Engine hesitates at low speed/RPM

[Paddy Honda]

Throttle body is clean, its not the ICM and it doesnt misfire. It idles smooth, its the the kangaroo hopping when its hot and I'm trying to keep the revs steady at around 1700rpm to 2500rpm.

As a side question, I'm removing my IACV and I dont want to throw an engine code. Any ideas how I can fool the ECU? Is it checking for a resistance to know that its still there?

[dc2r-0636]

How do you know the ICM is fine??

When i had this issue it would run fine when cold. Then when it warmed up it started spluttering/misfiring when cruising below 3k rpm in any gear.

Its not the injectors in the case because it would happen all the time not just wen its hot.

[Paddy Honda]

Fair point, I'm just assuming that the ICM is fine and we all know what happens when we assume.
I actually have a new dizzy on order so hopefully it'll be here in the next day or 2.

I removed the IACV last night and put a blanking plate over it and now the idle is down to about 950rpm which is much better than the 1500rpm it was running at.

I dont have an FITV on my TB, just a port where the coolant passes through the TB and then goes to the IACV. I want to remove these coolant lines and take the IACV out completly (its cable ties to the bulkhead at the moment).
The cars a rally car and not road registered so its hard to get it out for a spin. I did get it up to running temp last night and just went up and down in front of the house to see if the issue is still there after I removed the IACV and it seemed fine but I remember that its only after driving it for a while, not just up to temp that the issue comes in.

[Paddy Honda]

I found this write up on another forum. Some good information in it. Hopefully it hasnt been posted before:

How the idle speed is controlled
The idle speed is controlled by three methods:

The cold idle value, which is located under the throttle plate. Late model engines may not have the cold idle valve. The valve consists of a air channel bypassing the throttle plate which is blocked once coolant heats up a wax element. When the engine is cold the cold idle valve will allow a lot of air to bypass the throttle plate, and the idle will be around 2000 rpm. As the coolant warms up the cold idle valve will slowly close, bringing the idle speed down.
The idle air control valve (IAC or EACV), which is located on the back of the intake manifold. The IAC valve is a solenoid which is controlled by the ECU using pulse width modulation. Thus the ECU can control how far the solenoid is open and how much air bypasses the throttle plate. There are limits, both upper and lower, to the amount of air which passes through the valve because the solenoid will only work from 20% to 80% duty cycle.
The throttle air bypass screw, which is located in the top of the throttle body. Unscrewing this will allow more air to bypass the throttle plate, and so will increase the idle speed. The purpose of the bypass screw is to adjust the amount of air going pass the throttle plate so that the IAC valve duty cycle is within the limits of what the ECU can control. The manual tells you how to adjust this screw by unplugging the IAC valve.
TPS adjustment

The TPS tells the ECU what position the throttle is in. The TPS should read 0.45V when the throttle is released. It is critical that the TPS is adjusted correctly so that the ECU knows when the throttle is released, which tells the ECU that the engine is either idling, or the throttle is closed under load and the injectors should be switch off the save fuel (fuel over-run cutoff).

If the TPS is set negative (below 0.45V at idle) when you open the throttle slightly the ECU will think the throttle is not open, apply the fuel over-run routines and cut fuel at 1400 or 1800 rpm. This will often cause the revs to cycle between about 800 and 1800 rpm. Also the car will be jerky when driving around at low speed.

If the TPS is set positive (over 0.45V) then the fuel over-run routines won't work, and also the ECU will not run the correct idle routines to keep the idle steady. It's better to have the TPS adjusted slightly negative, but setting it to 0% if fairly easy with datalogging. Otherwise aim for 0.45V.

Effect of mixture and timing

Normally at idle the ECU will run in closed loop, so the mixture will vary around 14.7:1 Running in open loop and enriching the mixture to about 14:1 increases the idle speed.

The stock setting is slightly retarded at idle. Adding 3-4 degrees ignition advance in the idle portion of the ignition tables increases the idle speed.

Idle problems and oscillation

The ECU has a 'target idle speed', which varies with coolant temperature and electrical load. When fully warm the target idle speed is 700 or 750 rpm. If the engine speed is different from the target idle the ECU will alter the duty cycle of the IAC valve to compensate. A combination of a duty cycle lookup table, the current duty cycle and the difference in idle speed is used to calculated the duty cycle for the IAC valve.

This is a closed feedback loop, and is dependent on the characteristics of the engine matching what the ECU has been programmed to expect. If any of the components in the feedback loop, or a combination of components are different from what the ECU expects, then the feedback loop fails apart and the idle will often oscillate. Don't confuse this with the oscillation which can happen if the TPS is out of adjustment and the over-run cutoff is operating. The idle oscillation is a good example of a lorenz attractor in non linear dynamics if anyone is interested is chaos.

For an example consider that the engine is idling at 750 rpm by using a duty cycle of 25% for the IAC valve. The engine speed drops to 725 rpm, the ECU calculates the difference of 25 rpm and calculates a new duty cycle. The tables in the ECU tell it that when the IAC is at 25% duty cycle and the idle is 25 rpm low, use 30% as the new duty cycle. This valve has been set by Honda as the correct duty cycle for the stock engine, and will return the idle speed to 750 rpm for a standard engine. If the engine has been modified it might be possible that the IAC duty cycle needs to be 50% in order to increase the idle speed again. Because the IAC duty cycle is too low, the idle speed drops, and eventually the ECU will give the engine a shot of fuel and open the IAC right up so that the engine does not stall. This will raise the engine speed to 1000 rpm or so, and the cycle continues.

