Hey guys this has probably been asked a million times, and i have searched and read and the more i read the more I think its one thing then another... Either way.

I have a 89 Prelude Si 2.0. Lately I have been having problems with the idle of the car. My searches brought me here to HT.

Here are some of the symptoms the car has had.

1. The idle would jump from 800RPMs to 1500 when the car came to a complete stop.
*** I replaced the IACV thinking that was the problem. This helped a little but didnt completely resolve the problem. Now the car would do this on a spontaneous basis but not as bad as before ****

2. After replacing the IACV I replaced the Throttle body and TPS from one I found at the yards. These parts were cleaned and what not before install.

*** This fixed the idle at a stop. This also created a new problem. When the car was in motion and coming to stop the car would pause at 3000 RPMs on its way down or Climb to 3000 if it was below. Once the car came to a dead stop the RPMs would drop to normal. ****

3. I replaced the Throttle body one more time thinking that it was the throttle plate getting stuck. The new throttle body did the exact same thing.

4. I ordered a new TPS to see if this would fix the problem and the problem still continues.

5. I unplugged the IACV to see if that would bring the RPMs back down which it did but the car tries to stall on me.

This feels like looking for a needle in a haystack.


Either way wondering if any of you had any ideas on what to look for.


Do you guys have regional forums? I am also a member of a VW forum that uses Zeroforums so this all reminds me of home.

 

Are you setting the tps correctly? (.5v at 0%, 4.5v at WOT (roughly)

The 3000rpm thing makes me think vac leak but if it comes down when you stop I don't think so.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">Are you setting the tps correctly? (.5v at 0%, 4.5v at WOT (roughly)

The 3000rpm thing makes me think vac leak but if it comes down when you stop I don't think so.</TD></TR></TABLE>

I know you are supposed to set up the TPS but I am not sure exactly how you are supposed to do that. I lined up the TPS as close as possible to where the old one was placed but would that be the reason it stays stuck at 3K?

I figured since the Idle was OK with the exception of it sticking at 3K that the new TPS is ok and the other TPS on the other TB are also OK. I also thought maybe the IACV is bad since when the car is unplugged the idle does not stick put the car does try to stall.

I may be completely wrong tho.

 

Well have you checked all your vec lines for leaks?

What you can do is take apart the whole IM and put it back together again. Should take time, but you will know that everything is sealed properly.

 

OK so heres what I did today.

I added fuel in the car. (My gas gauge says its full all the time) With the IACV plugged in the car idles fine and drives great but the RPMs are still getting stuck at 3 grand.

With the IACV unplugged the car idles fine, but throws a check engine light. The needle doesn't get stuck at 3-Grand it comes down like it should.

Im gonna look for vacuum leaks and replace some dry hoses. If there is a vacum leak shouldn't I notice it at low idle?

 

Yes and no. It could a hairline hole. The higher the RPm the higher the air pressure in the vac lines.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Acidcrakker &raquo;</TD></TR><TR><TD CLASS="quote">The higher the RPm the higher the air pressure in the vac lines.</TD></TR></TABLE>

kinda. More dependent on load than RPM tho.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Acidcrakker &raquo;</TD></TR><TR><TD CLASS="quote">Yes and no. It could a hairline hole. The higher the RPm the higher the air pressure in the vac lines.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98vtec &raquo;</TD></TR><TR><TD CLASS="quote">

kinda. More dependent on load than RPM tho.</TD></TR></TABLE>

Sorry if I ask so many questions but... This whole honda thing is new to me so I am learning as I go.

Lets say it was a Vacuum leak. Why does it go away when i unplug the IACV? Im thinking its not a Vac leak but maybe a bad IACV I may be wrong tho and trying to fix something that is not broke. My car troubleshooting skills = The Suck.

 

You should look up how to set the TPS, and do so. Go from there.

To solve a problem, start simple, and work your way up.

 

I have an 89 SI with the same problem. I used to unplug the IACV too, to temp remidy the problem although I have figured out unpluging the TPS sensor only will help remidy this even better. Idles around 1500 RPM now. I can live with that for now until I spend some time with a meter on the TPS (I think this is the prob and maybe you got a bum one). If you figure it out let me know so I can fix mine fast....Its cold up here in Canada so I am going to wait untill the spring till I do anything!

Good Luck

 

I haven't really done anything to the car since its not my daily. I was planning on checking the voltage on the TPS but got caught up cleaning out the toolbox and buying and organizing some new tools.

I will most likely play with the car this weekend. I am going to try checking the tps settings if not I will try the other IACV and if not I will be driving it off a cliff. Actually if i end up giving up on it I will look for a Honda repair shop that can fix it. I am done trying to be a tech.

 

OK i got a chance to play with the car today.

Put another IACV and set the TPS to the correct voltage.

Still no go.

I am going to replace some Vacuum hose. I doubt it will fix it but its cheap and worth a try. Im almost ready to give this thing away... actually i'm thinking of taking it to a Honda tech and letting them work their magic.

Does anyone have any other suggestions on what else i can look for?