I30 1998 Auto with an idle stumble problem

[zul8tr]

I have an unusual (to me) problem. When engine warmed up and ideling in drive with foot brake on the engine has intermittant stumbles where there is a noticable drop in rpm. It doesn't do it continuously. However in neutral the is never a stumble/rpm drop even if ideled for a long time. The are no codes on the ECU. I have not checked the transmission codes. The car has good power with no misses under accelleration.

Any thoughts for a diagnosis and fix are appreciated.

Thanks

[MinisterofDOOM]

You probably need to clean your idle air control valve (IACV).http://www.moodym.com/maxima/c...l#IAC

[zul8tr]

You probably need to clean your idle air control valve (IACV).http://www.moodym.com/maxima/c...l#IAC

I will give that a try.

Also I need to replace the valve cover gaskets so I will have the manifold off and the IACV will be easier to get at.

Any tips on removing the intake manifold that has numerous hoses about the throttle body and at the rear valve cover some tricky support bolts and some other 2 bolts at the lower drivers side corner of the valve cover?

Thanks

[NutriaforBreakfast]

I would tend to be your emmissions system needs cleaning up firstlike the Minister says.

I used masking tape to create a reference system. I would put tape onthe hose with "a" and the hose barb would have "a" etc etc. Buy a cheap plastic organization box with small and large trays and putyour parts in it. Take pictures before disassembly if needed.

You are going to remove the UPPER intake, also called the plenum,to change the valve cover gaskets. The lower intake manifold needsto stay put. I would put on a new EGR valve and new water hoseswhile you have that stuff pulled off. If that stuff breaks while youare on a road trip, the disassembly $ will be too high.

The plenum will have an EGR tube (not the valve) at the back of it.It could be clogged with carbon so clean it out. The plenum is a littlehard to get off because of the lack of room due to the firewall but bepatient. I actually took a 2x6 piece of wood and laid it down on theedges of the car hood area to do this easier. The EGR valve is a paintoo so have patience.

You will want to clean your throttle body too.

Dont submerge any parts in cleaner or be to crazy on carb cleaneras this stuff can hurt your electrical parts. Dont mess with the MassAir Flow Sensor at this time.

Good luck. I know if i can do it u can 2

[zul8tr]

I would tend to be your emmissions system needs cleaning up firstlike the Minister says.

I used masking tape to create a reference system. I would put tape onthe hose with "a" and the hose barb would have "a" etc etc. Buy a cheap plastic organization box with small and large trays and putyour parts in it. Take pictures before disassembly if needed.

You are going to remove the UPPER intake, also called the plenum,to change the valve cover gaskets. The lower intake manifold needsto stay put. I would put on a new EGR valve and new water hoseswhile you have that stuff pulled off. If that stuff breaks while youare on a road trip, the disassembly $ will be too high.

The plenum will have an EGR tube (not the valve) at the back of it.It could be clogged with carbon so clean it out. The plenum is a littlehard to get off because of the lack of room due to the firewall but bepatient. I actually took a 2x6 piece of wood and laid it down on theedges of the car hood area to do this easier. The EGR valve is a paintoo so have patience.

You will want to clean your throttle body too.

Dont submerge any parts in cleaner or be to crazy on carb cleaneras this stuff can hurt your electrical parts. Dont mess with the MassAir Flow Sensor at this time.

Good luck. I know if i can do it u can 2

Thanks for the tips

I just Ohmd the IACV and got about 30 ohms at 70 degrees F at the connector for all the combinations of pin testing noted in my Haynes manual (pins 1 to 2, 2 to 3, 4 to 5 and 5 to 6). Thus the unit has the correct ohms. I have a 92 300 ZX and have used WD 40 in the IACV to help with idle issues. Can I do that with the I30? If so where would it be injected?

Upon further inspection of the back of the engine at the EGR tube connection at the driver rear of the plenum I noticed a rubber hose that starts there but attached to the plenum and goes to the EGR valve. How on earth do you get at the squeeze clamps to remove the hose connection at the plenum? Is this a cut job and replace later but putting on the clamp will still be a problem.

I have had the plenum off my 300 ZX to replace injectors but that now seems easy compared to this I30 plenum. I have already done the front valve cover - that was a breeze.

Thanks again

[NutriaforBreakfast]

I ohmed my IACV and it ohmed ok BUT it was so carbonedup it wasn't working. I think there is a technical article on thiswebsite to help you.

I dont think its a hose but a metal tube that connects to the backof the plenum.(If it is a hose, its one heck of hose not to melt with exaust gas.)There is a flange on the plenum held on with bolts in the firewall area.

[zul8tr]

I ohmed my IACV and it ohmed ok BUT it was so carbonedup it wasn't working. I think there is a technical article on thiswebsite to help you.

I dont think its a hose but a metal tube that connects to the backof the plenum.(If it is a hose, its one heck of hose not to melt with exaust gas.)There is a flange on the plenum held on with bolts in the firewall area.

Upon further looking (hard to really see behind the rear of the engine with mirror and light) the rubber hose does not go to the EGR. I believe now that it is part of the coolant circulation to the throttle body. So here is the route suspected.

Looking at the back of the engine (rear looking forward) a hose comes from the throttle body and connects to the plenum just to the left side of the EGR tube that has 2 bolts that secure it to the plenum. From there there is about 1.5" of plenum and on the left side of the EGR tube the approx 4" long rubber hose continues and makes a sweeping 180 degree turn back toward the EGR tube and connects to a metal (~6mm dia. tube) near where the EGR tube bolts to the plenum. From there the metal tube route is difficult to figure but it appears to go toward the front of the engine to complete the circuit to get coolant to flow.

It is this 4" hose that I am asking about its removal and reinstallation.

At both ends the hoses have the typical spring clamps.

Thanks again