a while ago i adjusted my timing back to where it should be (shop that replaced the distributor didn't set it right) and the idle went up to about 1500 cold and 1100 warm. i tried adjusting the idle how it says in the FSM and i can only get it down to 1100 rpm before the screw bottoms out. i checked the FSM again to see what it says;
check the iacv regulator- couldn't reach it but i doubt that's the problem since it idles higher at warm up then drops when it's warm like it's supposed to.
checked for vaccum leaks- couldn't find anything
check throttle body- it was clean last time i checked it, it works smoothly, and there a little bit of slack in the line.
i don't know what else to check. i guess i could just back off the timing a little, but that's no fun. if anyone has any ideas on how it could be related to the timing or how i can get more adjustment in the idle adjustment screw, that would be great.
high idle, can't adjust it any lower
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stash420sx
- Posts: 124
- Joined: Fri Sep 20, 2002 1:05 pm
Mine was doing the same thing recently. It was the coolant temp sensor. The ECU was thinking the engine was ice cold, even when it was warm, so it kept the idle high all the time. It didn't throw a code either - I just had a hunch and replaced it. Boom, problem solved.
See if you are running rich also, even after warmup - if so then you probably want to check/replace both the O2 and coolant temp sensor. Neither is that difficult or expensive to replace.
If your idle is consistent, more than likely the MAFS is working ok, so I would check the other two sensors first.
See if you are running rich also, even after warmup - if so then you probably want to check/replace both the O2 and coolant temp sensor. Neither is that difficult or expensive to replace.
If your idle is consistent, more than likely the MAFS is working ok, so I would check the other two sensors first.
th o2 sensor is new from a week ago so that's not it. i doubt i'm running rich because my mileage is really good (30 mpg on the highway) how would i check that aside from looking at the exhaust? the warm up idle speed isn't controled by the ecu, the IACV has a metal strip that reacts to the heat and closes a door. i'll check the coolant sensor anyway, it's worth a shot.
edit, i checked the coolant temp sensor, it read about 320 ohms when the engine was warm and the electric fan kicked on when i unplugged it. a few times in the FSM it mentions using a computer to set the idle, could i put the screw back in the middle and use the computer to reset the idle control system? or maybe i could just reset the ecu. i think i'll try that now.
edit, i checked the coolant temp sensor, it read about 320 ohms when the engine was warm and the electric fan kicked on when i unplugged it. a few times in the FSM it mentions using a computer to set the idle, could i put the screw back in the middle and use the computer to reset the idle control system? or maybe i could just reset the ecu. i think i'll try that now.
how your idle control works here. The screw you turned is in the IACV. moving the screw changes how much air is allowed into that valve. If you were to screw it all the way in the car would die because there is no air getting into the engine through the IACV. At Idle that is the only place air comes from unless its cold Then the FICD is allowing additional air in. once the car warms up the FICD closes and no more air is allowed in there. I bet you see where this is going huh? You have a vaccum leak or a partially stuck open FICD[not likely since it does change your cold idle].
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s13sr20chris
- Posts: 4148
- Joined: Tue Jun 10, 2003 9:32 am
- Car: '89 Nissan S13 w/redtop running 13psi and not leaking fuel anymore
- Contact:
hey nistech,am i correct in thinking that the idle screw only changes base idle? in which case, the iacv stepper motor or pulse width operated motor could be overcoming his idle screw being all the way in. i am not sure off the top of my head. if you want to adjust your idle and timing, unplug the tps.
NISTECH, could it be like meantime said and be the coolant temp sensor? Im running rich (running rich is causing misfiring) and my idle also stays solid at about 1-1k RPMS (the lowest I could get it was 1-1k) and my o2 sensor was bad, so I replaced it. My car has also adjusted it's idle to the proper speed of 750 RPMS sometimes.
That's exactly what mine did, Neejay -
On really hot days, or when the engine was really working in traffic, the idle would adjust back down to 750. Which indicated to me that the fault was not with the IACC system, but with the ECU not getting the mixture or idle correct. And I had just replaced my O2 sensor also.
