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Aside from the drop in engine speed, I'm also seeing a flux on the Vacuum gauge ( Which is usually dead steady at above 15 Vacuum, and is now waving from 10 to 8) and an uneven engine noise.

What my dad's thinking is that a valve broke, and a piston is misfiring. I don't really see any reason to object since we throw the car around and hold it at redline so much, but I'd like to know if there are any other theories to this...?

If it matters, the car doesn't have an oil cooler and we let the thing simply cool off after we run it hard on the track and it spikes into 150+ on oil temp.

Your first sentence pretty much confirmed it for me. When I saw the title "idle drop" my very first thought was "vacuum loss." Mainly because after fixing the MASSIVE hole in my PCV system, my idle spiked from 800 to almost 1500. I had a huge vacuum leak.

Have you already checked all your vacuum lines for brittleness or holes (or just plain missing)? I'm not sure if it applies to your car, but on my Z there's a pretty simple test for vacuum issues. You take the oil cap off with the motor running. If it keeps running you have a vacuum leak. If it sputters and dies, your vacuum is okay. This is because taking the cap off induces a large vacuum leak. If your motor doesn't want to die from that, it means you already have a massive vacuum leak, so one more won't do much.

What car do you have, anyway? I haven't really been keeping track. Then again, mentioning that you track the car makes me feel kinda silly for suggesting the simple stuff...

Drove it again, and while the idle seems to have gone up slightly, it's also starting to make alarming noises if I bring it above 3000. Apart from that, the power of it feels flat.

I'm driving a swapped 20v silvertop FF corolla. I'm not sure if your vaccum check method will work; but there's probably no harm in trying; worst I can do is stall the thing in neutral.

Moved to tech discussion

I knew I forgot something, thanks Sideways.

I'm fairly certain this won't work, as my oil cap managed to go walkabout at one point without me realising until the smell of burning oil caught my attention. The car ran fine, I just managed to have oil sprayed all over my engine bay.

My engine is a Blacktop 20V rather than a Silvertop though, so it may differ.

Vacuum leak. Check the gaskets and hoses.

We swapped the spark plugs today, and they've boosted the idle somewhat. I guess that was one problem. The problem's also been isolated to piston 4, since that plug was wet. Have yet to check for vaccum. Could I get a method?

Okay! The idle is back to normal, which I take to mean that the spark plug fixes the non firing piston.

The problem is, Vaccum is still pretty low, and for some reason the powerband jumped to 5500.
So ah... I'm not sure where I should start poking around.

Check all your vacuum lines for brittle, missing or otherwise failed hoses? I didn't see it mentioned that you'd done this. Your vacuum is low, so therefore it's leaking somewhere. If your idle is "back to normal" but your vacuum is still incorrect, chances are you have a vacuum leak and when it's fixed your idle's gonna be screwed up again (as well as a few other things, depending on if you adjusted the motor to run 'properly' with a vacuum leak). That's my only advice.

That would be the thing. I havent a clue as to which mess of pipes and wires is a vaccum line, how I would go about checking for the leak, and what I would do about said leak. I would assume though, the vaccum line is somewhere by the intake, but other than that, nothing.

I doubt we did anything other than change the spark plugs; which seems like a harmlessly routine procedure to me.

EDIT: I opened the hood out of curiousity while the car was running. I take it there shouldnt be a rather pronounced flow of air coming OUT of the general space around the intake?

This post has been edited by DigiBunny on Jun 16 2010, 04:06 AM

Was your radiator fan running?

I honestly dont know if that was the radiator, or something else. To be honest I never saw a radiator fan, so I assumed it worked by pumping air cooled water against the oil pipes. I'll check again once I get home; though dont 20v's always have a fan running right before you turn the ignition? Are they the same fan?