RPMs too low for car life

[WilliamW]

Ok, so this is what I've got. It's a F22B DOHC non V-tec out of a prelude Si along with the 5 speed transmission. Everything works fine except for 2 things. My car runs rich. AND it wont idle properly with out a vacuum leak in the manifold (which I let there).

Heres the details. My car runs rich according to my NON wide band O2 sensor hooked up to my NON wide band Air/Fuel ratio gauge and my computer keeps throwing a code 43 I believe. The code is for the "fuel supply system" code. I've replaced my O2 sensor and the old one is always black with soot. I don't know if this is related to my next question or if it's in the tune I have. If it's in the tune then I guess it's looking like a good time to get my car dyno tuned. But I want to fix this next issue before I do that.

My second Issue and most important is my idle. I hooked everything up and made sure I have no vacuum leaks. It idles but roughly and pretty low. When I give it gas it takes off, but if I take my foot off the gas pedal the RPM's go down and when it hits the idle point it just keeps falling down until the car dies. Each and every time i rev the engine it dies if i let it get too far down. I was looking into the IAC for the problem and i'm not sure what's going on. taking it off the car I cleaned it out and it really didn't look to bad. There was carbon build up around the inlets and I used choke cleaner to spray out all the dirt and air blew the IAC dry. Testing the operation we supplied 12v. to the terminals and the thing snapped open and closed very quickly. Assuming it was good I put it back on the car and turned on the car. Still it died when I gave it gas and let the rpms fall. On the cord the voltage output is at about 13.5 V.

Taking the IAC back off I decided to watch for the operation of the device myself. I put my fingers over the inlet hole on the manifold and regulated the idle myself. As I choked the engine for are or gave it too much I was watching for the IAC device to be moving around even a little bit. But nothing happened. I really don't want to buy a part for my car if I really don't need it.


Does anyone have any ideas why my car's acting funky? Thanks Guys!

[johnl]

Have you set then idle speed with the brass screw on the throttle body?

Disconnect the IACV then turn the idle adjuster (on throttle body) anti-clockwise until the car will idle. Then set to spec idle and see what happens when you reconnect the IACV.

Personally, I reckon the IACV is much more trouble than it's worth (causing problems associated with gear shifting that affect driveability, even when the IACV is working correctly). I've blocked off the ports into and out of mine, then set idle on the high side of spec so the car doesn't vibrate too much when the AC is used. Much better gear shifts (makes no difference for auto).

[WilliamW]

Really? huh.... You don't have any problems idling? I'm going to look around here and see if the removal of your IAC is doable without any major consequences. I really like taking off as much as I can without losing any power. Comfortability I don't really care about. But as long as it runs fine and idles fine, I'd be perfectly happy removing my IAC.

I'll go and try the adjustment though. I'll let you know how it goes.

[WilliamW]

Well, I tried that screw on the throttle body and that didn't do too much. My car didn't die immediately after I cover the vacuum leak. but it didn't run right either. It runs low still and when I rev up the engine and let it fall down theres a slight knock. Kinda like
rev... rev... rev... REV REV REV rev rev rev rev. rev.. rev....rev....... (knock) rev ...rev... rev...


but with the idle open and the vacuum leak still there my RPM's are a bit higher and the engine runs smoothly. Still dips down a bit with the vacuum leak too though but not as bad and I don't get that slight knock.

[johnl]

If turning the idle screw out makes no or little change to idle speed then the idle port in the throttle body may be blocked with oily / sooty crap. I suggest removing the throttle body and cleaning it thoroughly with carby cleaner (aka throttle body cleaner). You want to make sure that both of the little ports that by pass the throttle plate are clear.

[johnl]

Really? huh.... You don't have any problems idling? I'm going to look around here and see if the removal of your IAC is doable without any major consequences. I really like taking off as much as I can without losing any power. Comfortability I don't really care about. But as long as it runs fine and idles fine, I'd be perfectly happy removing my IAC.

Don't remove the IACV, nor disconnect the electrical connector. Either of these things will cause problems, the ECU won't like it.

You can blank off the ports into and out of the IACV with some shim (drink can aluminium is perfect). When you do this and leave the electrical connection in place the ECU won't detect that the IACV isn't operable and thus won't throw a CEL and won't interfere with the engine in any other way (try just disconnecting the electical connector and you'll see what I mean).

With a disabled IACV the idle rpm won't adjust to additional loads on the engine, so you need to set the base idle speed high enough so that when auxilliary loads are placed on the motor (AC, lights etc) the idle dosen't drop so low that the car vibrates harshly.

[WilliamW]

Ok, so I blocked off my IAC with a piece of metal I cut out from my work. With the vacuum leak it runs pretty good. RPMs are around 900 and no major RPM drops after throttle (maybe down to 750 then bounces back up).

