Low idle. Not vaccum leak, not IACV.
10-05-11, 02:18 PM
#1
Lexus Champion
Thread Starter
Low idle. Not vaccum leak, not IACV.
UPDATE: Page #3, Post #31
So I've had the (seemingly normal) low idle problem on my 1999 SC400. Searching has led me to look at vaccum leaks and cleaning out my IACV, both of which my mechanic did for me during my last oil change. He said there was no vaccum leak (by listening to the engine, he said he could not hear one), and he sprayed the inside of my throttle body (I think thats what its called) with cleaner. That didnt help either.
Car runs flawlessly, other than an occasional CEL for a bad front cat. What else should I look at to diagnose the low idle?
So I've had the (seemingly normal) low idle problem on my 1999 SC400. Searching has led me to look at vaccum leaks and cleaning out my IACV, both of which my mechanic did for me during my last oil change. He said there was no vaccum leak (by listening to the engine, he said he could not hear one), and he sprayed the inside of my throttle body (I think thats what its called) with cleaner. That didnt help either.
Car runs flawlessly, other than an occasional CEL for a bad front cat. What else should I look at to diagnose the low idle?
Last edited by scENFORCER; 01-05-12 at 03:21 PM.
10-05-11, 06:31 PM
#6
Lexus Champion
Thread Starter
I do have a brand new transmission mount though, and the engine mounts are fine.
..and I have a ' Fuel Injection Idle Air Control Valve', whatever..
Last edited by scENFORCER; 10-05-11 at 06:49 PM.
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10-06-11, 04:28 PM
#11
Lexus Champion
Thread Starter
The car runs smoothly and flawlessly. No misfire or shaking at any point. Simply a low idle.
10-07-11, 04:01 PM
#15
how low of an idle are we talking about, basically where does the needle point to?
if you have had your cluster out recently the needle could also just need to be calibrated.
you can try adjusting the throttle plate stop screw and give it a few turns whichever direction is opening your throttle body and see if it stabilizes your idle some.
really not very much just like 2-3 turns and remember how many you do total so you can set it back if you want later to stock.
you want to adjust this on a fully warmed up engine, and if it seems to be working turn it till you get in the 750rpm area with the a/c on.
if not then set it back to how it was.
adjusting the tension on the throttle cable to let in more air will give the tps the wrong reading. above is the right way and if you do more than a few turns then yes you will need to remove the slack in the cable using those 2 adjusting nuts.
If all your mechanic did was spray cleaner into the throttle body, he really did nothing at all.
on an sc400 the IACV is entirely separate from the throttle body.
When cleaning the IACV its a good idea to manually check if the plunger still goes up and down, you do this by turning it.
If you cannot turn the plunger easily, that is your problem. they get stuck and those magnets in the base cant move them anymore.
some people just clean the plunger tip, clean the passages and put it back together without checking the plunger.... not good enough.
the fix in that case is to open up hit it with wd40 all over the plunger arm and let it run down towards the base.
Give it a bit and attempt to turn it till it brakes loose and spins freely which you may have to add more wd40 or grease of your choice to get a stuck one to do that. it should be able to spin freely with minimal effort, like 1 finger.
Its like 2 bolts and 3 phillips screws, its to the side of the throttle body and really easy to remove. you may want to DIY on this one.
if you have had your cluster out recently the needle could also just need to be calibrated.
you can try adjusting the throttle plate stop screw and give it a few turns whichever direction is opening your throttle body and see if it stabilizes your idle some.
really not very much just like 2-3 turns and remember how many you do total so you can set it back if you want later to stock.
you want to adjust this on a fully warmed up engine, and if it seems to be working turn it till you get in the 750rpm area with the a/c on.
if not then set it back to how it was.
adjusting the tension on the throttle cable to let in more air will give the tps the wrong reading. above is the right way and if you do more than a few turns then yes you will need to remove the slack in the cable using those 2 adjusting nuts.
If all your mechanic did was spray cleaner into the throttle body, he really did nothing at all.
on an sc400 the IACV is entirely separate from the throttle body.
When cleaning the IACV its a good idea to manually check if the plunger still goes up and down, you do this by turning it.
If you cannot turn the plunger easily, that is your problem. they get stuck and those magnets in the base cant move them anymore.
some people just clean the plunger tip, clean the passages and put it back together without checking the plunger.... not good enough.
the fix in that case is to open up hit it with wd40 all over the plunger arm and let it run down towards the base.
Give it a bit and attempt to turn it till it brakes loose and spins freely which you may have to add more wd40 or grease of your choice to get a stuck one to do that. it should be able to spin freely with minimal effort, like 1 finger.
Its like 2 bolts and 3 phillips screws, its to the side of the throttle body and really easy to remove. you may want to DIY on this one.
Last edited by Ali SC3; 10-07-11 at 04:17 PM.