All the other times, it would stay at 1000 - 1100 and run rich, misfire, bog under acceleration, etc.
Try replacing the coolant temp sensor, it's $28 from Nissan (for DOHC) and takes all of about 5 minutes to swap out.
On really hot days, or when the engine was really working in traffic, the idle would adjust back down to 750. Which indicated to me that the fault was not with the IACC system, but with the ECU not getting the mixture or idle correct. And I had just replaced my O2 sensor also.
All the other times, it would stay at 1000 - 1100 and run rich, misfire, bog under acceleration, etc.
Try replacing the coolant temp sensor, it's $28 from Nissan (for DOHC) and takes all of about 5 minutes to swap out.
Worth a shot then...Where is the coolant temp sensor?Meantime wrote:That's exactly what mine did, Neejay -
On really hot days, or when the engine was really working in traffic, the idle would adjust back down to 750. Which indicated to me that the fault was not with the IACC system, but with the ECU not getting the mixture or idle correct. And I had just replaced my O2 sensor also.
All the other times, it would stay at 1000 - 1100 and run rich, misfire, bog under acceleration, etc.
Try replacing the coolant temp sensor, it's $28 from Nissan (for DOHC) and takes all of about 5 minutes to swap out.
it's right on the front of the intake manifold, it screws into the neck where the top radiator hose goes into the block. it's the one on the left, the one on the right is for the water temp gauge.
that doesn't really sound like my problem, my car doesn't bog and i've never notice it drop on hot days. my electric fan kicks on occasionally when the car is just sitting (no clutch fan) like it's supposed to. and i checked the resistance on the sensor, it read 320 ohms, which is right were it should be.
i've been working on the car all day and i think i found a solution to my problem. it involves a high cliff and a few buddies to help me push...
that doesn't really sound like my problem, my car doesn't bog and i've never notice it drop on hot days. my electric fan kicks on occasionally when the car is just sitting (no clutch fan) like it's supposed to. and i checked the resistance on the sensor, it read 320 ohms, which is right were it should be.
i've been working on the car all day and i think i found a solution to my problem. it involves a high cliff and a few buddies to help me push...
no really, i have been working on the car for a while. i checked all the vaccum lines, took off the iaa unit and cleaned it and checked the throttle body. i put everything back together and nothing, exact same thing.
i tried pinching the thick hose that goes from the intake right before the throttle body back to the iaa and the iacv. that is supposed to be the only passage for air around the throttle body so pinching that off should kill the engine. when i pinched it nothing changed at all, the idle didn't even drop.
the only thing i noticed that did anything was turning the distributor back to the left to retard the timing a lot.
on a side note i noticed that when i had the timing where it should be the engine would miss occasionally. it made a really small noise almost like a soft honk and the engine would shake a little. i could hear the noise out of the exhaust a little better, kind of like a weird rush of air or a honk again. i assume it was a miss, or maybe knock, i'm not sure. it went away when i retarded the timing.
i tried pinching the thick hose that goes from the intake right before the throttle body back to the iaa and the iacv. that is supposed to be the only passage for air around the throttle body so pinching that off should kill the engine. when i pinched it nothing changed at all, the idle didn't even drop.
the only thing i noticed that did anything was turning the distributor back to the left to retard the timing a lot.
on a side note i noticed that when i had the timing where it should be the engine would miss occasionally. it made a really small noise almost like a soft honk and the engine would shake a little. i could hear the noise out of the exhaust a little better, kind of like a weird rush of air or a honk again. i assume it was a miss, or maybe knock, i'm not sure. it went away when i retarded the timing.
well it came to me right after i made that last post, if it's not going around the throttle body, maybe it's going through it. i just backed the closed position set screw out all the way and problem solved. it idles right at 700 rpm with the timing advanced and the idle screw all the way in. (not where i would like it but it works so who cares)