I got a 00 Integra ls with a bad idle going up and down...at a cold start it idles at 1500 and slowly goes up at 2000 and then starts to go up and down....I replaced the thermostat cuz it was stuck open and didn't let the engine get up to normal temperature so after I did that it only did it when it was cold and as soon as it got warm it idle fine right below 1000 rpm but that only lasted for 2 days and started doing it again...when it's warm at a stop it idles at 1500 with a hunting idle going up and down really fast and drives ruff with low performance...i got a code p0505 idle air control system so I checked the iacv and it was clean...tested it by connecting the power and ground wire to the battery and it seems to be clicking fine the coils are opening and closing when touching ground .checked the tps with my volt meter and I'm get proper voltage at open and close... Could it be my ecu cuz I think it was an automatic converted to a 5 speed and might have the old ecu and now it redline at 5000 rpm ...just bought the car and it's driving me crazy please help I don't want to buy parts and not be the problem

 

Well check the ecu. What's the sticker on the side say?

 

I hope the OP doesn't mind me jumping but I have an idle problem too.

Sometimes I turn the car on and it idles incredibly low, like 2-300rpms. Occasionally it shuts off. Or other times it idles at like 1500rpms then as its getting warmer, it goes down below 1000rpms.
I've cleaned the IACV before, the problem still persists, I just changed the spark plugs (needed to anyway), still happens. Any other troubleshooting ideas?

By the way, it's an original motor (Acura Integra, b18b1)

 

P75 *** I balibel the *** shows it's an automatic ecu...and something with lower numbers like A05 is a manual ecu

 

Yea, so the Automatic Integra's and Manuals from 1996 and up control the idle differently so that's why your getting issues. Assuming everything else is still OBD2 (wire harness, plugs, etc.) then you need to get an OBD2 MANUAL ecu. I would be weary of a lot of stuff from here on out though because anyone who's even half decent at car stuff would know that you have to put in a manual ecu when you do a manual swap.

 

Alright I ordered one and should be getting it by Wednesday next week thanks man

 

Also, do you know about the key immobilzer system that Honda started using in 2000? That may give you some issues assuming that it's currently working and functional with the Auto ECU right now

 

Yeah I have to take it to a Honda dealership when I get the other ecu right and get it reprogrammed..how much you think that would cost?..or is there a way to do it myself

 

Absolutely no way to do it yourself unfortunately. And your new ECU has to be 2000-2001. 1996-1999 OBD2 ecus don't do the immobilizer thing. So assuming your new manual ECU is from 2000-2001, the dealership won't be programming the ECU, but they'll be programming a new key to work with that ECU. It'll run around $100 I believe for a new and programmed chip key. Anyway, for them to even do this you'll have to have some proof if the VIN # for the car the manual ECU came out of and why it's not in that car anymore. This is just for security reasons so you can't just make keys to other people's cars

 

Ok yeah I ordered a 00-01ecu from ebay but looking at the engine I'm just now realizing it say 99 under the valve cover on the block...I heard that's the year of the motor..should still work right?

 

The casting date on the head can be a year earlier than the car's release date. They have to make them ahead of time. Check the car's VIN number for it's year. Also, do you have the key light on the gauge cluster? If so than that also means it's '00-'01. Assuming the car's immobilizer system is still in tact and hasn't been bypassed, then you'll need to look into getting a key made that works with your new ECU. Or maybe the ebay listing says it comes with a key?

 

Yeah the key light dose come on...I'm just going to take it to get new keys and programed...just hoping it fixes my idle problem ....thanks a lot for all the info much appreciated

 

Sounds good man, glad to help. I'd talk with the dealership first or even do some research about the process of getting new programmed keys made. Because while they can do it for any ecu, there's the security risk of allowing people to get immobilizer keys easily. Also, Does your throttle body have the fast idle thermo valve underneath it?

