Possibly a different idle question?

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Justin66

Justin66

The Hondaswap Canadian
Since i bought my 98 Prelude last fall i have never driven it in warmer weather til about a month ago when its actually been hot out. The car runs well but since its been hot the idle sits a little low, around 400-500 once the car is at operating temperature. Also when its hot out the temp gauge seems to sit slightly lower than the normal spot, and thats when the idle tends to be low.

Now in the mornings when its still cool the car idles nice, even at operating temp, and only when its cool out the temp gauge sits at its normal spot.....weird. I have been meaning to get at my IAC to clean it out but this almost sounds different than it being that, however i think ill clean it anyway. You think this sounds like a coolant/thermostat thing? Could it really affect the idle? A flush perhaps...

Any input would be appreciated.

P.S i have replaced the cap/rotor and plugs just to rule out that.
 
Ok so i was driving it around town about 10 mins ago and i pretty well just proved that the idle is in correlation with the temp gauge, its not cold out by any means and the gauge for the first bit was slightly below norm and it was low idle, after a bit longer the gauge went to norm and it idled perfectly at 800. Like something is stuck.
 
hmm that is weird dude... ill do some research n c if ne one else had this problem.. definantly wierd.
 
Do you think it could be the ECU's response to higher temperature readings from your IAT sensor? Just a thought, I have absolutley no source to back that theory up.
 
Lol its a bit odd i guess. I noticed my reservoir was a bit low, so i topped up.. It hasnt been warm the last week or so, ok well not HOT anyway, so i will need another hot day to tell if it was maybe just the low coolant. Either way i im hoping to clean my IAC and get a flush, god knows how long the fluid has been in there, could just be getting gunked up. Thats the problem with used cars , you just never know.

Anymore input would be appreciated.
 
So yesterday i took off my IAC and sure enough it was dirty, cleaned it..... didnt help.

Ok get this. This morning i was driving around and it was rather cool. My temp gauge was normal and it was idling great. I got back home and decided to try something. I turned the car off and started it right back again. Now the temp gauge was slightly below and now the idle was low WTF! What does this sound like? Please dont tell me the ECU is acting up. No CEL. Maybe a reset?

This is really pissing me off.
 
Ok i pulled the 7.5 clock radio fuse to reset the ECU for 15 mins, started up and idled for a while, still low. Took it for a drive, still low idle, the car just doesnt hit its operating temperature, least the gauge says its not. Even on a hot day like today....

I unplugged my IAC while the car was running and it stalled. Also i was trying to plug up that port in the throttle body, there wasnt alot of vacuum and it didnt change the idle speed.
 
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I have the same issue with my car, but it works perfectly fine, so I stopped going crazy over it. Your car will always idle lower at operating temp. When cold, it will sit at 1.5k or w/e RPM until it hits a specific temp and drops off.

Try a new PCV valve and IAC valve?

Remove the air filter while it's idling at operating temp to see if it goes up?

Pull out the thermostat and drive it around? If you don't need heat anymore, this might just do the trick.

If your radiator was low, where is your coolant going?

Maybe the stat is sticking and a little bit is boiling out the cap, thus making something along the lines of what derek said happen?

I'd rule out mechanical before electrical.

Hell, just rig it and tighten the throttle cable a little bit lol.
 
I pretty well ruled out the IAC because when i unplug it when the car is running warm it wants to stall. Ruled out the FIV cause when its cold and i plug the hole it wants to stall and while warm it doesnt change. Switched back any forth between a honda and aftermarket PCVs. Took air filter on and off, cleaned TB with cleaner.

I just find it strange that when i drive the car and its working fine, turn it off and start it immediately after, the temp gauge is no longer at full operating and the idle is low with it. I keep shutting it off and starting it again, it idles fine for a few seconds and then you clearly hear it sink.

Could any of the sensors be cleaned like the intake temp or coolant temp sensor? I have no CEL and no codes stored, even while its doing it. The car never wants to stall but i hate it running like that.

Ill try and new themostat soon and see, im hoping its that, but i dont see how it could be making the car run slightly cooler????


And ya i know that the car will idle around 1500 and slowly lower until its fully warm but when it does its idle issue it sits at 400-500, instead of 700-800.
 
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Ok got a coolant flush and new thermostat and same problem. What would cause the car to not reach full operating temp? The fans are not on all the time either. Now this is starting to get frustrating. Still same low idle. New egr gasket too.
 
the only way ur cooling system will cause it to idle like that is if ur intake gasket port where the water goes through is leaking or ur head gasket is seeping under pressure .. mine did this.. if there is another way that coolant causes it i wanna know lol...

now about it not running normal temp , mine doesnt run normal till in 85 degree weather wo the fans on... until is park for a few min. lol i was gonna post about that n see but aint done it yet lol good luck man
 
check your timing

check to see if the ivac is getting coolant

check your spark plug gap

you can raise your idle with the screw on the tb.
 
Im pretty sure the IACV is good because when i block its port the car stalls. Im replacing the spark plugs wires hopefully tomorrow, im hoping its that, the car drives just fine, maybe at idle there isnt as much spark energy making it run bad. Wont know til tomorrow.

The timing belt was done 8000k ago so timing shouldnt be off.

Monday i plan to take the TB off, clean it out good and replace the gasket.

Im hoping it has nothing to do with the head gasket.

I looked briefly for a vacuum leak and couldnt find one, blocked off the whole TB with my hand and it stalled, isnt that a good thing?

What about cleaning the MAP/MAF sensor?

Slowly going through the list....
 
try bleeding the coolant system, since u already flushed it, could be some air left in it...there is a bleeder valve next to where the upper radiator hose connects to the motor, and a little valve pointing up. with the car running, loosen the valve just a little, enough for coolant to squirt out a little, not for it to pur out. when u see coolant squirt up, tighten it, wait a few secs and repeat, keep doing it till it soesnt squirt a stream of coolant when u barely open the valve. and make sure your radiator cap stays on while u do all this, to pressurize the system, cuz if u leave it off, opening the valve wont do anything.
 
I have tried that a few times, its got be either a vacuum leak or maybe a fuel problem. Once again the car does DRIVE fine, just the warm idle is nasty. When i put the clutch in while driving, the idle bounces off the 1k rpm and them will slowly drop down to 400-500 and sit there, slightly fluctuating.
 
after checking all that it has to be a vacuum leak... oh btw did u check the pcv valve? the hose under the intake? i had a vacuum leak there on mine...
 
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