cruise control hunting (but speed almost constant)

[cypher007]

ive asked on the VOC UK forum, but hit a dead end.

my car's cruise control, until laid up, worked ok. now it holds the speed as far as I can tell, but if I watch my turbo gauge or mpg it varies by about 5 mpg up and down over about a 30 second interval. I can even feel it pulling ever so slightly.

tested from the vac pump end with the mityvac. pedal to the floor and it held it no loss of vacuum.

tested the vac pump output got 20inHG. turned pump off held vac until regulator disconnected.

tested vac pump pulled pedal to the floor and held it even with pump off.

so no vac leaks.

tested resistance of pump motor and got about 6 ohms, apparently it should be 17 ohms. so maybe the motor is not behaving as the ecu expects.

regulator checks at 101 ohms.

checked onboard diag and no errors.

what I do wonder is how the system varies the pedal position? is it using the regulator to bleed some vac off?

[MadeInJapan]

If the speed is holding, I would think that things are working correctly...increasing or decreasing rpm's is a normal thing to keep the speed constant. That's my $0.02 but if the pump motor is off (low ohms), then it might be worth sourcing one from a junk yard and trying it out to see if it makes a difference. My cruise control on my S70 has been broken for years...It was the stalk at first and I'm pretty sure it's one of the vacuum lines this time but I've been to lazy to fix it with other more important things with other cars. I always realize it's broken and I should fix it during one of the rare moments that I wish I had it, which is almost never these days.

[cypher007]

this didn't do it in the past. I can set a speed and it will hold, as best as I can tell due to a certain amount of damping in the speedo's reaction time, but watching the mpg readout tell's the system is opening and closing the throttle between 2 points.