1997 Nissan Truck Rough Idle/Stalls

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!

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.

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.

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.

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!

Dear Rasmataz,
I just have a fuel pressure gauge from Kragen Auto. It's a low budget one but I feel it should be fine. It also reads vacuum as the gauge is divided in 1/2. Fuel on one side/vacuum on the other side. I have 1/4" diameter fuel line to use with a 'T' connector. The one coming off the fuel filter looks to be about 3/8". I'll give it a shot and report my findings. Thank You!

Dear Rasmataz,
Yes you're correct.The repair manual says: 34 psi at idle and 43 psi when switching the vehicle a few seconds after the ignition switch is turned OFF then ON. Here are my findings at idle(rough of course, but slightly better).Can you examine the photo with the pressure on it and tell me what you think? Maybe you can make sense of it. I also performed a fuel pressure regulator test(per the manual). It reads: Start engine and read the indication of fuel pressure gauge as vacuum is changed. Fuel pressure should DECREASE as vacuum INCREASES. If results are unsatisfactory, replace fuel pressure regulator. Now my engine was surging at times during this test which should have made the vacuum signal stronger at one point as rpm's increased but it did not move from the word 'zero' on the hand pump gauge. Now I have a MityVac hand pump with the hose connected to the regulator with the hose plugged and at NO time did the vacuum gauge from the MityVac change. The fuel pressure did not move at any time either.

Dear Rasmataz,
I've attached a photo of the reading for the fuel pressure. I love this gauge!!! So easy to use and accurate.

The pressure only read at 43 psi and never 34 psi at idle like it states in the manual. Do I pull the vacuum line off of the fuel reg. to get the pressure to go down to 34 psi.? The injectors all read 8.5 ohms across the terminals(10-14 ohms @ 77*F is the spec.) All harnesses have battery voltage present and all injectors make the 'clicking' sound as the solenoid pulses on/off. So no problems there. Any other thoughts? Thank You!!!

Dear Rasmataz,
I will do these checks as you describe and report back to you. And yes. My gauge IS very pretty. Thanks for noticing. Thanks for your help!

Dear Rasmataz,
I did readings again for the sake of testing it again and I came up with these scenarios: fuel pressure regulator vacuum line attached; engine idling. Fuel pressure gauge still attached. The engine at idle pressure; hose attached reads at 36-38 psi, then the engine will rev up on it's own(surging)and the fuel pressure will drop to 34-35 psi, then the pressure will rise again to 38-40 psi; the engine will then stumble, as if to shut off then surge again, then stay at an rpm level of 1k or so then surge again and again. The surging happens about every 10 seconds or so. I haven't checked the fuel return line yet but this is what's happening now. Any thoughts!

Dear Rasmataz,
I've pulled off all of the rubber hoses that are in the fuel return line circuit and all of the hoses are clear of debris/foreign matter. Now, there are metal lines that I cannot test/check but nonetheless the other lines are totally clear. Now, when I did a second set of fuel pressure tests, DTC P0302 came up on the scanner(cyl. 2 misfire). I ran a spark test, pulled the cap and rotor and cleaned/inspected it. I even resistance checked the plug wires and they seemed alittle low on resistance. All appeared to be fine though. When I cleared the code after the testing, the MIL never came back. Maybe a false trigger. Do you still feel it's the pressure regulator?