Started it up today, no problems. I was driving around for about 15 minutes, when I noticed that the idle was getting rough and dropped from it's usual 2200rpm (don't ask), down to about 800. I pulled off the road, then I notice that the engine is 'rocking' very noticeably. If I let it idle by itself, it wants to die. I revved it in neutral to about 5000, and as I lifted, it was backfiring badly (it's never done that before), and it seems to be coming from under the passengers seat. I can't really check it properly because if I get out of the car, it dies.
I had a good look at my vacuum hoses, they seem to be okay (they were all replaced 4 months ago).

Any ideas?

Also, whent he engine rocks (to the point that the whole car shakes), what can that indicate? (I know it's not good, but would like some ideas).

 

hmm well it sounds like you have a few problems. first, your idle should not be 2200 normally haha, i know you said don't ask but really thats ridiculous. if there is backfiring it is probably your exhaust but that would NOT cause the car to die, unless there is an obstruction in your pipes thats blocking the air, but if this happened suddenly i would have to say that is unlikely. and so you know, 750 or 800 is normal for idle, so if thats where it sank down to and stopped thats not a abd thing. if you can't check it because the car idles to low now, turn the idle up, and check under the car and then fiddle with it and turn it back down.ok im out of ideas, anyone else??

 

It is possible that your cats have collapsed and suddenly clogged...However, I would imagine that you are looking at other problems, most likely to do with that 2200RPM idle. Check the standard stuff...vacuum leaks, BAC valve, cracked intake hoses, etc. Pull the plugs, crank the engine and make sure you get even pulses...Just disconnect the exhaust and try to run the car to eliminate clogged pipes as a cause.

 

Yes, this just suddenly happened. The pre-cat has already been gutted, but I guess the main cat could be shot. The idle is high because I haven't adjusted it, but it also gives me that split second to tap the gas when it looks like it might die (it happens every now and again).

I'll get the exhaust checked out to elminate/identify that as the problem.