Misfiring - again

I took my GTA out today for the first time in several months. The last time it was out it behaved itself. I have had a misfire issue in the past but it seems to have been sorted.

Anyway, once warmed up & the car seemingly running ok. It decided to misfire when accelerating. Gentle application of the accelerator was fine, but when pressing a bit harder, there it was, together with the speedo fluctuating, which again I thought I'd sorted.
My first thought was damp in the distributer but the car has been kept in a dry garage, & that shouldn't affect the speedo anyway, should it ?? My next thought was bad earths. Could this be the problem ? where about is the engine to subframe earth please ? & is there a main battery earth feed to the rear subframe ? or is it earthed through the chassis backbone to the battery ?

Cheers .

[stephendell]

Still worth checking the dizzy cap as they can mysteriously condensate.

There is a technical bulletin which includes several earth additions. Will
See if I can find it and photo.

A couple of years ago, my atmo had a misfire at around 3500rpm. Solved by fitting a new ignition control module (the correct original Bosch one). Found it, via Ebay, through a supplier in France.

Thanks for the feedback. As Stephen knows, my car is an early one - 1986. So it might benefit from the revised earth set up.
Anyway, I replaced the ignition module last year, & I have regularly checked / replaced the dizzy cap. I think that condensation is the culprit. I did look at replacing the dizzy drive oil seal as suggested some time ago, but its far from straightforward. Maybe a good run will sort it.

My misfire was solved with a new distributor cap and or brush - something about a worn brush causing the problem, I seem to recall.
Regards

[pgoldsmith]

May be worth checking the idle air control valve?
I believe mine occassionally sticks (open I think) especially if I havent used the car for a while.
I think it can cause hesitation when the car gets warm and a rough idle.
Take it off, spray some carb cleaner inside and it seems to help.

Also, check the connectors going into the ignition module. I disconnect mine, spray switch cleaner on the contacts and re-fit.