idle/computer problem... - Honda Prelude Forum

99Prelude_LC · 05-15-2001, 03:56 PM

Well I replaced my o2 sensor last week, and i reset my ecu of course. Anyways with the fouled o2 sensor my idle would stay low, like 400RPMs at random times, but as soon as i put the new one in it adjusted back to its normal idle at around 750/800 mark on the tach. However when the weather is warmer outside it won't adjust, it just keeps falling to 400rpm. I tried reseting in that weather condition but it didn't work.

Should I manually adjust my idle up? What doesn't make sense is that its okay while its cold outside so I don't know how that will affect it. any suggestions would be appreciated.
-Guy

chim15 · 05-15-2001, 05:24 PM

Guy,

I've been experiencing the exact same thing for some time now.

I've tried everything - checked all the vacuum hoses, check the Idle air control valve, changed the ignition coil, etc, etc, etc. - and the only thing I can say is OBDII sucks ass.

I've been experimenting a bit and come to these observations. THe idle starts screwing around, as you said, only during the warmth of the day, at night it's pretty much fine, right. Mine will drop down to 550 or so every now and again at stop lights and whatnot and I can feel a slight vibration in the steering wheel at idle. This all started happening after I began modifying the air parts - i/h/e. Also, I notice that when I take off normally from a light, the car seems to hesitate and the RPMs drop lower than normal, not bad, but noticeable to the point that I've actually killed it, which hardly ever happens.

However, the last few days, I've been resetting the ECU intermitently. I'll let the car warm up and make sure it's exhibiting the stuff I've been seeing - low idle, power loss, etc. Then I'll reset the ECU by pulling the fuse for like 10 minutes and start her back up. Immediately after doing this, the car runs fine, idles solidly and is strong. Then after about a day, the symptoms are back. This leads me to conclude the ECU is retarding ignition or altering the fuel maps or both for some reason. After checking the solidity of the ignition and vacuums and stuff, I thought that maybe the O2 sensor was screwed and this might be the case. But after contacting several people on the TOO board about the same problem, I've pretty much ruled this out, not to mention that my car's never thrown a code.

I hear about OBDII being restrictive, but I don't really understand how the system works, so I can't fully comprehend the mechanism that would cause this.

Sorry about the length of this post and the fact that I haven't really forwarded a solution, but hopefully someone can shed some light on how OBDII works.

I'm seriously considering Marcucci's OBDII workaround.

Also, I've heard the computer system on the 99-00-01 Preludes is slightly different than the 97-98s, but I can't remember where I heard it or what that difference is.

More and more, I'm consdiering an OBDII-OBDI swap.

Ed

99Prelude_LC · 05-15-2001, 05:55 PM

Ed -

thank you for that post, its good that it was long! I noticed exactly waht you were saying. However my o2 was fouled and replacing it did gain me a ton of low end and top end power back. I'll post a pic of my o2 later tonight so people can see a fouled o2 from an exhaust leak.

I believe you're right in the obdII computer, I think because i neglected the problem for so long due to the fact i was waiting on a header to do the o2 all at once but finally gave up, the OBDII computer has become accustomed to the settings. If theres some tech knowledgable people on this computer that would be great. I think over time it will just return back to normal.

You had an exhaust leak too if i remember correctly from that email yes? I'm going to install my v-force tommorow. It alters timing, air/fuel mixes directly from sensor readings and i'll see if it tricks the computer into the right settings. After this i'm all outta options just like you. Keep me posted if you find any information elsewhere. Thanks

VPuppy · 05-15-2001, 07:24 PM

hey its a long shot but you guys should check this out

http://tech2tech.net/library/shared_htm/thrmhtst.htm

hope this helps.

VPuppy · 05-15-2001, 07:34 PM

or this

http://www.preludeonline.com/showthr...threadid=22726

chim15 · 05-16-2001, 07:44 AM

Vpuppy,

That second link didn't work, could you try reposting? Thanks for the first link though, it had some good stuff in it, but I'm not really exeperiencing any problems starting the car when it's warm. And if that went bad, it would eventually throw acode, wouldn't it?

Guy,

Let me know how the V-Force works. I also visit the Endyne board and a guy posted there saying he had simply respliced the O2 wires to bypass the connector harness because it was so filthy he thought it was screwin with the computer. I also was thinking that the intake air sensor was going wacky on me. I guess the only thing to do is keep driving the thing until it throws a code, as none of the Honda shops around here seem willing to work with me on this. They're all saying, "No code, no clue."

BTW what mods do you have?

Gundam Zero · 05-16-2001, 08:41 AM

Just wante dto see if I could help:

1. Have you tried getting a valve adjustment lately, sometimes for redlining alot you need a valve adjustment more often. have your valves adjusted usually removes some of the sloppyness that you engine had before.

