I've been having an intermittent problem with the tach on my 4runner where the tach will read at or slightly above zero while idling. I managed to catch it on video, but it doesn't always do it. Any ideas about what could cause this? Bad gauge?

 

Yep loose and or dirty screws on the back of the cluster, should be a few threads about this issue.

 

CO, are you talking about the screws that hold the tach and circuits down to the actual gauge assembly? Both my '90 and my '98 do this, but only when cold. My brothers '94 does it when it's raining. I always though it was the temperature changing the resistance or something.

 

My tach seems to do it at random. Since it doesn't always do it, I'm leaning towards it being the gauge itself. If the connection screws were loose, it would do it all the time no?

 

Yeah the screws that connect the gauge to the flex circuit on the back of the gauge cluster are the ones I was thinking might be loose. If they're not tight it'll alter the resistence, increased corrosion, and intermitten contact and those sorts of things.

Loose connections will change conductivity, due to temp, vibrations, or even humidity. Also of course resistance changes some due to temperature shifts but shouldn't do this, auto electronics are well designed with a large temp range.

If they get loose enough it will stop working completely.

In the video it seemed to match up with the suspension/road noise, so I'm pretty sure something is going to be loose. But it could be something loose on the gauge circuit board also. If you get back there and find the screws are firm and tight you'll want to check the gauge per the FSM.

FSM link.

Here is a thread, that says it was his igniter ground, which is something you can try that doesn't involve taking apart the dash. Just clean and tighten the connections under the hood.

Here is a loose screw thread, he is talking about a fuel gauge but it's the same/similar situation.

And Another thread, this one contains a percussive test recommendation. Which I'll add doesn't always work in your favor, you might bang it loose enough it stops working all together.

 

What your sayin makes sense, cause a few "love taps" on the dash right above the cluster usually clears up the issue. What doesn't make sense for me is the temperature variance. On my trucks, it has only done it in low temperature situations, like below 35-40 degrees. I dunno though. My truck is gonna be off the road for a little work at the end of the month so I might pull the cluster while I'm at it.

 

i'm having the same issue on my 85. i'll try cleaning the ground connection, hope that solves it!

 

I'm going to try that too as soon as I get home. If it does happen to be the tach itself though, I have a spare

 

Well, I tried the "cleaning the grounds" solution, and it doesn't seem to have had any impact whatsoever. Banging on the dash didn't trigger the gauge weirdness, so I'm thinking that in my case it's the gauge itself. I'm not in any hurry to swap out the gauge though since I don't really drive my 4runner any more. I'll get to it eventually

 

I had a very similar problem. Sometimes it would jump all over, be wrong or die completely. It turned out to be a short in the IGN wire if I remember correctly, it comes from the igniter and goes to the cluster and diagnostic port. There is a elbow in the wire loom that goes to the diagnostic port and it had rubbed against the fender. It rubbed through the insulation grounding out the wire. I found it by having some one watch the tach and I wiggled all the wires in the engine bay. I was very glad to find it. I had already replaced my cluster and it was driving me coo coo. The connections in the back of the cluster are pretty crappy too, i would check them also.

Good luck