2003 QX4 surging

[whitesnstripes]

My 2003 Infiniti QX4 died with a DTC P0507. Before I read everything I could on the internet I prematurely replaced the MAF, Throttle Position Sensor, fuel filter, plugs and pcv valve.. I have since replaced the Idle Air Control Valve and had the ECU rebuilt. After attempting an Idle Relearn with no success I decided to purchase a Consult 3. I've successfully done the Idle Relearn but can't get past the surging and unable to accelerate above 1800 rpm's.

I'm guilty of "shotgunning" some of this and quickly running out of money. I don't currently have any DTC's and have driven it for hours accelerating patiently. But this can't be my only solution?

Help?

[Towncivilian]

Another potential cause is intake air leaks; you've already ruled out IACV (and hopefully its circuit), ECM, and the PCV system.

Check for intake air leaks first (spray brake cleaner or starting fluid around air intake plumbing to see if engine revolutions increase momentarily).

Try following the diagnostic procedure afresh - see page EC-462 of the factory service manual.

When you replaced the PCV valve, did you notice any missing screws on the power valve butterfly plates? You should have applied red threadlocker to them while you had everything apart, since there is a potential issue where the screws can back out and get ingested by the engine.

How many miles are on your QX4? Does it consume any oil?

Welcome to NICO. You've spent a lot of money unfortunately, especially for that CONSULT-III. Did you use OEM parts for all your part replacements?

[whitesnstripes]

I need to test the circuit today. I replaced the IACV first and drove the car for almost a thousand miles while it had the symptoms of erratic idle in neutral. Finally decided I couldn't live with that and sent the ECU off to be rebuilt. Once I reinstalled the ECU, it ran for about ten minutes and fried the ECU again. The rebuilder said it was because the IACV was bad from having ran with the bad ECU during the thousand miles. I sent the ECU off again and bought an aftermarket IACV from Autozone for $369. The plug for the IACV was overheated and had evidence of melting, so I certainly need to test those wires back to the ECU today.

As for the intake, I've sprayed the engine several times "hoping" to find a leak to no avail. I'm completely unfamiliar with the power valve and will do some reading up on it today. The car has around 100K miles on it and does burn about 2 qts of oil in 3k mile intervals. Not sure how relevant it is, but I did run a power balance test on it and the cylinders were between 128 and 131.

I didn't use OEM parts because they are unfortunately unaffordable, but a non running automobile is also, unaffordable! I did test them with the ohmeter before installing them and seemed within tolerances.

Thanks for your input!

[Towncivilian]

2 quarts in 3k miles is almost unacceptable. Most manufacturers deem "acceptable" oil consumption as 1 quart per 1000 miles, but even 2 per 3 is too excessive in my opinion. Power valve screw(s) ingested could be a likely cause of your oil consumption. Have you owned this vehicle since new? If so, have you kept up with oil changes? You need to check those power valve screws. See this DIY guide.

Is the IACV on your 2003 QX4 not built in to the throttle body, since it is drive-by-wire and not a mechanical throttle body?

Try idle air volume relearning on page EC-69 of the FSM if you haven't yet.

Your compression values are below minimum (range is 142 minimum, nominal is 185, max allowable difference between cylinders is 10; all units PSI). Did you follow the compression test steps on page EM-14 of the FSM?

[whitesnstripes]

I've only owned it for 18 months and put about 30,000 miles on it. It was burning oil prior to me purchasing it. I'll plan on checking the power valve screws and compression test this weekend. Can I reuse the gaskets?

I've done the idle relearn many times. It shows CMPLT but misses and backfires when I try to press the accelerator above 1500 rpm's. When I first start the car cold, it doesn't backfire and will accelerate at idle up to 3000 rpm's steadily. But after it warms up, back to misfiring. It even feels like the transmission slips momentarily sometimes while I'm driving it?

I performed all of the steps for EC-462 except 3. I need to find a method of probing the ECM terminal without piercing the wire. Otherwise everything else tested fine.

I ran some diagnostics and wanted to see if anything stood out to you. The IACV 6 Step was a concern, shouldn't it be around 14?.

Eng Speed 750 rpm
Timing 15 BTDC
IACV 6 Step
MAS A/F SE-B1 1.37v
B/Fuel Schdl 2.5 ms
POS Count 180
AF ALPHA - B1 110%
AF ALPHA - B2 110%
coolant temp 190 F
HO2S1 - B1 .05 v
HO2S1 - B2 .01 v
HO2S2 - B1 .25v
HO2S2 - B2 .25v
Batt Volt 13.9 v
INJ Pulse - B1 2.5 ms
INJ Pulse - B2 2.5 ms
MAF 3.03 g/s
IACV-AAC/V 6 step
INT/V TIM B1 0 CA
INT/V TIM B2 1 CA
HO2S1 MNTR B1 LEAN
HO2S1 MNTR B2 LEAN
HO2S1 HTR B1 ON
HO2S1 HTR B2 ON
HO2S2 HTR B1 OFF
HO2S2 HTR B2 OFF
Closed Thrt P/SW ON
P/N POS SW ON
PW/ST Signal OFF
LOAD Signal OFF
SWL CON VC SW ON
SWL CON S/V OFF
VIAS S/V -1 OFF
VC/V Bypass/V OFF

Thank you so much for taking the time to help me!

Scottie

[whitesnstripes]

I was wrong on the power balance test. I'm not sure if the results are psi or not, but the results are below.

1. 275
2. 273
3. 281
4. 281
5. 285
6. 280

[Towncivilian]

Page EM-14 has the compression tolerances.

Page GI-22 has instructions on backprobing connectors (if these instructions are useless let me know).

Check the resistance of the engine coolant temperature sensor - reference values are on EC-225.

You can't re-use the gaskets. You'll need the top three gaskets since you shouldn't need to remove the lower intake manifold - just be careful when removing and securing the power valve screws. The butterfly valves require some considerable force to access, so it's unlikely you'll drop a screw in. However, without the LIM off it may be difficult to access the power valve screws. I'm small and was able to crouch atop the radiator core support, but this may be implausible for you.

I'm not at home so I'll write more later. Good luck!

[Towncivilian]

Your QX4 has an electrical throttle body, so the part number for the throttle body gasket is incorrect as it's for the older mechanical TB. I don't have the correct part number for that at the moment, please provide your VIN so I can look it up.

Use red threadlocker for the power valve screws, as these screws should never need to be removed again.

If you find any missing, that is bad and engine damage is a very possible result of that. It may be causing your oil consumption.

[whitesnstripes]

I don't have the vin available but hoping the data plate and pics will help in the meantime?

[Towncivilian]

Do you have a larger picture of the certification plate? It's microscopic and I can't make out some of the VIN letters.

[whitesnstripes]

Nissan Motor Co.
Type JLR50
Chassis No. (VIN) JNRDDO9X63W252313
Model JLJULVAR5OEUA-G---
Engine VQ35(DE) 3498

[Towncivilian]

Sorry for the very late reply. Your correct VIN is JNRDR09X63W252313, you made a couple typos.

FAST says that all the part numbers are identical to those posted in the DIY guide. My apologies again, I seem to have misremembered and thought that VQ35DEs with electrical throttle bodies had different gaskets. Apparently, this is not the case. Regardless, be sure to provide your VIN when you order the parts to ensure that they are the correct gaskets.