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-   -   LOW IDLE AFTER WARM UP (http://www.preludezone.com/3rd-gen-honda-prelude/64380-low-idle-after-warm-up.html)

Lespaul59 03-29-2018 10:36 AM

LOW IDLE AFTER WARM UP
 
Starts up at 1500 then after warmed up is basic 770. But when it's really warmed up I rev it and drops to close to 5 or 600 rpms. Curious if it's an idle control valve problem.? Anyone get this? At least it's not a high idle.

luzer 03-30-2018 10:58 AM

Re: LOW IDLE AFTER WARM UP
 
You want to adjust the idle with the engine fully warmed up. I'm not sure what you mean when you say "after warmed up is basic 770", then you say "But when it's really warmed up". What are you defining as warmed up -vs- really warmed up? Was it fully up to temp when it was idling at 770 rpms? To be fully warmed up, let the engine idle until the cooling fan has cycled on and off twice. Try adjusting the idle speed with the engine fully warmed up.

Lespaul59 03-30-2018 07:28 PM

Re: LOW IDLE AFTER WARM UP
 
After it's fully warmed up and cooling fan comes on, You rev it up and It'll drop to 500 rpms almost dying then will slowly come up to 770.

bykfixer 03-31-2018 08:48 AM

Re: LOW IDLE AFTER WARM UP
 
Got vaccuum testing kit Les?


My 5g engine was doing that and I discovered vacuum was not breaking proper when decelarating. Don't know the proper term there, but basically opening up the throttle body a quarter turn helped. I started out thinking it was the throttle cable.
I suspect it's valves or EGR but mothballed the car.

Sideswipe SI 03-31-2018 09:36 PM

Re: LOW IDLE AFTER WARM UP
 
Im with Mike, clean egr port, new gasket and if you can snag a spare egr valve in case

If there is an excessive buildup in there check for a lean fuel condition, hopefully not

Lespaul59 04-08-2018 01:03 AM

Re: LOW IDLE AFTER WARM UP
 
Noticed a crack in the pcv hose. If you notice the diameter of the connections to the actual diameter of the heated hose over the years you might have the same problem too.

bykfixer 04-08-2018 12:58 PM

Re: LOW IDLE AFTER WARM UP
 
I have a idle bounce issue in a 3G that may be caused by that Les.
I have a bunch of new hose to install at some point. Perhaps this will be the reason to finally do it. Small cracks are hard to see but can be big trouble in these cars.

Thanks for the tip.

Sideswipe SI 04-08-2018 06:00 PM

Re: LOW IDLE AFTER WARM UP
 
There is a platinum dressup silicone kit from back in the day that covers all the hoses not exposed to oil that includes the pcv, intake and vacuums so no more idle issues ...

EDIT:CHINGAS

I do not remember what ebay seller had it, but covered 3.5,4,5,6,8,10 milimeter sizes... sorry lespaul

Lespaul59 04-09-2018 05:41 AM

Re: LOW IDLE AFTER WARM UP
 
Really didnt do much but helped. Srewed in that fast idle valve and will report back.

bykfixer 04-09-2018 08:42 AM

Re: LOW IDLE AFTER WARM UP
 
:popcorn:

Lespaul59 04-10-2018 08:32 AM

Re: LOW IDLE AFTER WARM UP
 
Well, Here's the update. Ran perfect sitting in the driveway. Took it for another spin and same thing. Idle would drop down after accelerating and stumbled big time once or twice at full throttle. Had to pull over to let the idle come back to normal. Almost felt like water was in the tank. But after settling to idle drove it home. WAS wondering if it's the throttle body, cause at full throttle I had nothing a few times? it's a 5-speed. Are there any throttle body's from honda interchangeable?

luzer 04-10-2018 11:53 AM

Re: LOW IDLE AFTER WARM UP
 
I'd be more suspicious of the TPS than the TB, but to answer your question, I've read that a mid-90's Acura Vigor throttle body bolts right on. Seems strange that a 5 cylinder TB would fit our intakes but apparently they do. I grabbed one from a 94 Vigor a few years back but never tried it. Here's a thread from another forum discussing it...
upgrade throttle body found! - Honda Prelude Forum : Honda Prelude Forums

bykfixer 04-10-2018 05:31 PM

Re: LOW IDLE AFTER WARM UP
 
Are you see-ing a bunch of water spewing from the tailpipe Les? A buildup of water would cause weird backpressure issues.

In my 5g a lot of idling and short trips caused a buildup of condensation that led to some weird stuff. It was not until there was so much that I heard it girgling that I knew it was there. After blowing/boiling away a bunch of it fixed some of those issues. Unfortunately other things went wrong shortly after so I mothballed the car.

Lespaul59 04-11-2018 08:08 AM

Re: LOW IDLE AFTER WARM UP
 
Thanks Luzer! Autozone has the TPS FOR 42 bucks but gotta adjust it. Any links on the voltage readings to set it or is it in the Chiltons? I'll check the exhaust bykfixer and report. I'm guessing it's the TPS. Why would it not revv up at full throttle after driving? I had a TPS go bad on a 1990 automatic lude once. Going down a hill at idle in Neutral, the rpm's jumped way up. It sensed speed I guess and revved the engine up. Replaced the TPS and worked fine.

luzer 04-11-2018 04:12 PM

Re: LOW IDLE AFTER WARM UP
 
Search this forum and the other forum as well on testing the TPS. I haven't had to do that before, but I remember reading several threads over the years on how to adjust them based on voltage readings at fully closed and wot. It may also tell you in the Chilton's manual, but I tend to be a little distrustful of those because they cover too many models of cars and model years. I've seen instances of wrong information for 3rd gens.

