High idle question

[gazzy2000]

hey, i did a search and followed log1call's instructions on setting the TPS, IACV and throttle body.

Engine is idling way high, 2000rpm. (this is my BG5 TT to ST project) the wiring was in a mess but have fixed the major problems. Engine is basically a 97 WRX.

Have tried another IACV, TPS and engine temp sensor. IACV is clean as a whislte.

I dont have the purge solenoid installed but am not getting any codes for that. Wondering if that is something to investigate.

Any thoughts guys?

[log1call]

Hi Gazzy, long time no see.

Air leaks, aircon switch/idle up, neutral switch, alternator control can all affect idle speed.

The purge should be closed at idle, they only open when warm and with a bit of throttle on. You could pinch the hore off though to make sure.

[gazzy2000]

 log1call said:

Hi Gazzy, long time no see.

Air leaks, aircon switch/idle up, neutral switch, alternator control can all affect idle speed.

The purge should be closed at idle, they only open when warm and with a bit of throttle on. You could pinch the hore off though to make sure.

yea gudday mate,

thanks for that, i will check for leaks with butane gas tonight.

Was wondering.. there is a joint connector that has no other earth feed going to it bar the pin on the ECU, i see the last chap spliced this to ground, where-by the wiring diagram for a 97 WRX shows that it dosent go to ground, only the pin on the ECU.

A few sheilded wires, the boost sensor, TPS and temperator sensor all get their earth via this joint/junction connector.. if it was directly earthed wud this casue issues??

cheers

Gary

[log1call]

Hi, wouldn't think so... the shields are all earthed fulltime so if the other wires/sensors are using the sheilds earth as their earth it means they are meant to be earthed full time too.

It could be though that the same reason he had earthed the junction block is a problem now... like a broken circuit board inside the ecu for instance, or the ecu's earth is faulty?

None of those should make it rev high I don't reckon though.

Is it high and steady or fluctuating? Does it vary from cold to hot?

The idle control valve has a water temperature compensating bimetal spring in the bottom of it... From he manual...

Idle Air Control Valve (IAC) operation controls

all idle speeds. Construction includes an air cut

valve, duty control valve, intake air passage and

a coolant passage. These component parts

create a dual control over the IAC. The air cut

valve is influenced by the temperature of coolant

flowing through the IAC. A bimetallic spring is

utilized to act on the aircut valve, opening the

valve when coolant temperature is low increasing

air flow and idle speed. When coolant

temperature is high the bimetallic spring closes

the air cut valve and decreases airflow and idle

speed.

Duty control valve operation is achieved by

utilizing two electrical coils, one to open the valve

and the other to close it. The ECM controls the

ground circuits of the two coils and controls them

with a duty signal, pulsing the ground circuits.

IAC duty ratio can be monitored with the select

monitor. Higher duty ratio will keep the valve

open longer increasing idle speed. Lower duty

ratio provides lower idle speeds. Optimum idle

speed for all engine conditions is part of the ECM

logic and will increase or decrease IAC duty ratio

as necessary to maintain the correct idle speed.

IAC Schematic

Fail-safe results of the IAC can be miss leading.

Failure of the bimetallic spring with the aircut

valve in the more open position will result in no

problem with a cold engine but as the engine

warms the duty ratio of the IAC will be lower than

normal to close the duty control valve more to

maintain proper idle speed. Failure of the

bimetallic spring in the more closed position will

result in higher IAC duty ratio with a cold engine

but will be normal with a warm engine.

Failure of the duty control valve or loss of duty

signal will leave the duty control valve fully open.

With a cold engine the air cut valve is also fully

open. This quantity of air flowing through the

intake air passage would result in an improper

high idle speed. To control this condition the

ECM will turn off injectors to reduce idle speed.

One injector for a warm engine and two injectors

for a cold engine.

The intake air passage can be contaminated with

carbon which reduces the air flow. This condition

would result in a higher than normal IAC duty

ratio. If this condition is suspected clean the IAC

valve following procedures outline in the service

manual.

[gazzy2000]

cool thanks Brett.

I only tried the top electrical part of the IACV, not the whole IACV its self, so i will swap out tonight

My mod on the intake pipe cud be restricting air flow to teh IAC. The the silcone inlet hose is not quite right for my setup so i utilized one of the pipes off it, but it is actual quite alot smaller in diameter.

And from your post:

The intake air passage can be contaminated with

carbon which reduces the air flow. This condition

would result in a higher than normal IAC duty

ratio.

Could be the same result with a smaller diameter hose at one end?? See pics

[log1call]

yeah but the D/C goes high to try and keep the revs up, a blockage is the problem and a low idle is the symptom, the high D/C is the clue.

You have a high idle, which may be too much air flowing through the IAC.

[funkytown]

its not something simple (like MY EXACT same problem this morning) the little nut that acts as the stopper for the throttle cable thingy, wound itself out and wudnt let the butterfly sit closed thus idling high.

see your top photo.. its right in the top right corner just under the thingy the trottle cable attaches too.

something simple to check

[gazzy2000]

 funkytown said:

its not something simple (like MY EXACT same problem this morning) the little nut that acts as the stopper for the throttle cable thingy, wound itself out and wudnt let the butterfly sit closed thus idling high.

see your top photo.. its right in the top right corner just under the thingy the trottle cable attaches too.

something simple to check

nah, i dont think so man.. i checked the mechanics of it and readjusted the butterfly etc last night

thnx

[gazzy2000]

 log1call said:

yeah but the D/C goes high to try and keep the revs up, a blockage is the problem and a low idle is the symptom, the high D/C is the clue.

