Idle Problem - Pulsing Idle - Honda Prelude Forum

vipastyle · 11-01-2004, 05:22 AM

I cleaned my IAC valve, but still have a pulsing idle. It's strange... If I hold the VAFC throttle percentage at only 0.2% it will stop, but whenever I totally let off the throttle, it will pulse from 1200 to 800. It goes up to 1200, holds for a sec and drops to 800 and goes right back up. Also, in the morning when its cold and the idle is higher, it sometimes does it still. Goes to 1900, drops to 1200 or so and back up. But if I hold the throttle very slightly on the VAFC at a small number that shouldn't matter, it will stop. So maybe its electrical? Not sure. Anyone have an idea?

Thanks in advance!

Tannie

dublued · 11-01-2004, 06:14 AM

i had a similar problem, but was never able to find out what it was. I had cleaned the IAC on multiple ocsassions and adjusted the TPS sensor, but nothing had seemed to help.

could be your wiring from your ecu?

prelude2005 · 11-01-2004, 06:17 AM

No CEL?

Demonlude · 11-01-2004, 07:11 AM

I've also got this problem at the moment. Could be the fast idle valve that needs replacing (it's around the throttle body somewhere).

vipastyle · 11-01-2004, 06:26 PM

Hmm I'll check it out by swapping with a fellow 4th gen'er.

I get a CEL after coasting for a couple minutes at around 2-3k RPM but the previous owner says its from the EGR valve, theres no actual malfunction, and it resets itself and turns back off everytime I turn the car off.

Lucke · 11-01-2004, 06:43 PM

tannie, do a search... its a very common problem with JDM H22's... and the thing that sucks is that nobody knows how to fix it.

rayslude · 11-11-2004, 11:00 AM

you might need to adjust the tps (throttle position sensor) on the back of the throttlebody... just a thought

ZIG · 11-19-2004, 06:22 PM

how do you adjust the TPS?

Lucke · 11-19-2004, 06:33 PM

the TPS is only adjustable if you have a JDM H22. its tightened with some T10 torx screw, and should be adjusted to .45V (or is it .45A?) either way, its easy to adjust, but its a pain in the ass.

most likely thats not the issue though. it might even be a EGR issue, but i'm not sure.

4thGenReady2Go · 11-19-2004, 07:39 PM

another possibility (not as likely, but worth a shot) is that you have some air in your coolant system. Bleed it and see if that doesn't fix the problem.

Dallicis · 11-20-2004, 11:50 AM

willing to put money on it being the fast ilde thermostat valve... Located just under the throttle body... Seems to be the time of year when its use becomes important as temperatures change, yes even in Texas.... Usually a pulsing idle is caused by this common problem... Its just plain worn out...

Mingosh · 11-21-2004, 07:06 AM

I had this problem with my Prelude when I eliminated my egr. I'm lucky that I don't need to worry about emissions where I live, so I just blocked it off. When I took it out, I got a surging idle, but only when the motor was cold. After it warmed up, I didn't have any more idle problems. Hope this might help.

ZIG · 11-21-2004, 09:04 AM

i believe it's an electrical problem. this because i had to pull my Odessy battery (don't get one, it won't hold a charge in cold weather) to charge it, and came across a bare spot in the tie down. there was a spark. i checked all fuses and everything worked fine. the only difference is that it started to surge when warm....again. (still don't know how it disappeared last time)

Dallicis · 11-22-2004, 11:12 AM

ok.. take your intake off.. Now, crank the car up. let it warm up. Is it pulsing? If yes, look inside the Throttle body. Theres 2 holes on the inside of the throttle body on the backside where the firewall is. Cover the lower one with your finger. Still pulsing? Cover the top one with your finger. Still pulsing? Then, its electrical, IAC, or IM is lose.

mtbprelude · 11-23-2004, 10:20 AM

Tannie- You live in Houston, you have no need for the Fast Idle Valve, even in the dead of winter. Do the coolant bypass, seal the Fast Idle Valve, and the problem is gone.

For people in the north, a new fast idle valve is the best solution, and they are relatively cheap.

prelude2005 · 11-23-2004, 11:10 AM

I've done the coolant bypass, and I have a slight idle problem, it revs from 1000 to 1200 on the VAFC, but it only does it once in a while. Then sometimes it will pulse and then drop to 900 and stay around there...

Then somedays it's just normal idle 750-800rpm

anyone know?

Mr.Badguy · 11-23-2004, 03:05 PM

IMO its probably the tps. Its actually easy to just replace the whole thing. But, I dont think honda sells it alone. But there is a trick to this. Just go to a junkyard or find a dead honda somewhere that still has a tps, it should still be riveted to the throttle body. just unbolt the throttle body so you can hold it or put it in a vice. just take a hacksaw to the rivets just to where you slice them so you can unscrew them like a flathead screw and viola! You can usually get quite a few of them for pretty cheap at a junkyard because they are so small. Its good to get more incase some of the ones you get are busted.

Oh yeah and theyre the same on all hondas so it doesnt matter what car you get it from.

Absolut · 11-25-2004, 12:29 AM

I had this exact problem after the JDM h22 swap... But I adjusted the TPS and it was all good after that.

FWIW I was using the Si throttle body on the JDM motor cause the JDM was was damaged in shipping. The Si and JDM H22 TB's are the same part. Both adjustable.

boostedlude92 · 11-27-2004, 08:40 PM

anyone try adjusting their tps sensor besides him yet and get this to work?

boostedlude92 · 11-28-2004, 06:08 PM

here is a link to my post on H-t i fixed my idle surge this way.

http://www.honda-tech.com/zerothread?id=1069005