Sideswipe SI 04-14-2018 09:01 PM

Re: LOW IDLE AFTER WARM UP
 
Should also adjust and calibrate the throttle wire, cause when it goes, you get erratic idles throughout the RPMS

bykfixer 04-15-2018 11:45 AM

Re: LOW IDLE AFTER WARM UP
 
Quote:

Originally Posted by Sideswipe SI (Post 809574)
Should also adjust and calibrate the throttle wire, cause when it goes, you get erratic idles throughout the RPMS

Even idle bounce in my experience. Before I learned of the 10mm "droop" in the cable (as called for in the manual or something I forget) I tightened mine thinking it was too loose and after warm got an idle bounce. I turned it back using the old clean spot on the threads and viola... issue was gone. :rock:

There is a tool to check tension and when correct there is a slight droop in the cable when idling.

Lespaul59 04-20-2018 05:11 PM

Re: LOW IDLE AFTER WARM UP
 
Well replaced TPS and runs perfect at idle. While driving it had only a few hiccups . Not bad and didn't fall flat at WOT. IDLE still dropped below 770 rpms a few times after revving. Yes bykfixer there is a lot of water in the tail pipe when warming up. Gonna adjust the throttle cable next. Then if I still have problems I'll take the fuel pump out and siphon all the gas out. Still don't know what makes it drop below normal idle after revving? My only guess is a bad IACV?

bykfixer 04-20-2018 05:26 PM

Re: LOW IDLE AFTER WARM UP
 
:popcorn:

Lespaul59 04-20-2018 10:36 PM

Re: LOW IDLE AFTER WARM UP
 
SOMETHING is allowing the idle to drop to 500 rpm's after revving and it's gotta be the IACV. What else allows idle to drop then come up to normal?

Lespaul59 04-21-2018 02:15 PM

Re: LOW IDLE AFTER WARM UP
 
Really going toward fuel or electrical. Cause when you put it in 2nd or 1st gear and floor it, it just falls flat for a few seconds before catching up. Bad FUEL Regulator? Bad ecm? Why else would it fall flat at WOT? Doesn't do it at cruise. Only when you let off throttle then accelerate. It's always getting air?

bykfixer 04-22-2018 08:52 AM

Re: LOW IDLE AFTER WARM UP
 
Like an old 1970's quadra-jet 4 barrel bogging down for a few seconds?...

Lespaul59 04-22-2018 05:19 PM

Re: LOW IDLE AFTER WARM UP
 
Hey! Still got a quadrajet on my 69 JUDGE!. Went back out and for the heck of it, Screwed the FIV down again only this time it went a little further. Almost half a turn more. Also set the TPS to be at 4.500 volts at WOT. I originally tried to get .50 to 4.50 somewhere close. Report soon.

Lespaul59 04-25-2018 08:48 AM

Re: LOW IDLE AFTER WARM UP
 
Still falls flat when accelerating. Doesn't do it in Neutral but only in gear when there's a load?Almost sounds like ignition.

Sideswipe SI 04-25-2018 08:03 PM

Re: LOW IDLE AFTER WARM UP
 
Complete shot in dark... check for restrictive flows in exhaust... like the cat and downpipe... cause if you ran rich, good chance your cat converter diededed, that would cause a blockage

Lespaul59 04-27-2018 07:50 AM

Re: LOW IDLE AFTER WARM UP
 
SOUNDS GOOD BUT AFTER WARMING UP THEN IT DOES IT. Someone online said that it might be the O2 sensors making it rich? Even when I had an O2 code years ago it still ran fine. This time there is no code? After fully warmed up, you give the gas pedal a slight touch to revv and idle drops to 500 then slowly comes up.

bykfixer 04-27-2018 01:46 PM

Re: LOW IDLE AFTER WARM UP
 
When I'm at is the point I would ask my favorite mechanic "Jimmy, wtf could it be". He'd get a big grin on his now aged face and say "let's see".... then he would set about using old school techniques to figure out what is going on mechanically (since no CEL indicates sensors are not sensing the issue). Later he would call and say "your car is ready".... so then of course my brain is pondering "well, wtf was it?"... so I'd ask. But him being near deaf would think I'd hung up on him.

Arrive at the shop and he tells me step by step 32 ways he had figured it out and by step 4 he might as well be speaking Korean... then he gets to the punch line with something like "WD40 on the distributor makes it advance proper under load now"... or some other 'holy crap I'd have never guessed that' type fix.

One time my 5th gen was killing alternators. He figured out the color coating on the inside of my aftermarket battery cable ends was the issue. Another a voltage test on each of the 6 cells of a battery showed him all 6 had a combined voltage of 12, but one of them was at 1.7 so it was acting like a dead cell. The others were like 2.2, 2.4 etc.
So I'd say it's time for something old school to check any further.

Lespaul59 04-27-2018 09:34 PM

Re: LOW IDLE AFTER WARM UP
 
Thanks bykfixer. Went to the j-yard this morn. Just got a a 1990 gold 2.1 5-speed in. Grabbed the throttle body iacv and sun roof bug guard thingy. Still said HONDA on it! Also got the holy grail. A clock with the door covering the time settings!

bykfixer 04-28-2018 08:52 AM

Re: LOW IDLE AFTER WARM UP
 
YESSSSSS

bykfixer 04-28-2018 01:08 PM

Re: LOW IDLE AFTER WARM UP
 
Les, is the car you speak of the one with the automatic?

Sometimes my rattlin' red car would act like an old quadra-jet when accelarating. It was the solenoid pack on the tranny acting up causing it to be stuck in second or third gear. It would take off fine but at mid way through the rpm shift point it would start fluttering. One day it did it. But then it stopped. I tried and tried to make it repeat but it never did that again.


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