Mechanics

ROUGH IDLE/STALLS

1997 Nissan Truck

Engine Performance problem
1997 Nissan Truck 4 cyl Two Wheel Drive Manual 211000 miles

Dear Car Pros,
My engine starts up fine but the idle is very rough and the engine stalls. No 'Check Engine Light' is present at any time. I need to feather or depress the gas pedal to keep it from stalling. If I get the engine to somewhat warm up then it idles(very rough) for 6-10 minutes. When it's cold maybe 2 minutes. The tach shows rpm's on the high end 1800-2k and the low end 500 and below. All avenues lead me to the IACV-AAC valve but have tested it with battery clips and wires to test the solenoid with the AAC attached to it and the solenoid SEEMS to work as I can see the plunger moving in and out as I energize the solenoid.I have cleaned the AAC air passages and throat of the throttle body and MAYBE has helped alittle.I have a Nissan Factory repair cd in pdf and has helped tremendously. But cannot find the problem due to the erratic idle. I can't just throw parts at it as an IACV-AAC is 165 clams from the dealer. Can you help? Thank You!
Avatar
Cliffo
February 11, 2009.




Test the throttle position sensor closed and WOT voltages to include a check on the EGR and PCV valves/Vacuum leaks

Tiny
Rasmataz
Feb 12, 2009.
Dear Rasmataz,
I've completed the resistance checks on the TPS and ALL seems to be fine. According to the repair manual under component inspection, the TPS resistances are: completely closed is approx. 0.5k ohms.I measured 0.71 ohms. Partially open is 0.5-4.0k ohms. I measured 1.25 ohms which falls within the range. WOT is approx. 4.0k ohms. Actual is 4.37 ohms. The truck is fully warmed up so my readings should be accurate on this component but the vehicle still idles rough/stalls. You also asked me to do an EGR check. The EGR itself is new as it's been replaced about 1 year ago. I know it works because the valve does not stick and moves up & down freely. Also, when I push up on the EGR valve it wants to stall the engine. So all checks out there. Now there is a BPT valve with it but I haven't checked it yet. PCV is a mystery part to me as I don't know where that is. I'm guessing under the intake manifold somewhere. The manual doesn't show where that component is. Vacuum lines are all good as they are all attached, intact, not cracked or missing. But I still have the same problem. Rough idle/stalls. And still no " Check Engine Light". Any other thoughts! Thanks!

Tiny
Cliffo
Feb 15, 2009.
Okay-find the IACV-AAC valve and clean it out. It has a PCV valve my references is not showing exactly where it is.

Tiny
Rasmataz
Feb 15, 2009.
Dear Rasmataz,
I've energized the IACV and it appears to be moving up and down. The AAC has been completely cleaned out with isopropyl(rubbing alcohol). With the 2 parts connected, I've energized the IACV and can see the plunger of the AAC unit freely moving. No sticking of the plunger and no broken parts inside. The spring attached to the plunger seems alittle soft on tension but works. The IACV works outside of the truck but don't know if it is actually working when installed. I've ran continuity checks from the ECM to the IACV harness and all seems fine. I've also ran a voltage check from the ECM to the harness with engine off and key on and battery voltage is present. I put the IACV on the test bench and connected it to a variable power supply with 12 volts. It was drawing 1.2 amps of current when I pushed down on the plunger inside the 'sleeve' of the IACV to close the circuit. It 'jumped' when the circuit was closed. In effect, moving the plunger in and out. I've also completely cleaned out the air passages of the throttle body and AAC passages. Looked like molasses in there! Still the problem persists. On the fuel side. I have fuel in the tank, fuel pump works, fuel pressure test checks out, fuel filter not clogged or blocked, all injectors are making a clicking sound when listened to with a stethoscope(mechanic's one), no fuel present when the vacuum line is pulled from the fuel pressure regulator. I ran an inline spark plug tester just to see what the plugs were doing and all checks out there. Cap & rotor seem fine as well. No visible cracks, water or carbon/dirt build up. Now I don't know if the sparks are weak or not but they seem fine. Just so you know, I have a strong background in electronics so I can test the heck out any electrical part. I work in electro-mechanical but more on the electronic side. But I can do medium duty mechanical work as well. So, any advice you give I will follow it exactly. Sorry for the 'book' I just wrote to you but feel you need as much info. As possible as I am detail oriented. Thank You for your time.

Tiny
Cliffo
Feb 16, 2009.
Okay -lets test the TPS, O2, and air flow sensors.

TPS this time -check the closed and WOT voltages not resistances

Tiny
Rasmataz
Feb 16, 2009.
Dear Rasmataz,
I've completed the TPS voltage checks and all readings pass. The O2 sensor checks out as well. The Mass Air Flow sensor looks fine too. After running the truck to warm it up, the DTC P01400 ( EGRC valve ) came up on the dashboard. I checked voltages and solenoid ops and it checked out fine. The MIL turned off without me clearing the code. Now after checking the MAF sensor the code for that component came on(P0100). But all appeared to work within specs. I'm puzzled! Is one part playing off the other? The truck idles somewhat better after it warms up and in the beginning it would stall and die continuously and not even be drivable. Not that I drive it now! I would have to constantly restart the engine. Now, it's somewhat better. But still has a rough idle/ low idle/stalls somewhat less/when cold idle surges. Now I've noticed when the truck is fully warmed up the temp. Guage doesn't even move. It stays at the bottom/below the 'C'. Any thoughts! Thankx! Cliffo.

Tiny
Cliffo
Feb 17, 2009.
Recheck the fuel pressure and injectors

Tiny
Rasmataz
Feb 18, 2009.
Dear Rasmataz,
Sorry I haven't responded lately but I've been
under the weather and moving into a house. I will re-check the fuel pressure and injectors for operations. When checking fuel pressure, do I need the same diameter hose[inner diameter(I.D.)] As the one that is being used on the vehicle? Or can it be a different(larger/smaller diameter?) Thanks again for your help.

Tiny
Cliffo
Mar 11, 2009.
Dear Rasmataz,
Just for informational purposes. The pcv & its connector hose is located directly behind the alternator attached to a small black breather box and the hose is attached directly to the underside of the intake manifold by way of a 90* barbed tube. I checked the valve and it's hose and replaced the valve for the heck of it ($4) and checked/cleaned the hose. It was pretty clean. 3/4" open-ended wrench should do the trick. Closed-end GearWrench worked perfectly for me when re-installing the valve. Also, you must remove the right front tire and go thru the passenger-side wheel well to access the valve. A good light is required here!
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Tiny
Cliffo
Mar 11, 2009.
If you can hook it up without it leaking you're good to go

Tiny
Rasmataz
Mar 11, 2009.

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