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high idle issues - what else could affect it if I've altered the warm-up enrichment

anthony mcgrath

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hi all

I've been having a high idle issue on my R33 skyline GTST since the ecu went in and I cant seem to find out what the problem is.

I fitted a nismo thermostat and an oil cooler about 4-6 months ago.

the oil cooler came off just before xmas because the oil just wouldn't warm up and the oil pressure was mental high all the time!  ..and this week the nismo thermostat came off (whilst having a clutch change) and an oem thermostat (new) put back in.

So I'm quite happier now - oil temps climb to a more respectable 70degrees and ECT seems to climb to about 62 as it goes through warm up in the garage.  With a run out and return it climbs a bit higher and oil pressure is more sensible.

I'm pretty much at the point where the ol' gal is ready to be mapped :D

Anyhow with those things being a bit more sensible I thought I'd have a go at editing the warm up enrichment.  I ran through it last night editing the value on the 0% TP as it warmed up.  At 70degrees I've got it so the warm up enrichment is pretty much decayed out completely.  I attached a screenshot to show what I mean.

My problem is that the car STILL doesn't seem to be dropping in terms of RPM - its still idling quite high.  If I take it out for a drive the RPM is lower at 40mph than the idle at traffic lights!  If I pull up at lights the idle will literally climb to about 1500-1600rpm.

I'm just a bit lost as to what I can adjust now to bring it down.  I've checked the idle valve and thats screwed in quite far lowering the idle and there aren't any air leaks either as the idle isn't hunting or anything.

I've attached shots of my Warm Up Enrichment and IGN table for reference.

anyone got any ideas

thanks :)



ps sorry for long post - just trying to cover the angles and full picture of where the car is at.



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extra air leaks can be tricky to find, grab a bit of air line and use as a stethoscope to hunt *everywhere* around all fittings and joints to try and track down extra air suction holes.

 *-*-*-*  BE CAREFUL you DON'T put tube in your ear, if you find a suction point, and its in your ear, you could *DAMAGE* your hearing !!!!

If nothing is found, try removing the throttle body and look through it with a bright light on the other side, to check for sealing around the butterfly, or pull down the 'idle' screw to check that its actually closing down far enough, and not jamming up on some 'gunk'

as last resort (with engine stopped) remove a air line from the intake tract (after throttle butterfly) and attach a air gun to that line to inject some air in to the intake chamber, placing your hand over the throttle body then releasing the air from the gun and see how long it takes to 'deflate'... I wouldn't really recommend this way, but it worked with me and the 2x M6 holes that were left open during a temp sensor modification :P  and maybe your air line routing destinations may not be too happy being pressurised (not an issue for my set-up)

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hi Rod thanks for your reply!

Yep a friend suggested the idle screw but I cleaned that out before I fitted it onto my plenum.  I recently removed the adjuster screw and I put some ptfe tape around it to help create a better seal as the little rubber grommet thats supposed to do that job was jaffed and I cant get another one.  The adjuster screw on the idle valve does adjust the rpm but i've screwed it in quite far now and it isn't really gonna go much further and the rpm is still high.

The throttle body all seems okay but It wouldn't hurt to take it off and check.  Usually if there's any air leaks the car tends to hunt but its not doing that really - its just a permanently high idle.

HOWEVER! a friend on another forum pointed me to the following in G4


when I look at that I see from 20 to 60 degrees ECT there is as much as 5 degrees extra of ign timing.  I'm almost certain its this causing the issue as when I tried editing the ign in the table (before I knew about the trim menu!) the rpm did sound like it was going down but the issue was that the rpm was going lower than what I would have liked even by 1 degree. 

With the trim table I should be able to zero that lot out (leaving the values alone after 100ECT which retard ign I imagine as a safety protocol).

I'm gonna try it tonight and see what I get.  I imagine it might be a conglomeration of issues but looking at that table I'd say the extra 3-5 degrees ign isn't helping really.

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well just to append to this thread... I found out that my high idle was actually down to my Q45 throttle body.  It has a throttle jacker device that works kinda like a thermostat.. a little plunger pushes open the throttle body slightly whilst cold.  Water is fed through the throttle body and as it heats up a waxy substance melts and allows the plunger to push inward effectively relieving pressure off the throttle linkage (that bit that the wire is connected to) and lowers the idle.  I didn't know about this but its easy enough to remove so I took it out and bingo!  The idle dropped right down. 

The water being fed through the throttle body actually isn't needed which is why I didn't know about it as the gtst has a cold start valve.

I then disconnected the ISC solenoid control in aux_outputs_fuel and adjusted my idle valve mechanically using the idle valve adjuster screw under the hood!

After that I re-enabled ISC on the G4 and was able to adjust the idle.


I still have some issues in that with alot of load (headlights, music, heater) and use of the power steering as I come to traffic lights to stop the idle will drop quite low to as much as 3-400rpm but then it picks up again.  From reading the manual I THINK that i might need to adjust the derivative gain but not sure.  Can anyone back this up?

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hi Martin

thanks mate - I've been looking at them and they stand as follows...


I think you mentioned they should be about 50 (midrange) and the car adjusts up or down from that.

I disabled the ISC control sol in pclink, tried setting my car to 700rpm then re-enabling it in pclink again but I just couldn't get the car to adjust really.  In the end I did the same process but adjusted the idle valve so it was closer to 900 base idle which the car seems far happier with.

I have noticed that once warmed up (ie after driving to work down the mway) the car drops to a low idle far less when stopping at lights.  Its just when cold it seems a bit confused heh!

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