TOPIC: 1998 Maxima Grooved, not getting mpg gains, Help.

Hi again Julius, you're Welcome, that's how we do it in GadgetmanLand! And thanks for checking "six" on my hunches!

OK-first check engine thermostat/coolant condition. Flush/clean renew as necessary, then replace the thermo element, check w/ Nissan wrench about possible tweaky procedure for that. Ensure thermo element hoses connected in good condition. This is all to do w/ the fast idle cam. Default for fast idle cam is: engine cold fast idle cam engaged. Engine(coolant)warms up, causing wax pellet to expand, pushing on fast idle cam to gradually reduce idle RPM to hot(curb) idle RPM.

IACV: restricting hose from flat box in air inlet duct to IACV--remove IACV end of hose. Find a few pieces of heater, fuel and vacuum hose such that you fit one inside another forming a short section that will snugly push into the IACV hose straight section, restricting it. Or a short piece of pipe w/ small ID hole in center. Put a clamp around outside of hose to hold inner hose pieces or whatever you can find to use in place. Try to restrict the hose ID down by 80-90% Don't let anything get loose and foul the IACV valve itself! This would be lots easier than removing the IACV itself, and you can easily get back in to adjust the restriction if need be.

Do the Rest of the Stuff if not done already: I don't see a PCV re-route in your pics?? O2 Sensor(s) over 50 K miles replace em, at least get a scan tool connected to check open/closed loop operation look for slow/lazy o2's not switching voltage up/down fast enough, any good mechanic can explain further. If your engine is running cold (thermostat) then that will delay closed loop operation hurting MPG. When all these things are done, then do the computer re-learn Procedure as Ron has said and is detailed on this site, or ask your Gadgetman who did your Groove! Also re-gap the spark plugs increase gap20% over spec, when was last time you looked at the plugs?

Obvious stuff:(pardon if you already mentioned doing this or anything else I'm braying about:P) Clean oil& filt; check tire pressure remove excess weight/stuff in trunk, driving style...'cause after all the Groove stuff is done, the basics still apply, it's all up to You, Julius!!

OK that's all my eyes and brain can do for now, have at it, Julius!!

TracyG Gadgetman Reno

I think I understand what your saying...

Take this hose circled in red and reduce it by 80-90% feeding into the IACV. Right?
Okay, this might be a little hard for me to do since I don't how how to reduce that tube.





I did remove the pcv cap because at first I thought that was my problem...I"ll plug it back in again.

The spark plugs were replaced just about 500kms ago, but I don't gap them. I'll look at this once the TB is working.

Thanks for your help and guidance!

Hi Julius,

Rather than try to find a way to get a smaller hose connected there, you can take a short length (approx. 1" long) of the same size hose, line it with cellophane and pack it with JB-Qwik.

This essentially makes a plug that you can insert into the existing hose.

Before you remove it from "the mold" drill a 1/8" hole through it... now you have your smaller hose.

It needs to be sized for the hose that you have on there so it has a seat against the hose port.

I think I follow..I have to read it a few more times...
But where does the other end go to?
-One end goes to the IACV. OKAY
-The other end? is that just left open with the 1/8 hole or does it connect back to the air filter box.

So the brown part is filled with cellophane and JB-Qwik?

Thanks again.....sorry I have to ask what must be very basic questions, but I'm trying to learn as fast as I can.

You disconnect the hose on the IAC side, insert the plug at that end and put the hose back onto the manifold.

The cellophane is used to keep the JB-Qwik from attaching to the hose.

Use a one inch piece of hose the same size as the hose on the IAC, take a piece of cellophane, lay it on top of the one inch piece of hose and push the middle into the hose with your little finger, thus making a pocket for the plug which you fill with JB-Qwik.

Once it cures, you drill the 1/8" hole through the middle of the plug, then pull the plug and cellophane out of the piece of hose and remove the cellophane.

The plug basically becomes a flow reducer which would be the equivalent of a smaller hose.

Better to ask what could be perceived as "very basic" questions and get it right the first time than to have more to troubleshoot because it wasn't right.

Keep at it.

