Guest 2JZ GE W58 Posted November 3, 2013 Share Posted November 3, 2013 Ok so since i got my 93 NA its been idling around 1100rpm. Occasionally it drops to around 500rpm idle after driving somewhere and in danger of cutting out, but after switch engine off & restart its back to 1100rpm. This says dodgy sensor to me (ISCV?) Another quirk is when its warming up, idling around 1600-1800rpm (lights, radio, aircon dependent) and i blip the throttle, instead of revs dropping and landing back at 1600rpm or so again when i let go the throttle, they drop right to 1100 or so and straight back up to 1600 then to continue warmup. Now it sounds like the ISCV is slow to cut in after the throttle is closed (ISCV or TPS dodgy?) I got a cheap 94 from japan for spares (i needed a lot), idled fine at 800 so i robbed the ISCV from that. But this didnt fix the problem......... SO now im wondering what else is in the idle speed control loop. From what i can see the TPS closes a connection when the throttle is closed, and this through the ECU opens the ISCV to let some air bypass the throttle butterfly valve and into the motor. ANyway i checked TPS function as per the manual and seems fine Does anyone know what else is in the idle speed control loop? i.e. how does ECU know what rpm the engine is at, is it just by throttle position? thanks for any input Quote Link to comment Share on other sites More sharing options...
Ian C Posted November 4, 2013 Share Posted November 4, 2013 Once it's warmed up, overfuelling can cause a low idle and possible stalling, so check the O2 sensor's output. The throttle position sensor has an idle switch (IDL) that tells the ECU that it should switch to idle control strategy. If the TPS isn't adjusted properly, it'll never trigger this switch even though the testing will say it works properly. Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted November 4, 2013 Share Posted November 4, 2013 cheers Ian, doubt it 02 related as the plugs are pretty white i.e. looks lean if anything. think i'll swap over the TPS from me spares car and see if that reads right, the current one passes the continuity test but not the resistance test Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted November 9, 2013 Share Posted November 9, 2013 ok so i swapped over the TPS off the spare car and boom it fixed the warming up rev drop quirk, but even after spending ages adjusting the TPS to the right settings (as per the manual and the thread on forum) now it idles at about 1400rpm. so unless anyone can offer another possible faulty item in the idle speed control loop, i must get another ECU to swap it out?? Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted November 10, 2013 Share Posted November 10, 2013 May sound a bit obvious, but is the throttle closing fully? Or a vac line leak AFTER the throttle flap, as this would presumably cause increased idle speed? Quote Link to comment Share on other sites More sharing options...
David P Posted November 10, 2013 Share Posted November 10, 2013 Check the closed circuit oil breather valve. Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted November 10, 2013 Share Posted November 10, 2013 May sound a bit obvious, but is the throttle closing fully? Or a vac line leak AFTER the throttle flap, as this would presumably cause increased idle speed? throttle closes alright yes. i had a look at all vac lines, appear ok, regardless i doubt its them anyway because now and again the idle will drop to around 500 or that - and switching car off and back on again cures that - which makes it appear (imo) to be electrics related problem... Check the closed circuit oil breather valve. where would i find that? Quote Link to comment Share on other sites More sharing options...
David P Posted November 10, 2013 Share Posted November 10, 2013 Top rear of n.s. cam cover. Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted November 10, 2013 Share Posted November 10, 2013 what is n.s.? and could you tell me what a closed circuit oil breather valve (iv never heard of one) have to do with idle speed? Quote Link to comment Share on other sites More sharing options...
