost a few bucks. I hope it turns out to be something simpler and cheaper for you though.
Sorry, but that's all I have to offer for suggestions.

 

When cruise acts up, does it hold speed lock for a while, then behave as if "cancel" had been selected for a little while, and then spontaneously kick in again, bringing the car back up to its previously preset speed, as if "resume" had been selected?
Or is it just going all to hell without rhyme or reason?
If after misbehaving, the car always goes back to the same set datum speed for a while, then it's likely that both the PCM and the ETB are behaving, and the cause is related to the cruise control mode/ set switch panel insert on the steering wheel, or else to a broken wire/ bad connection in the clockwork cable spring assembly used to couple the wires from the control panel on the steering wheel to the car's wiring harness.
Sometimes you can diagnose this by getting the car into cruise, and "twitching" the steering wheel to and fro to see it this aggravates the situation. The other thing you can do is squirt a dose of contact cleaner into the switches on the cruise control insert on the steering wheel.
When you want to do a PCM reset, all you need to do after unhooking the battery negative, is to open the car door for about 30 seconds; this is enough time for the current in the courtesy light circuit to discharge the capacitors in the PCM memory hold.
Finally, if you decide to mess around with the cruise control switch insert, you must disconnect the battery, and you must proceed with extreme caution- because of the air bag. (I wouldn't go there without using the shop manual).

 

Thanks oldeng. It happens as soon as I turn the cruise on and does it until I turn the cruise off. I tried driving for miles and miles one time just to see if it would stop and it did not. It feels as though I am stepping on the gas and releasing, stepping on the gas and releasing.

I am not going to put any money into trying to fix this particular problem. I've recently put both front bearings in and new pads all around, rotors on the rear and had some body work done. I now have an axle clicking so i need to prepare to replace that.

I don't really want to take anything apart near the airbag, that just sounds scary.

If I did want to, how would I go about flashing the PCM? the dealer only or any garage? Can I do it myself? rough estimate on cost?

Thanks again, John.

 

I was just checking through my Mazda Protege shop manual (2000) and I noticed that the cruise control subsystem has its own OBD which differentiates between actuator, processor, and input/output DTCs; a Mazda dealer having the proper scanner ought to be able to give you the lowdown on your grief.

 

John, I know that there have been several PCM software updates for the '04's. If yours hasn't had one yet or ever, perhaps it's time to look into it. That too may solve the problem and make the car more enjoyable to drive overall. (re: It may be worth the $$$ to find out.)