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Old 08-01-2014, 11:30 PM   #1
ahardb0dy
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Default 93 KA new problem

This morning the truck ran great, best it has so far except when I stopped I noticed the RPM's won't go below 1100 RPM, AC on or not, actually when I turn the AC on they go lower.

Moved the truck at lunch same thing, than same on the way home.

Any idea what to check? Will check for codes tomorrow, replaced 90% of the vacuum lines already.

Would cleaning the MAF sensor with carb cleaner hurt it?


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Old 08-01-2014, 11:33 PM   #2
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They make cleaner specifically for maf sensors. I was gonna suggest to check for vacuum leaks and check the thermo element plunger deal on the back of the throttle body.
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Old 08-02-2014, 03:03 AM   #3
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I know about thermo elements, wasn't aware this engine had it, will look into it, thanks.

I usually use MAF cleaner, was out so I used the carb cleaner, have to pick some up.
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Old 08-02-2014, 03:24 AM   #4
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I may be using the wrong terminology. And I'm not 100% certain that the 93's have them. It's a thermal device of some sort on the back of the throttle body. It has coolant going across a spring and it affects the idle. I'm too lazy to go look at the FSM
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Old 08-02-2014, 04:09 AM   #5
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My 87 HB and 90 sentra had them, have to check the FSM if I can stay awake long enough. Been busy over here, wife broke her leg Sunday so she can't do anything.
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Old 08-02-2014, 05:36 AM   #6
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If you suspect a bad Maf the disconnect it wit the engine running and if it idles better than its signal voltage to the ecm is skewed and the ecm can't correctly calculate the mass of air entering the cylinders so the engine will run rough as the stochiometric air fuel ratio of 14.7-1 cannot be reached and it I'll
Ground the fuel injectors for too long affecting combustion and therefore engine performance.

Also check your idle air control valve aka iac located on the
throttle body, it allows a certain amount of air to bypass the throttle plate at idle to keep the engine idling. After thousands of miles carbon buildup causes the pintle inside to not move far enough and allow air to bypass the throttle plate. Take it off and clean it with brake parts cleaner then put back on and re test. Sometimes the stepper motor goes bad and its time for replacing.

Check all vacuum hoses for cracks and leaks as heat from the engine bay dries them out. If they are bad they will lean out the air fuel ratio too much and cause incomplete combustion as leaner mixtures are harder for the spark plugs to burn off. Spray brake parts cleaner around the hoses and if any is drawn in then you found your leak.

Also take your egr valve out and apply vacuum to it with a vacuum gauge, if it doesn't hold vacuum it needs replacing. Also scrap the port out with a screwdriver, over thousands of miles carbon buildup causes the valve to stiick open which leans out the air fuel mixture causing a rough idle.

With a multimeter set to ohms measure the resistance of your fuel injectors, if any of them read o.l then they clogged and have too much internal resistance and need replacing as they not flowing fuel. Never a bad idea to replace our fuel filters as they the injectors best friend and keep them from clogging up.

Hope this helps you bro good luck figuring it out
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Old 08-02-2014, 05:44 AM   #7
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And Alabama lowlife is right there's a fast wax thermo valve located near the throttle body that uses coolant to expand a wax type pellet and allow air to bypass the throttle plate..... worth checking it out
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Old 08-02-2014, 03:54 PM   #8
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I found it in the diagram in FAST, didn't see it ( or the TB in the FSM),
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Old 08-03-2014, 04:55 AM   #9
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Pulled the AIV today and cleaned it best I could, gasket was coming apart so I put a thin layer of copper RTV on it than re-installed it. Found the thermo element and backed the adjusting screw back slightly. At least if the thermo element is not receding like it should this way the idle will be lower until I can replace it.

So far the idle is lower, sitting right at 900 with the AC on and about 800 with AC off.

I checked the idle with the hose from the valve cover plugged and not connected to the air cleaner lower housing as I did not have a long enough hose, I do now so tomorrow will add the hose and see how it is.

Have to check for codes tomorrow also.
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Old 08-03-2014, 05:10 AM   #10
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Getting better bro keep plugging away you will eliminate the problem and when you do let us know what it was to help fellow members out
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