RB25DE+T PFC idle

[WYTSKY]

RB25DE+T PFC idle

Hey guys,

Had this minor annoyance for a very long time, from memory probably since the powerfc was installed and tuned 6+ years ago. Maybe because I'm getting older it's starting to annoying me more.

I turn the car on in the morning and idle is high, 1500-1700rpm, but stable. On the hand controller it all looks pretty stable, not sure if idle this high when cold is normal with other powerfc's but so far it doesn't annoy me.

As I'm driving around and idling at lights while the car is still warming it's still sitting at 1500rpm, on the hand controller once the water temp gets to about 59-62 degrees it starts hunting, from 1500 rpm down to 900rpm and back and forth every 1-2 seconds and will continue like this until the water temp gets to about 72+ degrees then idle is perfect, 850-900rpm. The only way to control it during this time is let off the clutch a little bit until it bites and slowly lower the revs, then I slowly press my foot down on the clutch again. If I put my foot down too quick on the clutch or roll forward a little the hunting starts again.

Only happens when the car has been sitting for a long time, eg overnight or all day and then come back from work and turn it on. If the car gets to operating temp and then I turn it off for 1-3 hours and the engine is still pretty warm no issue, idle is perfect.

Now before I start playing with the TPS voltages and mucking around pulling apart things I'm wondering if this is just something in my maps in the low load/idle section that needs adjusting as it only happens for ~10 degrees so I would have guessed the voltages on the TPS are fine? Car has been tuned a number of times many years ago by a very reputable tuner.

It happened as soon as I swapped the standard ECU to the powerfc and it has been like this ever since, even with adding in cam gears and a z32 AFM. I have used contact cleaner to clean the AFM and I've cleaned the AAC with throttle body cleaner and ear buds in every little knook but no avail.

Any suggestions?

I've found this post from long ago which seems almost identical so I'll give turning off O/2 feedback a go (not sure if it's enabled currently or not) but wanted to see if others had the same issue?

 

Thanks.

 

 

 

[GTSBoy]

May well be the AAC - the water heat heated idle valve starting to close at that temperature.  That's not the problem, but the trigger for the problem.  I would then guess that the IACV is dirty enough to not be responsive to the ECU's commands and so the ECU loses control of the idle.  When it drops too far the ECU throws the valve open more and it suddenly is too much valve and the idle rises too far and it throws it shut.  The ECU might also be pulling and re-adding timing to gain control.  (I don't know if PFCs retain that ability).  Rinse and repeat until the car is warm enough that it settles down.

So it may just be that you need to dismantle and clean the IACV.

Edited November 15, 2016 by GTSBoy

[Ad's]

Mine idled like crap when I changed to larger cams and my tuner tried a few different things and couldn't get it to idle right, 650-1200rpm. I tried different clean IACV's, disconnected the plug and tried resetting it, tps voltage and nothing really helped.

I played around with the idle settings in the hand controller and it as a slight hunt for about 20 seconds and then idles at 800rpm, I have a lightened flywheel witch I do believe was causing the excessive hunting with the old idle values but its mint now. Ill be going back to a standard flywheel soon, not because of the idle hunt but more because its a pain in the arse to drive but I'm interested if the start up hunt still follows or not.

[WYTSKY]

Thanks guys,

I've cleaned the IACV multiple times, let the throttle body cleaner really get in there and then scrubbed every part of it with cotton ear buds until the buds came out clean ( took like half a pack) let it dry, installed it and no difference. If I'm honest, the only thing i noticed was the hunting was slightly more aggressive then when it was dirty but that was about it.

Perhaps buying a second hand one to test with might be needed.

 

 

[WYTSKY]

So I checked and the O2 sensor was enabled, disabled it, made a slight difference, the hunting was less aggressive, as in it didn't rev up and down as quick but it was still doing the same thing so I put it back for now because it didn't stop the issue.

Then I used the sensor check on the hand controller and found the TPS idle was a little low for idle. 0.35v closed, 4.18 WOT.

I've now adjusted it to be 0.44v closed (every time I got .45 then tightened it moved), and 4.24v WOT.

The car is warm so wont be able to check till the morning but when I did turn it on the idle *seems* smoother already.

Any issues foreseen with WOT 0.06V+ more then before affecting my tune etc?

