Misfire In My 1990 Celsior

[jonoman14]

my car has started shuddering while at idle and now also while getting up to speed....

any tips as to what this could be...i wil be checking spark plugs tommorrow and then if they

are all fine i won't know what next...ive heard some haresay about the iac valve and as i washed the right side of my engine after spilling some oil that could be something to look at as well...please help as my car now sounds horrible and i don't think i should drive it anymore as it is almost unbearable...cheers