The solution is to alter the behaviour of the idle speed components so the system is stable again. Usually adjusting the TPS, idle bypass valve, mixture and ignition will cure an unstable idle.

[Paddy Honda]

Ok, so the latest update is as follows:

I removed the IACV (but left it connected to the ecu) and plated off the bypass and started the engine, it now idles at about 900rpm which is good. Took it for a spin and the issue is gone. At low rpm, when I back off the throttle, it doesnt hesitate anymore.
So I tried a few things.

I cleaned the iACV and checked its opereation by putting battery voltage on it and it seems to work fine. I put the IACV back on and the revs were back at 1500rpm and the issue was back.
With the engine running, I removed the plug from the IACV and the revs dropped to 900rpm, so this tells me that its not a vacuum leak, something is making the ECU tell the IACV to open an amount.
So with the IACV in place but the plug removed and revs at 900rpm, I drove (MIL on), and the issue is back. I'm stumped.

It seems to be ECU related alright. The ECU is telling the IACV to open to compensate for something (a load) that isnt there and thats making the revs high but it seems that the ECU isnt expecting the revs to be that high. I have no idea.
So for now, to get over the problem, I have put a plate over the bypass holes and put the IACV on over that. That way, the ECU is happy to still have the IACV connected but the IACV cant influance the revs anymore and the car runs good???

Anyone got any idea?? Do I need to fool the ECU about A/C on, Power Steerig load etc as I dont have any of these signals anymore??

Thanks

[Fanaticz]

I actually have sort of the same issue with my car

This is what I've done so far:

- Oil change
- Oil filter
- Coolant
- Spark plugs
- New Battery
- Reset ECU
- Cleaned Throttle body
- Cleaned IACV

The car cranks but won't turn over!!!

I've spoken to a mechanic at Toda Performance and done some extensive research (google ftw), from what I can tell I probably need upgraded fuel injectors as the stock ITR ones (240cc I believe) aren't as good for whats been done to my car.

I believe my car sits around the stage 2 area (may be close to stage 3) of modification and I've read to expect a high/rough idle, on that note higher stages of modification will require upgraded parts (no shit sherlock :P)

Regards
- John

p.s I bought my itr already highly modified, but I don't regret it as I would never have put as much effort into researching as I have done so far

[nugget]

I actually have sort of the same issue with my car

This is what I've done so far:

- Oil change
- Oil filter
- Coolant
- Spark plugs
- New Battery
- Reset ECU
- Cleaned Throttle body
- Cleaned IACV

The car cranks but won't turn over!!!

I've spoken to a mechanic at Toda Performance and done some extensive research (google ftw), from what I can tell I probably need upgraded fuel injectors as the stock ITR ones (240cc I believe) aren't as good for whats been done to my car.

I believe my car sits around the stage 2 area (may be close to stage 3) of modification and I've read to expect a high/rough idle, on that note higher stages of modification will require upgraded parts (no shit sherlock :P)

Regards
- John

p.s I bought my itr already highly modified, but I don't regret it as I would never have put as much effort into researching as I have done so far

if the car cranks but wont turn over, most likely ICM or coil.

how modified is your car? whats been done? what ECU?
i think stock itr injectors are capable of 130 wheel kw.

[Fanaticz]

if the car cranks but wont turn over, most likely ICM or coil.

how modified is your car? whats been done? what ECU?
i think stock itr injectors are capable of 130 wheel kw.

Last dyno run in early 2009 was 132.5 atw, I don't have the specific list of aftermarket parts(at work atm can't access my hotmail) but here is a summary engine wise:

Toda spec b cams (installed by Toda Performance)
Fujitsubo exhaust
Apexi GT Manifold
Greddy oil cooler
Ogura racing clutch
Mugen CAI
AEM racing ECU (Toda mechanic said this was pretty meh)
4.9 Final Drive
Also has a oil catch can (possible home job)

A whole new dizzy and Timing belt was actually put in around the time I bought it. Although there is a bit of a squeal around where the alternator is.

P.s sorry if it seems like I'm stealing this thread XD

[tiksie]

Had similar issue with my JDM B16:
http://www.ozhonda.com/forum/showthr...HAS-BEEN-FIXED!!!!!

Ended up being the timing.

Do you have the jap del sol b16 by any chance ?

[Fanaticz]

just an update,

I put in some fuel injector cleaning fluid and my car has been running sweet so far, so next stop is having them cleaned in a ultrasonic bath

The squealing from the drive belts still persists but I'll be having those changed aswell as the tensioner

[nugget]

just an update,

I put in some fuel injector cleaning fluid and my car has been running sweet so far, so next stop is having them cleaned in a ultrasonic bath

The squealing from the drive belts still persists but I'll be having those changed aswell as the tensioner

hmmmm.... look back at reply #2..... lol

so you going to change the belts? or just re tension?

[dc2r-0636]

Hmm weird, if injectors were the problem the problem would always be there, not just when the car has warmed up. Injectors stay the same temp