Hi,
Lumpy idle can also be due (root cause of no spark) to other things like, over/under fuelling, timing wrong, bad compression etc
it the exhaust or plugs sooty, or wet(petrol) and sooty? (if they are, do new clean ones soot up quickly?)
is it an efi or carburetor?
what colour is the exhaust?
is there a lot of blow by? smoke coming from the oil filler cap (when removed).
what are the compressions like?
Ive just spent a lot of time getting a v8 from a classic back into shape, symptoms were similar (lumpy idle, but with black smoke), but cause was down to a ton of everything under the sun, each thing had an effect. replaced plugs, HT, dizzy, rotor, fuel pressure reg, plenum stepper, check ecu function, replaced broken throttle position pot, replaced head gaskets, honed cylinders, renewed piston rings (had a big bit of blow by, now compressions are all about 170 ish), changed bearing shells, set timing, found vacuum leaks (there can be billions of them...), replaced brake servo vac unit, replaced leaking dizzy vacuum advance, reseated valves, stripped-cleaned-tested and resealed mass air flow meter,checked injectors,checked fuel line for correct pressures, checked coil for correct voltages and that coil does not fail when it gets hotter!, cleaned and sealed plenum component parts etc etc yadda yadda...
did all of these a bit at a time and got the engine running better and better, now at a stage where it runs fine (idle is not lumpy now), but the plenum vacuum is not really low enough at idle for my taste... so i still have too much air getting in somewhere.
if your problem is just sparks or dizzy etc then that can be fixed very easily by what rangerovering says, if the root cause is something else, you could be in for a long haul of diagnosing to get the root cause.
if it is an efi, then it is easy to confuse the ecu into running the engine rich etc, all you need is a few vacuum leaks and the MAF will report the wrong thing to the ecu and the ecu will compensate by buggering up your fuelling to get the correct values i.e. lumpy idle. when revving the ecu relies more on the tps than the maf so lumpy goes away, unless the plugs are black.
Hope this does not scare you off, but this my engine has done about 130K.. or is it 180K can't remember... bugger...
Cheers,
Stephen