Karl Fortner
Tacoma, Washington

Julius, reducing the IACV hose doesn't need to be difficult. do this- go to an auto parts store. Ask to see the bulk hose display or dispenser. Many auto parts stores will have bulk heater and fuel and vacuum hoses on spools, sold by the foot.

Get in front of some of these hoses, and examine the different sizes/ Internal diameters. Better still would be if you could pull that IACV hose off your MAxima and bring in with you. With a few minute's playing with this you will see that different size hoses will go inside each other. Might need a bit of spit on 'em... Only and inch or two of the different hoses stuffed together is needed. Won't really matter what type of hose is used as long as is automotive grade(heater, fuel, vacuum). I would not use vinyl or aquarium ,or garden hose that kinda stuff won't live underhood.

Find a size that will fit snug into your IACV hose, then another smaller one that fits into the first one. Just look at the pics for the idea. In my pics the blue and red ones are high grade heater hoses, the thin black is vacuum hose. If there is any doubt they will stay stuffed together just put a screw clamp outside the restriction. I can't say exactly what sizes you need, ya gotta go investigate. If the car doesn't like this much restriction, pull out the smallest hose and see.

NOTE FROM RON: THE CLAMP WILL BE MORE RELIABLE IF IT IS PLACED DOWNSTREAM (TOWARD THE INTAKE MANIFOLD) OF THIS TYPE OF PLUG. THE VACUUM WILL PULL THE PLUG INTO THE RESTRICTION. ADDITIONALLY, A LIGHT COATING OF RTV BETWEEN THE HOSES WILL GIVE YOU BOTH LUBE TO ASSIST IN INSERTION AS WELL AS PROVIDE BONDING AND A SEAL BETWEEN THE LAYERS IN THE EVENT OF A LOOSE FIT.

I havent done this style mod yet, 'cause I've never been lucky enough to have an IAC that is fed air thru a hose! It's a bit unusual, but still lots easier than typical IAC restriction methods, IMHO.

Karl's idea will work too. This isnt real techie stuff, we just want to mostly block the hose ID to reduce the air flow thru the IACV. I'd put the hose pieces,plug or whatever in the straight part that goes on the IACV, cause it's straight and easier to work with than the other end.

I'm not much of a computer guy...adding the hose pics attached was probably as hard for me as copying this idea will be for you, Julius!






TracyG Gadgetman Reno

Okay I got it. I understand what I'm going after. Great instructions and thanks for the excellent explanation.

What I'm a little puzzled is that, if you keep making the hose smaller and smaller, then it won't fit on the other end. (see green circle). The only way is that the small hoses are inside the bigger hose.

If the red circle is 5/8th and the green circle is 5/8th, the only way I see this is by having the smaller hoses inside that hose (doesn't have to be the whole length).

Yes, I like this method better because I can play with the sizes of the hoses if the car doesn't respond well.

So, if I understood my car correctly, the air intake is also taken from the IACV after the TB...meaning car is probably getting too much air and I need to restrict it.

Guys I really appreciate the help. I'm learning things about my car like never before.

Hi Julius,

The main feature of the Idle Air Control Valve is a replacement for the choke on a carburetor. The computer opens the valve enough to keep the rpm's up until the engine is warmer and as the engine reaches temperature the valve reduces its opening.

The reason we want to reduce the size of the air path is that air compresses and as the engine increases its manifold vacuum more air will be drawn in through the IAC opening and if the inlet is 5/8" it allows for much more air to flow reducing the manifold vacuum. By restricting that flow it keeps the manifold vacuum up where we want it.

Depending on the TB style, ie: cabled or Flybywire, the ECU will operate the IAC a bit differently but the primary function remains the same.

Karl Fortner
Tacoma, Washington

Ok, Julius, good! BTW I don't know the ID of your IACV hose, I just used some hoses I have lying around, 5/8" may be close, but you get the idea. If a small Id vacuum hose proves to be too restrictive, you could try a small piece of copper tubing, or brake line tubing in the middle hose, or a vacuum hose connector piece. We are being creative here;)

Karl is correct with what he says he understands the theory of operation Very Well!

BTW thanks for the excellent pics they were instrumental in learning about your Maxima! Cheers!

TracyG Gadgetman Reno