i installed my 5" proform tach, it seems to run a little uneven, all connections are right. it will run smooth for 500rpm then jump then smooth..etc, and on the tach it idles around 1100ish? on factory its like 600? is my factory tach that far off? or is my new one not working right?
i bought it used

if anyone has the same tach! i need the part number!
(in my avatar) proform 5" with shiftlight, and recall

i dont have the factory shift light on mine tho.

 

Yes your factory tach can be off by that much, if someone hooked the tach up incorrectly they could have damaged it. I have repaired some in the past AUTOMETERS mostly, they should all be similar internally. My tach had a bad diode on it, I replaced it and a few of the capacitors because I was in there anyways and had them lol. That was 10 years ago and now its in my dad's GTO with no problems at all.

 

is the switch on the back of the new tack on the 8 cyl side

 

theres no switch, its strictly for 8cyl only, if you want 6 cyl cut brown wire, if 4 cyl cut brown and yellow

 

my tach did the same thing and it was a loose wire i had connected to my coil. it would work fine and then start jumping. also i dont know if it matters but in my 79 the idle is around 1100 and 800 in drive

 

my 1100, 1200 idle seemed high. my father is getting a peice off of our friends mustangs, my father pointed to what it is (it was on the throttle body i think) and he said it will fix the idle? i dont know..

 

dc_mann8 was the thing he pointed to on front of the TB? If so thats the idle air bypass valve. Unless you are getting the new one for free from your friends stang just take your old one off and clean it out. 2 bolts hold it on. There is a little plastic float inside that should be white but I bet yours is black. Spray some carb cleaner in there and your all good. When these get clogged they can cause a rough idle but Im not so sure it will fix your fast idle.

 

yes it was on the front, it must be it, and i am getting it for free

 

you might try hooking up the tach sensor wire to the other side of the coil to see if this makes it work correctly. and make sure the tach has a good ground connection also.