David P Posted November 10, 2013 Share Posted November 10, 2013 Near side. If it's buggered it could be letting in air at tickover. Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted November 10, 2013 Share Posted November 10, 2013 (edited) could you tell me what a closed circuit oil breather valve (iv never heard of one) have to do with idle speed?It's part of what's often called PCV - Positive Crankcase Ventilation. Basically oily air is sucked out the top of the cam covers into the intake, often via a valve and/or filter, to get rid of any blow-by gasses etc. That's why a leak from the hose or valve could increase the tickover (and even removing the dipstick can have a similar effect) But if your tickover problem is INTERMITTENT, I would agree that it's probably NOT a Vac leak, but an electronic fault. Which COULD of course be a faulty ECU, but I would suspect the connectors on the engine. Get some switch cleaner, cotton buds, matchsticks, and give them all a good clean (especially the ones on the TPS, ISCV, CPS etc) Edited November 10, 2013 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted November 20, 2013 Share Posted November 20, 2013 It's part of what's often called PCV - Positive Crankcase Ventilation. Basically oily air is sucked out the top of the cam covers into the intake, often via a valve and/or filter, to get rid of any blow-by gasses etc. That's why a leak from the hose or valve could increase the tickover (and even removing the dipstick can have a similar effect) But if your tickover problem is INTERMITTENT, I would agree that it's probably NOT a Vac leak, but an electronic fault. Which COULD of course be a faulty ECU, but I would suspect the connectors on the engine. Get some switch cleaner, cotton buds, matchsticks, and give them all a good clean (especially the ones on the TPS, ISCV, CPS etc) ok i tried that breather valve, i blew into it from intake side and met a dead end, sucked on it and felt a click and air came through. seems legit. more info - it used to idle around 1100rpm before, and since i adjusted the TPS according to the thread here/manual it now idles around 1500. and sometimes now when i start up it idles at 1000, then after i drive away it will idle at 1500 again. something electric is amiss, but what? Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted November 21, 2013 Share Posted November 21, 2013 Well why don't you try cleaning all the electrical connectors on the engine, like I suggested?! (I do it as a matter of course every couple of years on every car I've owned . . . it's called preventative maintenance) Quote Link to comment Share on other sites More sharing options...
Guest 2JZ GE W58 Posted December 29, 2013 Share Posted December 29, 2013 it turned out to be the ISCV. depsite putting one from a normal idling car onto it, it still idled high. ISCV had to be opened up and the valve plunger turned out a couple mm to close the throttle butterfly valve bypass hole a little more and slow the engine idle speed down a tad Quote Link to comment Share on other sites More sharing options...
Stephen Everett Posted May 25, 2014 Share Posted May 25, 2014 Hi, i have an identical problem with my, 95 n/a. What's a ISCV and where can I find mine please? Quote Link to comment Share on other sites More sharing options...
Bayden_uk Posted May 25, 2014 Share Posted May 25, 2014 Hi, i have an identical problem with my, 95 n/a. What's a ISCV and where can I find mine please? is the one on the left ste 2JZ, how did you get to the bottom screw. not got alot of tools after my landrover was stolen and they were in the back, im struggling to get to the bottom screw without killing it Quote Link to comment Share on other sites More sharing options...
David P Posted May 25, 2014 Share Posted May 25, 2014 That one is always TIGHT, take the t.b. off and then it can be un-nipped using mole grips. Quote Link to comment Share on other sites More sharing options...
Bayden_uk Posted May 25, 2014 Share Posted May 25, 2014 that one is always tight, take the t.b. Off and then it can be un-nipped using mole grips. t.b. ? Quote Link to comment Share on other sites More sharing options...
David P Posted May 25, 2014 Share Posted May 25, 2014 Throttle body. Quote Link to comment Share on other sites More sharing options...
Bayden_uk Posted May 25, 2014 Share Posted May 25, 2014 Throttle body. ah ok... is it a simple enough job? Quote Link to comment Share on other sites More sharing options...
David P Posted May 26, 2014 Share Posted May 26, 2014 If you can undo half a dozen 12mm bolts? Quote Link to comment Share on other sites More sharing options...
Kamron Posted May 26, 2014 Share Posted May 26, 2014 ah ok... is it a simple enough job? Hi Bayden, Relatively simple. 10 minute job. See link: http://www.mkivsupra.net/vbb/showthread.php?4262-S-Plugs/page3 Post 37 has pic reference. Just lever up TB to get more access to those screws. Quote Link to comment Share on other sites More sharing options...
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