Idel jumps a full RPM - Honda Prelude Forum

2PhastPrelude · 01-27-2004, 01:04 PM

full as in 1000 rpms

went out riding around with a friend and decided to run the car alil went through the gears shifted to 3rd and heard a pop, like a back fire... didnt really think anything of it other then haha must of blew a flam from being rich and having a test pipe. Well when I stop the car at a light after that the idel was jumping from 800 to about 1500.... thought it was strange but went home and parked the car and let it sit overnight till I could look at it better. The next day I went out and started it and the idel was jumping alot more

when the engine is cold it jumps from 1000 to around 3000 (for about a year now if I drove the car when it was cold or I had just started it and not let it warm up any the idel would jump like that till it did warm up, then it would idel fine no problems)

when its warm it jumps from 1000 to about 1800. the idel never drops below 1000. Except about a weekago I left the car running at a car wash to wash it, after about 30 mins the idel just stop jumping outta the blue and stayed at about 850 rpms I thought I must of un froze the ICV or something, but to my suprise after driving off it started jumping again at the next stop.

a few weeks ago I took the ICV off and cleaned it out after searching on here and seeing that was the cause of somepeople having this problem. Well it had some carbon build up on it and everything, si I cleaned it out really well with some carb cleaner, let it dry out and then put it back on.... still the same.

Today I decided to "grow a sack" and try to bleed the coolant like Ive have 2 people tell me to do. I go outside start the car and then open the bleeder valve thats by the coil, hold the revs to about 3 grand give or take alil and keep it open till I get a steady stream of coolant. I started to get my hopes up because for a few secs no coolant came out and then alil then it stop and it kept doing that. Well when I finally got a steady stream I closed it off and then let go if the cable to the TB, the engine still had a jumping idel. So I sut it off refilled the coolant and then started it back up and tryed again (3 different times) and still the samething, never got any better or any worst.

Well after talkin to a friend that I trust, he said to try lowering the idel.... So I let the car warm up for 10 mins the coolant gauge was in the middle like it usally is when the cars warm and I turned the idel screw out as far as it would go before it started to get tight, and nothing. So I turned it all the way in and still nothing, I put it back to where it was before so I would have any problems.

I decided to unplug the ICV and see what happens, as soon as I did the car started missing and running like **** but the idel wasnt jumping, I pluged it back up and went ot go shut the car off and it had thrown a cel. So no big deal I caused that to happen I shut the car off and turned it back on and it was gone and the car had the idel jumping again but didnt sound like crap (the cehck engine light went away with out reseting the computer)

Im outta ideas....... I hope someone else can tell me if Im doing something wrong or if theres another way to help this

red92si · 01-27-2004, 01:51 PM

What you want to try is releasing trapped air from the cooling system. Just pop your radiator cap off for 15 minutes, and that should let any air bubbles float to the surface. I had the same problem a year ago after I had my radiator flushed for a routing service. Icouldnt figure out why the idle was jumping. I cleaned the IAC and all.. It turned out to be some trapped bubbles from when they refilled my coolant. No probs since.

2PhastPrelude · 01-27-2004, 01:59 PM

leaving the engine off or on? cold or warm?

red92si · 01-27-2004, 02:07 PM

Engine off... cold...

you wouldnt want to open up the radiator with a running or hot engine... fluid would spray and burn you.

racinghonda · 01-27-2004, 03:03 PM

Try checking to see if your throttle cable is not snagged on anything. Flick the throttle rotor (on the TB) and make sure it snaps shut. It should snap shut againts the stop.

I had a problem with a bouncing idle about two month ago because my throttle cable was slightly out of its normal path which caused it not to shut 100%.

2PhastPrelude · 01-27-2004, 03:11 PM

tryed both neather worked.... left the cap off for 45 mins just to be sure and then let the car warm up after about 20 mins sitting the car still jumped from 1100 to 1690 on the vafc

the cable has some slack in it, not alot but enough that its not that, and the throttle rotor is sitting where it should be, the screw and nut that holds that all up still has the paint line on it thats strait and matches up

I donno what else to do.... anymore idea?

Tony · 01-27-2004, 03:22 PM

my friend had a similar problem and his tps sensor on the TB was loose...he just figured it out today.

2PhastPrelude · 01-27-2004, 03:25 PM

nope not it eather unpluged it and pluged it back up and still doing it...... thanks for the help guys

keep em comming Im will to try almost anything not to have to take it to honda

alphajesse · 01-27-2004, 03:34 PM

try a known working IACV from another lude

2PhastPrelude · 01-27-2004, 03:41 PM

had plans for that but the soonest I can get ahold of one is next week

Tony · 01-27-2004, 04:49 PM

Quote:

Originally posted by 2PhastPrelude
nope not it eather unpluged it and pluged it back up and still doing it...... thanks for the help guys

keep em comming Im will to try almost anything not to have to take it to honda

no not as in the plug but the actual unit was screwed in loosely

ludebeginnings · 01-27-2004, 07:06 PM

back of the throttle body (firewall side), on the intake side of it, there is a plate with two small screws that can be loosened off. It's about a quarter in diameter. Undo the screws and tighten the white plastic piece underneath of it. FOrget what it is called, but from what I hear it is a major source of idle jumping. If you want, when the ice melts I'll come down & show you where it is at - I found it a few days after we left Mike's.

Vapor · 01-27-2004, 07:40 PM

that SOUNDS like you're talking about the fast idle thermo valve.

screw adjusting it. just yank that thing off. do the coolant bypass mod. put a plate between the valve and the TB. viola.

for more info on the bypass, IAC bypass...

as for blocking off the fast idle valve, pull the valve off the bottom, trace teh valve onto a cereal box (yes, I'm serious) and place the cereal cutout between the TB and the fast idle valve. don't do this without the TB coolant byapss though.

Vapor · 01-27-2004, 07:47 PM

also, sometimes with the coolant thing.

you need to fill it, run it a bit, fill it, run it, several cycles before you get all the air. I hate that bleed fitting, it's never worked right for me.

Vapor · 01-27-2004, 08:04 PM

oh and check the PCV valve. it should rattle. it might be jammed.

2PhastPrelude · 01-28-2004, 12:42 PM

coolany by pass fixed the problem..... it was the fast idle thermo valve that was causing the problem... the white plastic piece that ludebeginnings was talkin about was completly unscrewed.

But like Vapor said, While I had everything off I did the coolant bypass and it fixed the problem, and maybe picked up A hp.

THANKS GUYS!!! The allmighty Vapor and ludebeginnings