Cruise Control Problem Continues

[grr]

1998, S70, T5, 300,000 mi.
For some time the cruise speed varies on this automobile, fluctuating up or down as much as 5 mph. All parts of the system seem to be functioning, but it won't hold speed, especially up hill, where it really over-speeds.

Then I got a code for the throttle position sensor, replaced it, but no change other than significant fuel mileage improvement.

I "looked" everywhere for vac line potential cracks/off, etc., but found nothing amiss. Pump under battery seems to be working.

Can one still test vacuum systems with ether for leaks, as in the old days?


Ideas anyone?

Thanks in advance.

Jerry

[rspi]

I'm having cruise problems as well. If the cruise works but will not properly hold speed, my guess would be a vac leak somewhere. You can jump the pump with the car NOT running but on. Pull the relay (control unit) next to the fuel pump relay. Then jump pins 1S to 7T and jump pins 3S & 7T to 9S (this jump wire has a double end and a single end). The pump will run and pull the gas pedal to the floor. Then you can turn the car off and the vac should hold for at least 30 seconds. If it doesn't hold, listen for vac leaks.

[matthew1]

^^^ Great way to find vac leaks, regardless! Thanks.