 

Yeah I called them and said they can do it told them my situation and that I'm ordering one from eBay ...and no mine don't have one ..I checked for leaks.the iacv cleaned and checked it if it clicks and opens and closes when connecting it to battery.....checked the tp sensor voltage open and closed....the only thing I'm left with is the ecu or maybe the timing can be off ...oh and I bleed out the coolant for air and I think I did it right read that all you need to do is run it for a while with the cap off untill you see no more bubbles come up ..might do it again just to make sure

 

starting in '96, manual tran Hondas stopped using the fast idle thermo valve while the automatics still used them. So it's good that you don't have it or else you'd have to bypass it. BUT, you still need to check if you have the correct IACV. There're two different ones. One for manuals that don't have the FITV and one with the automatics and OBD1 cars with the FITV.
Here's a picture of the IACV for manuals (what you want to have)

And here's a picture of the one for automatics

Notice the smaller opening on the one port for the auto IACV. You want to make sure you have the one for manuals that has the fully open port. Again even if you have the correct one, it won't matter until you get that new ecu on there and running. But just a heads up that there are two different types

 

Yeah I got the right one awesome

 

Wait so if I get the automatic iacv it should fix it then .it'll cost me a lot cheaper cuz I payed 100 for an ecu.and the honda dealership is going to charge me 202 plus tax when I can send the ecu back and order a used iacv for around 40 bucks and can still hold the other one untill I can afford to do all the reprogram and new keys don't you think......it should work right

 

Umm possibly. You would still need to get the fast idle thermo valve and the throttle body that goes along with it because the auto iacv works together with the fitv. But if you do that than maybe. The only thing I'd be concerned about are any other issues for an automatic ecu paired with an engine that has a manual tran. I'm not too familiar with it as I've never had an auto but I know the ECU works in conjunction with the TCU (transmission control unit) in deciding how much fuel to run given the rpm based off of engine load, what gear the auto tran is in, yadda yadda yadda. I'm be willing to bet the major cause of your performance loss issue is just because you're running an automatic ecu. Anyway, do some research into using an auto ecu with a manual transmission and if you feel comfortable doing it then I actually have the right IACV, FITV, and throttle body for you. I'd do $80 plus shipping for all three.

 

You know what your right cuz I also got codes for a problem in torque converter clutch solenoid valve B circuit and a open in transmission range switch circuit ....I'm just going to get the manual ecu to make sure it's how it should be....might not need to get a hot smog if I can just fix it with the ecu and take it to get state ref for the manual conversion...do you have an idea how much or how that works

 

I have no idea what a hot smog is. But I'm sure if you get that idle down to 750+- 50rpm and all of your vacuum lines are set up like stock oem than you shouldn't have any problem passing emissions.

 

Idle "hunting" is commonly caused by a bad MAP sensor. Sometimes the vacuum port is clogged, but it's usually a bad sensor. Typically there will be no code indicating the MAP sensor, just a code for the poor IAC which is obviously working hard, since the idle increases and decreases.

 

Check if your iacv is working... turn your car on and see if you can keep it running and unplug the harness and see if that changes anything if not your iacv might not even be working... another way to check it is to connect power to the blue/yellow wire to your battery and the black n blue wire to ground....by touching the ground wire to ground on and off it should make a clicking noise opening and closing the valve . If it's not clicking it's no good anymore ...or your nap sensor is bad

 

If your idle goes up and down (idle hunting), then you know the IAC valve is working and the computer is in control of it. The fact that the idle is too high points to a bad input, typically it's the MAP sensor. Look at the fuel trim data, it's probably -10 Short Term and -10 Long Term, maybe more. The MAP data will look low, like 7 or 8 in. hg. It fools the ECU into thinking there is a load that's not there, so it can't get the IAC to stabilize, sets a code for the IAC, instead of the MAP. The key to the diag is the idle hunting, it should immediately tell you there is a problem with an input that the ECU cannot compensate for.

 

Thank you for that, I'll check that using both ideas when I get the time and let you know how that goes.