I have been having this problem with my idle for some time now with my 98 prlude. when the car is warm sometimes it idles ok at 850 then other time it idles around 1000, then other time is jumps around between 500-900. could this be the timing, or clogged injectors. i am also running rich, i get that black powder on my rear end, and i am only getting about 240 mile per tank. i think i should be getting between 300-350. i thought it might be O2 but i replaced those, then i had my injectors cleaned. could this be a timing issue, or a fuel filter?????

Thanks

 

sounds like you have a vacuum leaks somewhere that makes your idle rough..and it can also cause poor mileages..

 

All the hoses are new and I sprayed and didnt find a leak. I have also reset the ECU, and that didnt fix anything. When I come to a stop at a traffic light, the idle bobbles and then wants to die (sometimes does), and then picks back up. I also dont understand why I am runing so rich. I know it could be for numerous reasons but I have checked everything that I can think of. So I guess the injectors wouldnt be a problem??

 

Yea im having pritty much the same problem, but my car is throwing a cel code 3 (map sensor), could this be your problem? Are you throwing a code?

 

what's a map sensor?

 

Did i use the correct word? MAP stands for manifold absolute pressure. i guess the sensor is the thing that measures the MAP . any how its a little black boxy thing on the firewall just behind the throttle body with vacuum tubes going in and out of it and a plug with 3 wires coming out of it.
Any i hope this helps (i hope I've got the right info as well lol).

 

"Cincy98lude"

have you found out the problem is? because mine start to have the same problem. Got black dust on my rear bumper and idle is startin to be unstable. Thanks

 

ok we all have the dust on the rear bumper, thats h22 for you......

a new fuel filter could help the gas mileage (maybe) but not much, and it definitely wont fix your idle problem....unless it just wont let any gas through, and we know thats not the case.....

the MAP sensor tells the ecu how much air is coming into the engine by measuring absolute pressure in the intake manifold, the computer then sends in the correct amount of fuel to burn with that air.....

The MAP sensor is the MAIN component of your fuel injection control system, if its not working, you will run terrible, idle terrible, and burn more gas than the camaro z28 i whooped up on last night....

With that said, the if the MAP is bad, or disconnected, or not functioning correctly for any reason, there will be a Check Engine Light (CEL).

If you have a CEL on your 98 prelude (i assume from the title) you will need a shop to read the code out, because obd2 sucks, enough said.

So, if you have a CEL, get it read off by a shop, then get back to us.

Oh yeah, and to make sure your CEL bulb is working it should light up when you turn the keys to II. So make sure the bulb is good also.

If you dont have a CEL, then i would consider cleaning out or replacing the IACV (idle air control valve) or the FITV (fast idle thermal valve). Either of these will cause the idle control problems you are having (changing idle rpm randomly and the bouncing). But, i doubt either will affect your gas mileage.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">IACV (idle air control valve) or the FITV (fast idle thermal valve). Either of these will cause the idle control problems you are having (changing idle rpm randomly and the bouncing). But, i doubt either will affect your gas mileage.</TD></TR></TABLE>

Well yeah my gas mileage is not so good. 4 gallons wouldnt last me a day when i drive work back and fourth of 70 miles. So like you said might be the problem..but where are the IACV and FITV located..are those just some connector plugged onto the manifold? thanks

 

My check engine light did come on and I had a reading done, the obd. I know it sucks but it pulled the fuel system for bank 1 was too rich. It says the fuel compensation value for bank 1 exceeds the specified range. I dont even know where to start. I am still having that rough idle problem as well. I sprayed again and couldnt find any vacuum leaks. sometime that car dies now as well. it seems as though the problem is getting worse. when i rev the engine high and let it fall thats when it seems to want to die the most.

 

What (if any) mods do you have there buddy.
I had the same prob, the whole ("when i rev the engine high and let it fall that's when it seems to want to die the most.") bit. i have since pulled out my sfc and my string of problems has ended. Now im not assuming that you have an sfc or anything, but my sfc was f***ing with my map sensor so that strengthens my point that it could be your map sensor.
Sorry im basically just recapping what i said earlier with a bit of evidence.

 

NZludedude, did you ever try to open up your throttle to increase the idle RPM? I've noticed that I don't get the rough idle when I start on a cold engine, but the idle RPMs then is usually fairly high like 1800 before it settles at about 850 when the engine warms up.

So I boosted my idle RPM to about 1100 and it's helped a little. I still get the RPM dip when stopped at lights, but not as often.

 

Thanks for the tip, but that's more like a cover up than a fix and having little problems like this **** me off, so I would have to get it properly fixed or I'd get stress problems .
Any way my problems have ceased since I pulled my sfc out.
Cheres all the same.

 

Pardon my ignorance. But what is an "sfc?" I might try it to see if that's my prob as well.

 

Ha ha sorry, i don't even know what it stands for but its an acronym for some thing, might be, s=? f=fuel c=controller, anyway its a vtec/full controller type thinggy from Field.
So to recap, its an aftermarket device.
Sorry for the confusion.

 

Okay, since I have no such thing in my vehicle, that can't be my issue. Still searching for an answer. My buddy said this is common in Hondas, but didn't have any solution for it. I guess the next step is to clean off the IACV. I Googled a little and someone with a Camaro said his was gummed up pretty bad and once he cleaned it, his bouncing idle went away.