However when I close off all vacuum leaks the RPMs go down to about 550-600 and runs fine when I have my foot on the gas but when I let it off it dies out most of the time.

I've tried adjusting my distributor, nothing.
I've tried adjusting the idle mixture brass screw, nothing (it's out all the way).
I've removed the IAC from the picture.

What else could I possibly do besides physically tension the throttle cable to get my idle right? This is silly lol.

[LoDollar92LX]

sounds like the ecu is in limp mode, causing it to run too rich and stall. you need to clear the code and figure out why limp mode is being activated, bad sensor (coolant temp possibly) or something else as simple as a couple of plugs switched on the engine harness (coolant temp swapped with fan switch)
EDIT: if you have a chipped ecu, then the .bin ROM on the chip is quite possibly corrupt, therefore limp mode. plug the stock accord ecu in if you have a chipped ecu and troubleshoot the car on that ecu to rule out a bad chip burn.

[lucid]

The throttle screw adjustment is probably not the problem, everything else should be checked first. It is meant to be done after the engine has warmed up to temp (and shouldn't need the iac valve anymore), and with the iac connector off. you then start the car and hold idle around 1000rpm, slowly backing off throttle until engine (hopefully) steadies. Adjust to 500-700rpm.

Here is what Honda does.

1) disconnect the electrical connector from the iac valve and, using an ohmmeter, measure the resistance of the iac valve. it should be between 8 and 15 ohms.

2) check for continuity between each terminal of the iac valve and ground. there should be no continuity. if there is, replace the iac valve.

3) turn the ignition key ON (engine not running) and measure voltage between the yellow/black (+) terminal and the black/blue (-) terminal. there should be battery voltage.

4) if the voltage reading is not correct, diagnose the electrical circuit for the iac valve.


The valve you can cover up and don't need is the Fast Idle Valve (FIV), located on the bottom of the throttle body. It will also keep your car from idling properly. To check it is easy, take off the intake tube and cover up the LOWER hole you can see in front of the throttle plate towards the back (inside the throttle body) with your finger. If revs steady, it's bad.
Clogged egr ports can be so bad they cause a misfire. Bad timing, worn ignition parts, and a million other things can cause a bad idle.

Good luck and let us know what works out.

[WilliamW]

Ok so I did some more tests last night and this is what I found. Sorry first some background.

I have the F22B DOHC non V-wack (just a joke) out of the prelude SI. I have the DSM 450cc Injectors and a tuned ECU from d112crzy. Other things I have done probably won't matter but I'll include it just so you can get the whole picture. I have an 8 lb flywheel. ac removed, ps removed, cc removed, CIA, ebay headers. That should sum it all up. Like I said I know I probably don't have to mention that stuff but if some one sees something I don't, that would be pretty cool.

*BACK TO THE WORK*

I took the block plate i made back out and started the car up. With a few pieces from an old wiring harness i cut off the other IAC connector and plugged it into the IAC and stripped off leads and plugged that into the existing sensor connector.

Monitoring the voltage that was going to the IAC with the vacuum leaks sealed off the voltage floated around 3.5 V and 4.3 V never went higher than that. When I applied 12V to the IAC it opened up and the RPM's went to about 1300-1400. This tells me that it's possible for the IAC to control it it's just not, or at least it's not controling it within it's parameters.

For the tests mentioned above.

1)The ohms is at 15
2)There is no continuity between IAC and ground
3)there is 12 volts
4)Voltage reading is correct

[lucid]

I like your way of using an extension connector to monitor the wire without cutting it. Since there is 12v at key on, I would assume the ground wire leads to the ECU, and is used to control the actual valve movement by the ECU adjusting voltages. But I don't know what volts at what rpm / temp / engine load, etc. you should see . You could swap ECUs, or get running voltage readings from another Accord or Prelude.

I'm interested in what is causing this, because mine doesn't idle quite right either. When I push in the clutch, revs go up a little before coming back down, then they can drop down to under 500 rpm once warm. A couple times I've started the engine cold and it will try to idle low. Usually a little tap on the gas will trigger it (the ECU?) to regulate properly. I can also hear some little solenoid (EVAP/EGR) inside the box on the firewall clicking about 15 seconds after I shut the engine off. It is triggered by vacuum loss or loss of electrical power, and I don't know if it's normal or not.

[WilliamW]

I'm probably going to buy some hardware monitoring goodies to see exactly what the ECU is doing. I'll throw this out there, if anyone can do the same as me and monitor their IAC let me know what voltage it fluctuates at. I'm not quite sure what's causing this. I've seen a few people out here with the same problem and from what I'm reading it's all unrelated to what this issue is.


Ah, time to be a MAD SCIENTIST! MWAH HA HA HA HA!