Why does my car misfire?

so have you watched under hood when this happens to get an idea what is causing it?

Lets check out this guide to help us fix it

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

is the check engine light on when running? get codes read if it's drivable.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

I have a 1999 Olds Intrigue and it threw a code for a misfire in cylinder 3 I've changed all the plugs and left the plug boots because they looked fine I was wondering what else the problem could be

I have heard that the coils rarely go bad and I am definitely not wanting to spend the 230 dollars to replace them so any help will be appreciated thank you.

hi which engine do you have?3300 3.4

Its the 3.5 liter

try swapping coils and see if problem moves with it?

check engine light blinking engine misfire?

Flashing light indicates catalyst damaging misfire. Is it running rough? Lets get the codes

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

and

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please run down this guide and report back.

yes and now a security light is on

Correct the misfire, and the light should stop blinking. Don't know on the security light, it should not be related.

what causes the misfire or where could i start looking

It is going to be a time saver if you can first determine what cylinder it is occurring on. Is this a 3.5, or 3.8 liter engine. Your misfire can be from a spark plug, fuel injector, plug wire, coil, or an internal engine fault(broken valve spring, follower, valve,etc..). By finding out which cylinder is the problem, you focus on one cylinder. It may set an individual cylinder misfire code that could narrow it down, or it could have a general misfire p0300 only.