Any idea what would cause my tach to drop to 200rpm when I pull up to a light? I noticed it for the first time on my way home tonight. I don't think the engine is dying down that far because it idles pretty smooth, and when I got home I popped the hood and it didn't seem to be running any slower than normal. I have no way to check the actual rpm's but I would think 200rpm would be visually noticable. I was curious if anyone knew where these tachs pick up thier signal from, cam sensor or crank. I would think if it was something like that the truck would run like $hit or not at all. Anyone else had a problem like this?

 

The past couple days mine has been doing this also. Granted, its the 4-7, so could be something totally different from yours. Mine usually idles at 700rpms, now, every once in a while, it'll drop to 500rpms. Just makes me curious, I don't think its a major concern, hope not anyways...

 

Maybe clean the throttle body or a dirty air filter?

 

If it's just the tach and it's running fine I'm not gonna worry too much about it. I'm just worried it's a tell tale sign of something else. I just got the truck a week ago and really don't know the history of it. And I don't want to drive 2.5hrs back to where I bought it if there's nothing really wrong with it. Kinda hopeing it would be an easy fix before I had to jump into a warrenty issue.

 

Yeah, I'm gonna try that tomorrow along with 16 new plugs. It about to turn 50k and like I said, I don't know the history. That's why I don't like buying used. You never know how the previous owner took care of it.

 

Could be the plugs. They're certainly due. My vote is TB or air filter. A Seafoam treatment won't do any harm, either.

 

mine started acting up at 35k miles..i dont know the exact part name but the idle control sensor was dirty in the throttle body.

 

Well, it's definately something in the dash/cluster. I drove about 30mi round trip to Advance & the base and it worked fine till I almost got home. I stopped at a light about 2mi from the house and the tach dropped to 200rpm. I tapped the glass a couple of times and it seemed to jump a little bit. So, I gave the top of the dash a good rap with my hand and the tach popped back up to 500-550. After parking back in the driveway it dropped to 200 again. Guess I'll have to tear the dash apart and see if I can find any loose connections.