My Tach is bouncing around and I dont think that it is reading correctly anyway. This the sequence of events....My harmonic balancer broke and rather than trying to fix a bunch of other crap going wrong on the engine I bought a used engine from the salvage yard....put that in and then like a couple of months later the trans went too. NICE !!! Well my car doesnt seem to shift at the correct times. I was told that the trans computer may have a problem.....After all of that the tach started its craziness. I thought had to do with me changing my GXE gauges to SE gauges. Give me a clue what I need to do or check.

 

tach sensor is bad.

 

where/what is that^^^.... i might have the same problem, my tach is jumps between 1500-2000, and then will suddenly shoot back down to 750..

 

That sounds like a timing issue, or something else.

 

Well that wouldnt make sense that the sensor was bad because i got the problem just a little after the engine was changed....and then when i got the trans changed it really started to be a problem. Now it will completely tach out and stay there and eventually it will respond. So the speed sensor on the trans is what you think.....and not something with the distrbitor ? I hope its something really simple because this car is starting to nickle and dime me to death....and I really dont want to get rid of it for that reason...so help a brotha out !!

 

OMG I'm sorry. Not the trans sensor. I donno what the hell i was thinking. I was stuck thinking it was the speedo.

Ok, is the tach bouncing with the engine running smooth.

If it is, there's a bad connection either on the gauge, or possibly the sensor, I donnno where the tach sensor would be. Never fooled with it.

Or is the idle shifting with tach?

In that case it can be a number of things.
Really badly gapped spark plugs.
possibly cap and rotor.
spark plug wires.
Timing could of jumped(I had this happen, ran fine most times, ran like crap other times. bogging, high idle, surging.

I'm assuming you know how to check all those things, I saw how much work you did on your car. Good work.

 

YES !! You are dead on !! The tach bounces around but idle doesnt change, the car runs well and other times it runs ok, and sometimes the idle is high 1000-1300...but it eventually corrects its self. I am at an end so I may have to just take it to the dealer....at least then if I have a problem afterward I can make them fix it. Theorecticly !!

 

I have the same problem, it is so frustrating the car runs fine but the tach goes crazy. Let me know if you figure it out so i can fix it also. thanks

 

i had the same problem tried cleaning contacts ect ended up changing the tack it works fine now.

 

Same problem here. Engine runs perfect, but tack will bounce around sometimes. So has anyone had any luck with isolating what sensor is not working or if it's the tach itself?

Cheers.