Jumpy Idling.please Help

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Hey my car is idling kinda weird and it is annoying as hell. Ok, It idles down to about 900 then jumps up to about 3,000 then drops rite back down to 900 and does it all over again. It is so damn annoying at stop lights when everyone is looking at you and shit. Somone please help man, im confused as all hell. It is a 90 civic hatch si with a 92 d16z6 civic si sohc vtec head on it (sohc non v-tec block)
It never used to idle like this, just one day it started to decide too and now it does all the time. Help me out boys!
check your coolant level and then your coolant temp. sensor (think it is called the IAC sensor but i am not even half sure)
I kind of have same problem but not as drastic only to like 1200 or so...the mechanic I talked to today bout it said that it could be o2 sensor is throwing a bad code due to vaccuum leak or somethign of that kind, or a bad idle sensor I believe that's what he called it. Does it do it when you put the car at an idle only? because that is probably bad idle sensor where the idle is supposed to go up when you put the clutch in.
Look here hatchboy, Dan, first off you have to tell us what you've checked so far. To specify a bit further on asmallsol's comment, check your coolant level because if it's low, you'll get air trapped in your engine which cause erratic idling, and on the SI vtec head there's a bleeder at the water outlet where you can extract the trapped air. There could be numerous problems with this symptom (e.g., leaking vacuum, gaskets, injectors, etc.). Your best bet is to diagnose one thing at a time and let us know what you've done otherwise take your behind to the auto part store and read, lol. Let us know and we'll proceed from there.
Allrite you look here ,lol ;]

Heres my story and im stickin too it =x
Ok awhile back on my d16a6 stock 90 si motor, i thought i cracked my head becuase it was eating the antifreeze alive and coming out of my exhaust, and a few different mechanics told me that i had a cracked head. So i decided to do the mini me, i busted it out and put a d16z6 sohc vtec head on there with a new head gasket from the same year head and new timing belt from same head. Then It was STILLLLL allways overheating in traffic so i put in a new thermostat thinking it was that. It wasnt,so i put in a new water pump, it still didnt fix it. So it is still eating antifreeze alive and is allmost overheating on a daily bases (getting rite under the red mark on temp. guage)
It will get really hot pulling away from a stoplight then when i start just cruisin when im not accelorating anymore it will cool back down. Everytime i put more antifreeze in it i allways have that bleeder screw cracked with my car on but it just bubbles and bubbles and bubbles and doesnt stop, I sat there for 3 and a half hours once and it didnt stop bubbling and the coolant level contenues to drop, sop i would keep having to add more. This is a bitch and i can not figure this son of a bitch problem out. I have Flushed my radiator also. Come on guys help me out on this! Oh by the way, when it starts getting really hot my heater goes cold until it cools back down again if that means anything.
whats up , this is all the above that can be wrong w/ your car. listen closely and check everything.
- go over all vaccum lines making sure there is no holes or cracks
- use carb cleaner, and spray where intake manifold meets the head. if idle flutuates bad INTAKE MANIFOLD GASKET. did you change this when head was put on ?if so theyre not tightened evenly
- replace O rings on injectors ! biggy
- find good sensors from a buddy or buy a good intake manifold w/ known good sensors
- fast idle valve,idle air control valve, tps,these are notorious for this problem w/ idles. These sensors run off coolant
- expect this to be your problem expecially if coolant levels are problems. these are the only problems it can be . besides your O2 sensor which should be replaced once in a blue moon anyway. good luck
Hatchboy, my only suggestion to you now is see if anyone have done a similar swap before and get feedbacks from them. I've done a frankenstein once lsvtec, and there's oil galley that I had to plug and tap on the head to achieve what I want. What I'm saying is, how do you know for a fact that you don't need to modify your head to be compatible with your block, a D16Z6 head is a vtec you know. You should be using the same head gasket as the block not the head. From your last sentence, it seems like the problem you're having is a leaking heater core. Your heater will never get hot if it doesn't have hot coolant passing through that. Check the heater core's inlet and outlet hoses, they're known to leak after a careless swap. Check all that and let us know... Hope this helps.
make sure your tps is set at .5 volts closed and 4.5 volts wot.
I think he cracked his block.

I bet the engine is heating up so much that it's opening a hairline crack into the combustion chamber letting coolant in.

Water will combust with the air more than likely but I'm not sure about anti-freeze... it would probably be pushed out your exhaust... like you said is happening.

Not for sure, but thats what I think.
yea i did the mini me swap myself in my hatch before the ls was thrown in. i didnt tighten the hose tight enough going to my heater core allowing it to over heat all the time . even know i only drove it 10 mins after my swap and blew the si trans !!!!! haha. your actually suppost to use a 1.6 vtec head gasket and not the 1.6 non vtec. and take the oil control jet out of the block ! did you do this? if you didnt you cant hit vtec because there will be to much oil pressure. im not sure why your car is running so hot, but i told you whats wrong w/ your idle. so check it all and get back to us.
Yes i did use the 1,6l vtec head gasket and yes i took the oil control jet out. ;] , il check all of that stuff out tommarrow that you all suggested but i still think i have a hairline crack somewhere in the block sence when i start getting on it the motor will naturally heat up then that is when i start losing coolant. It is getting bad enough to where i am refilling my radiator every day. Anyone want to donate a LS for a d16a6 complete head, d16z6 complete head,si tranny,and all the rest of the motor excluding the block?Mabey some 12's and 6x9's and stuff? hmmm! ? ;]
I might be getting some Type R stuff soon also so think about that too!.
I had the same shit happeneing to me actually...except it was on a new cadillac sts, anyway, I wouldn't know anything about he head....but if you have a bad coolant connector (like a T or something) or a bad hose, it will only start leaking, or loosing fluid when the engine is revved or overheating because of a bad sensor. just my 2 cents...prolly wrong, but you should always check everything I guess.
HATCHBOY..check your TPS sensor on throttle body..Throttle Position Sensor..A few of my boyz had same problem and thats what it was..so look in to that..serioulsy..let me know if you found out or it works..holla back..
Allrite so somehow magically my car stoarted idling normal again! dont ask me how, its idling at like 600 steadely, =) so we still have to figure out the constant over heating problem. Ok here is a list of what i know and why i think the block has a hairline crack in it.

-I have to refill my radiator with coolant ever day.
-nonstop bubbles will come out when u try and bleed the coolant, or even taking off the radiator cap, bubbles just keep coming and dont stop.
-when i get on my car then turn it off then go start it again in like 15 min its bogs way down and you can smell coolant coming out of the exhaust with big old white smoke. ;] until you rev it up and burn it all out.
what do you all think? what is your final decision? =x

Hatchboy, why don't you start with a compression test and record each cylinder's reading. If you know how to do a coolant pressure test, go ahead and do that also. It's definitely an internal leak somewhere in your engine and that could mean a number of things. You might of scratched your head gasket during installation or your block is shot. But white smoke out your tail pipe is the signs for more work especially when there's no evidence of external leak, I'm assuming??? Check that out and let us know.