2. About you car hesitating, Well in hot weather at stop light you have to remeber that you car is just sitting there with no fresh air under the hood. All that you intake is breathing in is hot air from the radiator. This will cause you car too hesitate and hiccup when you take of from a lower RPM. Also if you ever notice when your car is at idel and your fan or air conditioning is on, or if you brake is depressed, light are on or stereo is pumping the RPM of your car will drop. That is normal.

3. I wouldnt worry to much about OBDII.. Its not that bad. If you need to reset you computer, just make sure that your car is already warm. Take of the battery or fuse for at least ten mins. After 10 mins, reconnect everything, and start the car. Let you car idle for 5 to 10 mins ( make sure you do not hit the accelerator, just leave the car alone).

I hope that in some way this helps. This was a problem i had with my integra and civic (prelude now). peace

chim15 · 05-16-2001, 08:49 AM

After reading through numerous posts, I'm beginning to thing that maybe the it's more related to the air-fuel mnixture than anything. Is it possible that with the increased air flow, the computer is sensing a lean condition and dumping more fuel at idle, causing a rich idle condition, which would explain the bogging and idle fluctuation, especially since I only noticed these things after upgrading the air flow components.

If so, how can I lean out the idle fuel delivery? I was thinking of getting a V-AFC or something. Would a fuel pressure regulator work? Probably not, as the computer is calling all the shots, huh?

jbx · 05-16-2001, 08:53 AM

You know what, I have a VAFC. I try leaning it out, and still on my a/f gauge, it indicates rich.. I'm guessing OBD2 compensate the changes u made. Oh well, I just buy the VAFC for VTEC x-over and use it as a chick attraction tool..

99Prelude_LC · 05-16-2001, 09:43 AM

ugh, i hate that no code no help BS. But i have a feeling is an air/fuel mix thing also in combination with the OBDII.

I had my valves adjusted 6k miles ago. granted i redline, they're still pretty good. I'm the type that needs them adjusted every 12-15k miles i'm sure

right now the only mods i have on my car are cold air intake (akimoto), catback exhaust (greddy PE), and me as the driver

On the low idling in hot weather the vibrations are minimal compared to when i had my bad o2 sensor so i think its adjusted more but the tach is still showing less than normal, its hard to tell. I wish I had a vafc to show rpms to see where it was really at.

As far as chick magnets, the dolphins on my pioneer 7200 handle them Quite well

GoBabyGo · 05-16-2001, 01:33 PM

If you go to www.ntpog.com there is a section I believe on installing the VAFC, and in that section they also talk about putting a switch in line with another wire on the ECU. The wire apparently keeps the obd2 from resetting to factory settings. I'll see if I can find the exact page and get back to you soon.

VPuppy · 05-16-2001, 06:26 PM

chim15,
I don't think that would trow a code seeing that the site says nothing about a code for the fuel system being trow. i could be wrong though. if someone could call the dealer and ask if a bad ECT would through a could that would help.

i think its a air/fuel problem too. since OBDII used 2 o2 sensors you should check the other with a multimeter and see what resistance you are getting.

from the first link i posted it said this in the article:

"The problem is when you cut the car off and do a restart. When the ECM "sees" a start signal and a cold signal at the same time it increases the injector PW from the normal running width of 2-3ms to as high as 100ms. A hot engine typically can not handle this much fuel, and the engine floods."

i think that something similar is happening to your cars. if i were you guys i would go through the DIAGNOSING section of that link and check out your ECT sensor. i know this may not be the problem but its a possibility. that same page is linked to two topics:

PGMFI - The car is running rich and seems to be sluggish

All Models - The car seems to flood after re-cranking hot

also the second link is to the fourth generation page on this site(preludeonline.com) entitled "Starting Air Valve on 4th gen (sorta long, not too much)"

Starting Air Valve on 4th gen (sorta long, not too much)

the post deals with aftermarket intakes and a vaccum line that is left hanging after the install because the new intake does not have a port for it.

sorry for the long post and if i seem to be a pest about this but i think this is extremely close.

chim15 · 05-17-2001, 07:29 AM

Yeah, for now, I've been simply resetting the ECU every couple of days and that seems to cure the problem, but it slowly creeps back as the computer relearns. But I do have an ohm/voltmeter so I might try testing out the ECT, O2 sensors, IAT, etc., etc.

Like I said, I think the computer is overcompensating for the increased air and causing the rich idle. But i also suspect that a faulty O2 sensor or ECT or IAT, but not faulty enough to trip a CEL, may be exacerbating the problem. And I've seen a couple of other posts here, actually the old H-A.net, where people have been getting more or less the same thing and have simply adjusted their idles. That's not really a route I want to go, as I'd rather find the true issue.

I also was thinking of getting a V-AFC or something, but I don't have the coinage yet. I've also been considering a fuel pressure regulator. We'll see what happens.

Thanks for all the good info and stuff. I really very much appreciate it.