alright well i have a 1990 Honda CRX HF, the car is not stock recently had a sohc ZC motor swap. I have been having this problem ever since i got the car. when i start it up the car idles at 2k rpm, now when i start driving and the car gets warmed up the idle bounces from 2k down to 1k and when it would drop it would sound as if i turned the car off but it would start up running at 1k and back up to 2k rpm but as i put it in gear and start driving it and i push the clutch in it would shoot up to 3k rpm and sit like that for about 30 seconds, then it would start doing the rpm bouncing. I thought it was an IAC Valve problem, So i took the Iac Valve off and cleaned it out with carburetor cleaner and put it back on. but then again it still did it. So i spent $150 on a new Iac Valve and put it on and what do you know it was still doing it. So i then looked at other problems i started messing with the vacuum lines and wallah it was fixed it ran fine and didnt have any problem. then I had a z6 VTEC head put on and when the guy who was helping me install it started ripping out all the vacuum lines to get the head off well sure enough when we get everything hooked back up and the car running it started doing it AGAIN and my mom and dad are extreamly mad about the idle. I tried messing with the vacume lines like i did before but nothing has changed. SO CAN SOMEONE PLEASE HELP ME!

 

bump

 

i have the exact same problem man and it seems like the problem is unsolvable... i been tryin to get it to go away for like 3 weeks now and it seeems like there is no out.. imma keep searching but if you find n e thing out please let me know

 

me 2

 

try cleaning out the FIT valve. its located directly under the throttle body...

to see if you have an iacv problem you just simply unplug it when the idle is bouncing around, if the idle smooths out or goes down to normal clean/replace the iacv.

while you have the FIT valve off see if the screw inside is unscrewed too far, screw it in some and make sure the gasket is in good shape.

also if you added coolant reciently you may need to "burp" the coolant system.

use the red button in the top right corner.

 

same problem with idle up and down 1990 hf with i think a 95 94 head 16 vale i think and hf intake and si tranny so i cleaned the iacv and replace with one i thought would work car drives alright tell it warms up the it goes into limp home mode and barly drive what the hell???????????/