what engine, what transmission? ok ,no one ever knows....
gas, not diesel
tacho.read low, compared to what>? you have a hand held
optical tach? like me? or is this post just a post
saying why is my engine idling way below 800.
or why is my slushpump A/T stuck in 4th gear.?
ever scan the PCM? do so, or miss the boat (i promise)
lets say the tach reads, 2000 but my opto scan shows 3000.
the cluster brain gets tacho data , via a data buss (CAN) from the
PCM brain, so scan the PCM for errors
it can be 3 things.
1: bad tacho.
2: bad PCM , no way
3: bad comm buss. if you see scanned DTC errors for the comm buss fix that first.
Also the PCM , you connect any scan tool made to the 16pin DLC
and see live RPM, it its correct? and no comm errors?
then the I/P cluster brain is bad or gauge. (or scrambled)
id reset the cluster head power. the fsm covers this.
its the memory wire. to the head.
but resetting things can be dicey. if not done right.
The PCM will report all RPM errros.
the FSM is here. buggy it is...
id check all fuses.
id scan it
if head lies. and PCM scan shows good.RPM
id then reset the head, the fuse are OID named, (hot all time)
do you have your glove box , operators guide.
in mine on page 400 is the fuse box. see that.?
mine has 2, m13 fuse is mine. ill look yours up. now
ok its fuse #17 (IOD) IOD means ign. off, draw (old school hot all time) F17 is 10amps.
do not pull fuses in a random way
or ever pull the battery cables.
or you might find bad happens, lost radio codes and other issues
even security system goes nuts.