R33 Idles At 1200rpm Going Insane

[r33gts4turbo]

Ok after hours of research and even more time spent under the bonnet im calling for help

My cars idle is at around 1200-1300rpm once warmed up(was like it since i bought the car 3 months ago) r33 RB25DET motor

Mods:

exhaust

filter

fmic

walbro pump and sard press reg

stock bov

Now the acc valve screw is wound almost all the way in(i cleaned the acc valve by the way).The throttle body "stop" screw is untouched .The tps has been adjusted to .5v for closed throttle.There are no air leaks so to speak.

The cold start hose was blocked(once warmed up)to see if air is passing through the bi metallic thing(or is it the other way around??) and into the manifold but seems ok.

Now,if i crimp the inlet hose which runs to the acc valve the car will stall.... so thats where the air is coming from.If i disconnect the brown plug (on the solonoid) on the acc valve the car stalls.Now if i adjust the acc idle screw so that it idles at 750rpm ..i then reconnect the brown plug and bang up goes the idleto 1200-1300rpms.For some reason the brown plug

on the acc valve raises the rpm by around 500-600rpms (and even more when the aircon is switched on).Is this normal?

any ideas or help would be much appreciated

thanks

[RB30-POWER]

spring missing from aac valve, i.e. when removed is the valve able to be pressed in and spring back out on it own?

ecu could be f**ked causing 100% duty cycle meaning its fully open all the time or a short circuit to earth will do the same, so check the loom isn't shorted to earth on the ecu switched side/pulsed wire side.

if you have a multimeter that can measure duty cycle put it across the wires on the valve and see.

Edited February 23, 2008 by RB30-POWER

[r33gts4turbo]

hi thankyou for replying.

yes the spring was in the acc valve and moving freely/nicely and seating correctly after i cleaned it.

The ecu is a factory one but has a mines racing sticker on it..

So i should put a multimeter across the wires on the acc valve brown plug at idle?

thankyou

[RB30-POWER]

only if it has duty cycle % measurement.

you can try and measure voltage, but the multimeter may not be fast enough.

if you measured voltage and it was 100% on you would measure full battery voltage, if you measured say 6-8v you would know the valve is being driven at less then 100% as it should be, it should be driven at almost 0% if the idle is higher then what its target value is. (very low voltage measured)

it will also target high idle if it thinks the coolant temperature is low as well, maybe there is no fault but it thinks the cars is cold and trying to target 1200rpm, does it uses much fuel blow smoke or runs fine? (check with consult would be ideal if you have access to it)

coolant temp sensor specs can also be found on this site and can be checked.

because from what you are describing, its not a vac leak, its whenever you hook up the aac valve its being driven 100% fully open, but why is what you need to find out.

[r33gts4turbo]

i have just warmed up the car and measured the voltage across the acc valve solonoid plug (brown plug) and it gives a reading of 15v at idle.

The car is very heavy on fuel and the car smells rich even at idle.Even when the car is idling at 1200rpms i hear it (pop sound)but not loud but like a old carby car where it has been fully warmed up but the choke is still on if you know what i mean.

So if the temp sensor is giving an incorrect reading .. this can cause the car to idle high/run rich?

thankyou for your help much appreciated

[RB30-POWER]

the coolant temp sensor, acts as a choke so to speak, when the car is cold it needs more fuel and a higher idle to not stall.

if you give the ecu a false signal (like a faulty temp sensor), telling the ecu its cold it will run rich and have a high idle even if its actually warm.

the coolant temp sensor is the two pin connector alongside the single wire sensor (for dash guage) near the top radiator hose on the engine inlet manifold.

can you measure the voltage at the battery whilst the car is running at idle and also rev engine to 2000rpm and check the voltage.

15v is rather high, but it might just be the multimeter is low quality and not calibrated properly, if you rev it up and it doesn't go over 15V like at idle, we will assume its just a bad reading multimeter, if the voltage goes well over 15V it might have a faulty regulator in the alternator causing overcharging.

[GeeTR]

^^ RB30_POWER, they're some fantastically well written posts!!!

Edited February 23, 2008 by GeeTR

[r33gts4turbo]

ok

well today i got myself another multimeter and checked the charging voltage and its just over 13v at the battery and doesnt change when the car is revved.

Now i measured the coolant temp sensor and it reads 22ohms when cold and around 3ohms when fully warmed up.

I also tried starting the car with the coolant temp sensor unplugged (as an experiment)and it struggled to idle but once i plugged it back it it idled up to around 1300-1400 rpms when cold and then drops back to 1200rpms once the cars fully warmed up.

i also checked the ignition timing too which was ok.

So im really at a loss as to why the car is idling so high... i guess my next step is to replace the ecu because i cannot think of anything else it could be.

[mattymagoo22]

is there slack on your accelerator cable? Not being smart ass but KISS method is important.

[blind_elk]

The TPS is a 2-part component - a throttle position SWITCH and a throttle position SENSOR. The SWITCH part of the TPS needs 0 ohms across pins 1 & 2 (or 2 & 3) at throttle closed to tell the ECU that the throttle is closed.

Does the engine tend to hold revs on (up) gear changes? If it does, the the TPS(witch) is likely out of adjustment; the ECU should shut down the injectors when the throttle snaps shut during gear changes.

[r33gts4turbo]

Hi,

yes there is a little bit of slack on the cable and the throttle body rests on the screw stop.

I do believe its an electrical sensor telling the computer something it shouldnt causing it to idle up (via the solonoid on the acc valve)

Blind elk.... i will have a look at that this afternoon as that is something i havent checked thankyou.Can the tps be adjusted for the throttle closed position?I remember adjusting the tps for 0.5v at idle using one of the 2 plugs attached to the tps.So do i measure the other plug on the tps for the throttle closed measurement?

oh ,the revs do come down between gears but not past 1200rpms

thankyou

Edited February 25, 2008 by r33gts4turbo

[Tweek]

high idle is usually air leak after the throttle body. check the inlet manifold gaskits. had same problem, cost me a fortune coz my plenum was warped