96 erratic speedometer

[copper_94]

my wife's 96 is having a speedo problem. it'll be steady for a while, then jump up 20-30 mph for a few seconds, then drop back down to what it should be. when it does this jump, the cruise control (if on) shuts off. very annoying on long trips.

the actual car speed isn't varying, but it's just the speedo changes. the tach doesn't change readings.

i'm thinking either a bad ground behind the dash, or is there a sensor somewhere on it's way out? it's been doing this very occasionally for a year or so, but it's starting to get worse.

thanks,
charlie
cave creek, az

 

[Nothwang]

Speedometer

Hi, been having similar problem with my speedometer only it fluctuates when in idle.Did you solve your problem?

 

[copper_94]

Hi, been having similar problem with my speedometer only it fluctuates when in idle.Did you solve your problem?

yes. remove the left side plastic cover. under it is a hard plastic tube that runs from a hole in the engine cover to the throttle body. on mine, the rubber adapter that attaches this plastic tube to the throttle body had a crack. it would open up when the engine got hot and leak air, causing the throttle body to vary the idle.

check the tube and both end adapters for cracks. i couldn't find another adapter as it has different IDs on each end, but a length of oil proof hose and 2 hose clamps worked.

i also replaced the iac before i found the crack, as that gave me the same symptom on my old 89. you might check that that is operating correctly and isn't carbon'ed up.