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The problem my friend is having is a low idle miss and some surging it jumps from 800 at idle to about to 1100. He has had to replace the TPS not sure if he adjusted it his Crank angle sensor he just did a tune up plugs plug wires cap and rotor. the truck runs better from what i can tell put still has this problem. Any suggestions.
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this sounds like a vacuum leak. I would start by checking for any bad vacuum hoses. if this has a throttle body I would spray around the base of the t/body with carb or t’body cleaner and see if the engine idle speed changes.
I thought the same thing we done that nothing no change at all. checked all the vacuum lines all are good not dry rotted or split.
You really need to use a vacuum gage over trying to do a visual inspection. The most effective way to check for vacuum leaks is a smoke machine.
Does the vehicle also have this RPM increase when he leaves the truck in gear at a stop or even in neutral?
If you had a stuck open EGR valve, that would cause rough running conditions at idle until you drove at a cruising speed.
Did you inspect the IACV?
And what brand plugs did he use as Nissan vehicle like NGK’s.
Also, was this issue present before the tune up?
the issue has been there for a while we thought a tune up would fix his problem his plugs and plug wires were bad the cap and rotor were horrible. we used a smoke machine but never saw any leaks. He has a TPS not sure of a IAV and the plugs came from motion auto store we get a discount there. I don’t remember the name brand.
I would start with any check engine lights you might have and then I would start checking for air in the cooling system
http://www.youtube.com/watch?v=zUpXgAJ1gjU
Then check for vacuum leaks
http://www.youtube.com/watch?v=9CPqbaSgcok
and if I didn’t have success with any of those I would check the scan tool data to see if the TPS read close to 1v when the throttle was closed and about 5v when the throttle is all the way open.
Well I just saw that was an 87, if this is true it I think it would have a carburetor on it, is it really an 87 and does it have a carburetor?
It has a Throttle body on it like a carb and the other test didn’t help it was good to those standards when i checked my egr valve it was almost closed off with gunk but now it is clean and still no change
EGR will not effect the idle unless it’s stuck open. I still have the question though does it have a carburetor on it?
OK thanks for that. It will take more than just a visual inspection to find a vacuum leak, I would suggest checking for them as I show in the video link I posted. Also it’s important that the cooling system is in good order so please check the other link about bleeding the cooling system, if there is air in the cooling system it can also cause a fluctuating idle. Lastly you might try tapping on the idle air control valve with the handle of a screwdriver or something as the engine is running to see if that causes any kind of change, if it does then you could have a problem there. Lastly if there is an idle adjustment screw don’t mess with it as this could also offset the idle mix enough to cause that problem.
He adjusted the screw that you said not to but it was after we replaced it so the thing is that how do i readjust it properly and or how do i explain it to him to do? the coolant doesn’t have air like your youtube video and the smoke test on it showed a left side exhaust gasket was leaking needs a new donut gasket othet than that nothing
If the exhaust leak is before the O2 it can offset the mix and possibly cause a problem. I can’t remember but have you checked for vacuum leaks using something other than smoke?
no i have not i don’t know if he has or not i will fix the exhuast leak and see about checking for a vacuum leak
Im not sure if this will work on your vehicle or not but, on some vehicles, you can unplug the IACV, then adjust the throttle screw until your RPM’s read around 700 to 800 for an Auto. Once your there, turn the vehicle off, reinstall the IACV plug and take it fro a long test drive so the computer can adjust.
This may or may not work on your Nissan..
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