 

[Ad's]

My tps voltage was about the same as yours, I set it as it should be and I think it may have played apart in helping it. Adjusting the tps wont affect the tune, you are only telling the computer what position the throttle plate is at.

[666DAN]

Leaky charcoal/carbon canister?

[WYTSKY]

Thanks Ads, thought as much but just want to be sure. 

Dan, I'll check it to rule out. 

Still haven't had a chance to drive it since adjusting the tps. Will report back once I have. 

[WYTSKY]

Ok so I took it for a decent drive today. Definitely a big improvement.

It's hunting less aggressively and the revs aren't dropping as much - instead of dropping from 1500rpm - 900rpm and back and forth it's now only dropping to 1200rpm and back to 1500rpm slower.

So what's happening now:

10deg-59deg high idle (1500RPM) stable idle, 59deg-71deg hunting still, but no where near as bad and only 1200rpm-1500rpm, 71deg+ normal stable idle at 900-950rpm.

So the questions I have:

- Is there a way to adjust that 1500rpm cold idle to sit at 1200rpm when cold to fix the last problem? Where to start - the Idle screw in the IAC? But that would adjust my idle overall. 

My idle settings in power fc are fine as far as I know :

rev limiter 7200

f/c A/C 1100

f/c A/C 1000

idle A/C 900

idle A/C 900

- Should I try to adjust the TPS above 0.45v for idle to bring it up to 1500rpm when idling cold? or safer to leave it where it's at now?

-Any other thoughts? I am already much happier with the result and reckon I can live with it now but would be good to fix it overall if it's just a matter of fiddling.

 

Thanks.

 

[Dose Pipe Sutututu]

raise the fuel cut 

[Ad's]

Good to hear you are making progress. I'd be playing around with the iacv once it's warm, search for the thread and I believe that should sort it out.
If I get a chance today I'll have a look at my idle figures and compare, but every car is different.

[89CAL]

Was the idle learn procedure done correctly when the power fc was installed?

[WYTSKY]

Johnny, thanks, will have a fiddle, I have wondered if that would help.

Ad's. appreciate if you could compare values, I know each car will be different but to get an idea if mine is in the ballpark like I did with the TPS would be good. Would it be best to adjust IACV when car is in the hunting rev range or wait until it's at full operating temp?

89Cal, I'm not sure, been so long since it was done, I don't have a datalogit cable to backup the tune/reload otherwise I would do a new idle learn.

[Ad's]

I can have a look and let you know, I have larger cams in mine so not entirely sure if mine will be any help if it affects it the idle at all.

From memory (might not be correct) you need to let the car warm up to normal temp, disconnect the tps plug and wind the idle screw until it idles at 850-900rpm then connect it back up.

If I had a datalogit I wouldn't mind doing my idle re learn again and hoping it fixes my minor hunting on start up, but considering mine is running e85 I let it warm up before moving anyways.

[Dose Pipe Sutututu]

do you have access to a wideband?

see what's going on with the o2 during o2 feedback enabled and disabled. 

[WYTSKY]

Hey guys, final update.

Decided to take the car into work this morning (cold morning, stop start traffic for over an hour) used to be the worst scenario to make it hunt and rev a lot.

All is perfect. Was great drive in, just purring while stationary the whole way so I'd say it's fixed!

I did end up adjusting the fuel cut a bit which is what fixed the last bit of revs issue.

So now my settings for Idle on the power fc are:

rev limiter 7200

(aircon Off) f/c A/C 1110

(aircon ON) f/c A/C 1100

(Off) idle A/C 900

(On) idle A/C 900

I previously had the 1100 and 1000 I said earlier around the wrong way.

So now what happens is high idle from 10 deg->68/69 deg (1500-1700rpm, but smooth), once past 69/70 idles at 900-950rpm. that's it, perfect and smooth.

 

So as a summary the steps I did to solve the problem:

1. Adjusted the TPS to read 0.45v on closed

2. Raised the fuel cut with no air con from 1000 to 1110

 

Other things that may have helped:

1. Cleaning the IACV with Carby cleaner a couple weeks ago

2. Turning the O2 sensor On/Off to see if the O2 sensor was dead, my sensor is now ON and appears to be fine.

 

Thanks for all the great help as always.