You have a high idle, which may be too much air flowing through the IAC.

sweet logic there sir LOL

Being that all the shield wires were simply cut at the ECU and NOT wired into the proper joint connector. I think i will start with that. Put it back to the way its menat to be. There cud be noise on the wire.

[gazzy2000]

Well i have rewired all the sheilds into the joint connector ensureing they are ECU earthed, and earthed the ones that go to/from the ECU to the body, they earth else where as well but i also ran them to the earth by the ECU, to ensure a good earth.. i have a earth wire going directly from the batt to the ECU earth mount point.

Started it sheepishly coz i didnt want to wake the kids, it threw CEL 23 AFM this time. I rekon it cud be the signal wire not being sheilded all the way to the AFM, will run a test wire with sheild tomorrow. The IACV CEL only came on after it got to running temp. I didnt let it get to running temp as it is too noisy this time of nite, so i dont know if the high idle is still there once it warms up.

At least everything has mint earths and in the right places to start fresh in the morning.

MISSION!

[gazzy2000]

K

found another power source for the AFM, no AFM code now.

Instantly this morning.. before its warmed up i have code 45 IACV, tried another entire IACV no change.

Still no good, still high idling at 2000rpm.

[gazzy2000]

 CUDDAS said:

Hey Gary,

Im not to sure what the differance between the green ones & yellow ones are, but i see you have a green stickered iacv in the picure & have seen yellow iacv on some other engines?

i have got both types anyway, thanx ;D

[gazzy2000]

K

Tried another AFM, removed std BOV (had the nipple on this one fixed) and fitted a b1tch whistle to elemiate leakage.

No go..

Unlplugged IACV and it idled sweet, so the ECU must be telling the IACV to open, so am gng to trace some more wires...

[log1call]

Wires on the ISC are reversed?

Causing it to move in the wrong direction?

[gazzy2000]

 log1call said:

Wires on the ISC are reversed?

Causing it to move in the wrong direction?

Hmmm yea well that worked Brett (reversing the wirings), it now idles round 1000rpm??

Set teh TPS volts again and adjusted IACV to obtain 800-1000rpm, it intermittantly hunts now too.

But have codes AFM, IACV and TPS.

Maybe it needs a on road reset and a good drive as the plugs maybe a bit fouled up, it is idling but no thaaat nice

[log1call]

Surging can be caused by the butterfly being adjusted incorrectly. The ISC valve needs to be in the centre of it's travel at idle speed or it takes too long to adjust a few revs, so hunts up and down always being a bit too slow to react after the motor revs have changed.. experiment a little bit at a time with the butterfly's screw.

As you say though, clear the codes, go for a good drive using all revs and throttle settings etc to let it relearn.

[gazzy2000]

 log1call said:

Surging can be caused by the butterfly being adjusted incorrectly. The ISC valve needs to be in the centre of it's travel at idle speed or it takes too long to adjust a few revs, so hunts up and down always being a bit too slow to react after the motor revs have changed.. experiment a little bit at a time with the butterfly's screw.

As you say though, clear the codes, go for a good drive using all revs and throttle settings etc to let it relearn.

yea cool, i gots to get a rego and warrant first ;D

Beacuse my BG5 was a 4 plug at teh ECU and is now repinned as a 3 plug WRX (not by me), there is one plug that is bothering me so i think i will completely rewire it and check/trace all wires as i go. I also have a whole v3/4 WRX loom so i can cut the ECU plug(s) off that and they havnt been tampered with.

cheers

[gazzy2000]

replaced one of the ECU plugs, using a ECU plug that HASNT had pins pulled out of it.

And what do ya know... no CELs. its idling like poos but i am guessing the plugs are way fouled from all my start stops.

There was an earth wire i questioned, compaired it to my STI loom and it didnt make sense so bye bye to that wire.

Still idling a little high...but i am guessing the rest of the ECU plugs will have to be replaced too.

ALso i have a shielded 2 core cable wired up from AFM stright to the ECU and the shield earth in its correct location.

[gazzy2000]

YUS! no CELs and purrs like a kitten, just some fine tunning to do with idle etc

Totally rewired new plugs (with un-molestered pins) at the ECU, ran new earths to manifold (nice new thick cable)

Found known earthing fault, will post tomorrow what i did.

Have a lot of work to do to tidy up the wiring etc.... but finally! ;D

[mattapo]

blody good to hear gaz, cant wait to see it running

[gazzy2000]

Hi,

Here is what led me to looking at earthing issues, it is a link publication on one of their manuals for 4 Plug ECUs, stating known earth problems.

So here is the earthing system for a 3 plug WRX set up, which is what the car is being converted to (remembering mine was a 4 plug)

I cut off the factory earths at B136 12, B136 18 and B137 24 then soldered the wires from the aforementioned pins/plugs together with a thick earth cable that runs straight to the manifold.

I then did the same for B137 14 & B137 25 (have a look at the above pic for pin confirmation).

The different colour wires in the below pic is just so you can see where the cross over each other.

Where the old earth wires were cut from the loom i just taped them up.

Under the bonnet i ran the same sized cable from the where the new ECU earths attach on the manifold to the passenger strut tower then to the batt -ve.

Also, for a better connection/earth solder the eyelit terminals on to the earth cables (dont crimp them) then clean the bolt and manifold where they all mount

For the AFM wiring i ran new twin core, twin shielded cable which has to be 3 times better than the factory cabling as the wires are thicker, its double shielded and its not run along side other wires in a loom.

[log1call]

Nice work Gazzy!