86.5 Speedometer and Idle Issues

[MadNad]

Recently, my 86.5 Supra speedometer stopped working intermittently. When the speedo stops working, the car struggles to Idle, bouncing around 350-650 and sometimes die. Sometimes after the car dies, the speedometer and idle issue go away after starting the car again. The issue seems to have gotten worse since I noticed it a couple of days ago. The car drives fine otherwise. Prior to this the speedometer gauge has been sticky for a few years.

I've done some research and it sounds as if the Speedometer sends a signal to the ECU and could cause idle issues. It also sounds like it is the short speed cable that usually fails. Weather hasn't been great so I haven't had a chance investigate further yet. I am taking it to my friends shop tomorrow (doing unrelated work replacing rear rotors, brakes & ebrake). I'll check codes later today.

My question for you all is that because the speedometer was failing intermittently, I was curious if this was more likely an electrical (bad solder joint?) issue with the gauge rather than a mechanical issue with a failed speedo cable. Thoughts?

 

[MadNad]

It actually sounds like a mechanical issue. My speedometer cable has been making squeaky noises for some time, I just couldn't figure out where it was coming from. After testing it again, I can hear the cable squeaks when the speedometer works, but goes silent when the speedometer stops registering.

 

[Jeff Lange]

The speedometer issue is pretty certainly a mechanical one. The idle issue is likely unrelated, but you say they occur at similar times. Not sure why that would be. The ECU receives no speed signal when you are idling (not moving), and typically the speed signal would not have much of a bearing on a Toyota ECU as old as the 7M.

Jeff

 

[MadNad]

Replaced the short speedometer cable today which fixed both the speedometer and idle issue.