this was the first sign of trouble with my bike
it then developed the droping off idle
the dealer made it worse by puting the "fix" tune in
after a rigorous sytamatic check of every main electrical componant
i found only a few abnormaloties
1. the spark plug caps did not all have a direct conection to the coil
this is what i belive was the cause of the inital 'miss fire' like you
may be expiriencing
2. the TPS voltage was not at the corect setting
after being set by the authorised triumph machanic
(this was a gutting experiance that had me stumped as to what to do
for weeks)
the remidy for No 1 is easy enough , test the H/T lead for continuance with an ohm meter and if you find an "open" lead push the H/T cable back into the spark plug cap untill it tests OK if you cant fix them then buy some replacements
i had 4 leads that tested open ( i think this condition is caused by pulling the leads off during servising)
the "fix" for no 2 is to
A, check the resistance at the plug of the TPS for a smooth
consistant change whilst opening the throtle
B, then check the actual setting of the TPS at closed throtle using
the "pin center wire" technique
my bike runs fine now and i have learnt alot from the expiriance like
mechanics don't all know the stuff we expect and pay them to,
after knowing how delicate the TPS setting is i dont use a
scrubing brush near it during a wash,
hope some of this helps