My 2000 Nissan Frontier sometimes fluctuates at idle after warm-up. I was thinking perhaps egr tube carbon build-up? Problem is I don't know if there are access ports to clean-up? If so I can't seem to locate them.

You should be able to find vacuum hose routing sticker in the engine compartment.
http://www.nissanpartsdeal.com/parts-list/2001-nissan-frontier/engine-control-vacuum-piping.html?Diagram=223_A001

Not easy to see, but on drivers side of engine underneath intake manifold, so look for airflow intake tube, the larger air tube, and it is just below and to the firewall about middle of engine top to bottom. Hose comes out of it and two bolts hold it in, pretty easy to see once you know where it is located, but difficult to change. Sometimes just cleaning hose out will solve problem. Worth a try to buy EGR cleaner and spray and run a wire inside hose to loosen up carbon.
CERACOAT-NANOTECH.com

you should clean the egr first and see if that helps.
egr is most likely your problem.
its going to have a build up of carbon and sometimes it will be so restricted that your car cannot run.

that will fix your problem i bet.
good luck

A high rev problem is due to either carbon build up in the iac passage's not letting the iac close to normal idle or the iac is just bad and stuck in that position.

iac= idle air control solenoid

Inside the throttle body intake is a butterfly and just above that is a small opening that the iac uses to move air past the butterfly and this sometimes gets plugged with carbon build up so spray some carb cleaner down through the passage,and sometimes you have to remove the 4 bolts and take the throttle body off to clean them out.

Saturns are known for carbon problems,and they are hard on egr systems,I recommend using sea foam a couple times a year to help fight the carbon build up,just follow the direction and use it in the fuel and vaccum lines as directed but do it on a warm engine and let sit for a couple hours so the sea foam has time to loosen the carbon

Is there a symbol that looks like a key on the display?
If not then you may wanna check the IAC motor know as the Intake Air Control Valve, Unplug it and see if this helps it run, if it runs but fluctuates the idle then there is your proble, if it does not change check the egr tube for carbon build up. hope this helps

Hello and thank you for using Fixya!

I know you say there is nothing clogged. How ever, it's very common to get a Egr code P0400 when the egr tube is clogged. Remove just the Egr tube, the one with the egr temp sensor. Remove the EGR temp sensor and remove any carbon build up in the pipe. Then make sure the passeges in the intake are clear also.

If you have any more questions on this, please feel free to ask. Thanks Jay!

remove the egr valve clean out carbon build up in the intake port where the egr valve goes.use a piece of old clothes rack.then clean up debris.

Check for

vacuum leaks on intake manifold,

the air tube between the air filter.

intake manifold vacuum hose.

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clean throttle plate with Berryman carburator cleaner

SEE sample picture HERE
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Also remove carbon built up behind the EGR valve and the EGR passage tube.

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Vacuum leak WILL offset the intended 14.7 to 1 air fuel ratio.

More un-metered air (leaks) will lean out the fuel mixture.

Use small amount of Berryman carb clearer at potential air leak area will help you identify trouble spot.

At idle,just spray and listen for the RPM surge.

The in-rush of carb clearer will increase the RPM on the motor.

Record the problem spot(s) and address it later.

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EGR carbon built up require 2+ hours to clean from start to finish.

You will need a new EGR base gasket before your start.

Locate and remove the EGR valve after the vehicle is cool down.

Carefully record the connector and vacuum line (for older vehicle) location by drawing an easily to follow diagram.

Remove the EGR valve.

Inspect the location of the carbon built-up inside the valve and the EGR passage tube.

SOAK these areas with WD-40 spary.

You will need a small screwdriver,cloth hanger and lot of newspaper and time to get this cleaning done right.

RE-SOAK the carbon and let it sit for over-night will also help.

One the last round,pass a shop vacuum of the EGR valve and the passage pipe.

Install the new EGR gasket and connectors.

Allow the vehicle to warm up outdoor to burn up any remaining WD-40.


Take it for a test drive.


Please rate my answer if it's useful to you.


Cheers,

Mustgo

P1400 on your vehicle is described as :Differential Pressure Feedback EGR Circuit Low Input You either need a new DPFE valve, or a new EGR valve. Both can be tested for functionality before replacing them both. EGR valve is more likely I think. Cleaning it may not improve its performance, but its worth a try. Also check the vacuum lines between the DPFE and EGR system. The EGR valve and DPFE are usually close together above the exhaust manifold/downpipe. you need service instructions to test these items, suggest you go to a garage really...

Check for vaccume leaks and also you PCV valve. check the hose too. Visually inspect every vaccume hose you can find. Sounds like a leak .