S13 SR idle problem

[WilloW]

Hi everyone, today I replaced my broken oxygen sensor (can hear it rattling when shaken) as well as my spark plugs. Prior to this the car ran just fine without any of the current symptoms. After I changed out the oxygen sensor and spark plugs and saw the symptoms, I tried to set the idle by warming it up and disconnecting the TPS then set idle.

Currently the symptoms includes:
1. Idle is moving between 850-1100. Most of the time it is at 8500, but once in a while it revs up to ~ 1100.
2. Between the above range it is also breaking up and I can feel/see the vibration of the engine. Basically sounds like it hiccuping.

I replaced the oxygen sensor with a skinny Nissan sensor. As for the spark plugs, I'm currently using those V-power BKR7E gapped at 0.28. The last time I checked they TPS voltage it was at 0.45 at idle, I didn't think to check the voltage at WOT.

Thank you in advance for any input, I want to sort this out soon before school starts again.

[Def]

So it's not a rhythmic surge in idle speed? Then it's probably not IACV related.

Have you checked your ignition timing lately?

Does it make any difference if you drive the car for say 20 mins then let it idle for a while?

[pedroramosjr]

Have you tried putting your ecu into diag mode to make sure that the O2 sensor is functioning?

[WilloW]

Jacob, it doesn't do that rpm hunting thing. Sometime it would be dead on at 850, 30 minutes later it would climb up to 1100 when I stop at the light, 15 minutes later it would be at 850 and doing the hiccup thing, then later it would later slowly go down to 850 from 1100. I'm starting to think that I have a bad TPS. I've noticed that sometime when I'm at cruising speed and is not modulating the throttle, the car would slightly "push" a bit as if I'm slightly depressing the pedal.

Pedroramosjr, last I checked timing with a light it was at 15* and the ECU gave me a code 55.

I'm going to consult the FSM tonight and start checking the oxygen sensor and TPS's voltage tomorrow. Thank you guys for chiming in.

[Def]

I had some crap blocking the water feed to my IACV after doing a flush(previous owner in Japan used the orange Dex-whatever coolant.. thanks buddy), and it would act like what you are describing. It'd cool down while cruising, so it'd go to a half "cold idle," then it'd heat up while at idle and drop back down(slowly).

Try unplugging the IACV and see what happens. I bet it idles fine when cold, then it'll slowly start dipping down as the car heats up and the IACV wax starts melting a bit.

[WilloW]

I had some crap blocking the water feed to my IACV after doing a flush(previous owner in Japan used the orange Dex-whatever coolant.. thanks buddy), and it would act like what you are describing. It'd cool down while cruising, so it'd go to a half "cold idle," then it'd heat up while at idle and drop back down(slowly).

Try unplugging the IACV and see what happens. I bet it idles fine when cold, then it'll slowly start dipping down as the car heats up and the IACV wax starts melting a bit.

I can't remember if I had orangy crap in the old coolant. How did you ended up fixing the problem?

I would hate to try to get to the IACV and have the intake manifold disassembled and all that jazz .

[Def]

I ended up just plugging the IACV lines and running back the lines going to the throttle body. Worked just fine after that.

[WilloW]

I ended up just plugging the IACV lines and running back the lines going to the throttle body. Worked just fine after that.

So you're basically running without the IACV?

This afternoon I totally forgot to tried what what you said with the IACV. However, as I was adjusting the idle there was something weird. I had the car warmed up to operating temperature and it did it usual hiccup and stutter at idle. As soon as I unplugged the TPS to adjust the idle, the idle was rock solid at where I adjusted it to and stayed there as long as I didn't plug back the TPS.

I rechecked the voltage of the TPS at key "ON" and it was at 0.44, at WOT it shows 4.21. Should it be at 4.00 at WOT?

Does this mean that either the TPS or the IACV is fubar?

[Matt93SE]

1. The strange TPS voltage could also mean you have a funky ground on your engine or TPS or IAcV or something like that. It can't hurt anything to try this.... pull all your ground wires off the block and chassis, clean the connectors and the mating surface, then apply a little dielectrics grease (or just grease if that's all you have) and see if that does anything.

2. Have you modified the engine much to need more air at idle? i.e. when I went to high compression pistons and ported the heads in my Maxima, the engine wanted to flow more air at idle than the IACV could feed it. I had to take the IACV off and drill the tiny hole out just a bit larger and the IACV worked properly again.

2a. Does your IACV make any noise when it's plugged in at idle? The IACV on my VE30DE engine will 'hum' at idle as it's pulsing open and closed.

Disclaimer: I dunno sheit about SRs- only worked on one SR20DET- but the hunting and stumble at idle is pretty typical of Nissans... IACVs are finicky about all kinds of crap. could be the O2, could be TPS, could be anything.

[Def]

Just made me think, have you ever messed with your IACV set screw? It could be open too much so even at 0 duty cycle the idle will creep up under certain conditions.

Might be worth closing it down a tad and seeing what affect that has.

Also, do you have a BOV vented to the atmosphere? I've seen all sorts of weird idle behavior when there are BOVs vented and they didn't seal up well etc. at idle and were blowing out a bit of air.

[WilloW]

"Matt93SE", I will definitely try the ground and grease thing. The engine is basically stock with a Walbro, front mount and some other miscellaneous. At idle the damn exhaust is too loud for me to hear anything, the only thing I hear are the injectors clicking.

Jacob, I played with the adjustment screw before when I finished my swap. Today, I try closing it to the point where it was almost all the way down and the engine was struggling to stay alive then adjusted back up to 850. My BOV is ricirculated the whole time.

The thing that pissed me off is that this starts when I replaced the oxygen sensor and the plugs.

[WilloW]

Holy hell, this is embarrassing. After I did all these crazy madness crap such as cleaning the IACV, triple checking voltage on the sensors (O2, TPS, IACV), checking for vacuum leaks. I had neglected to check the oxygen sensor pin-out. Originally my car had the "fat" O2, I accidentally ordered the "skinny" O2 but had the adapter for the turbo elbow. I figured it should be a plug and play deal but it wasn't. The "skinny" O2 has the signal wire at a different pin vs the "fat" O2. It took 30 second for me to swap the pins and the car now idle perfectly with no miss, hiccups, hunting, or any of the crap that I have described above.

Thank you all very much for all your inputs.

[Def]

Easy fixes are the best fixes!

[Matt93SE]

Good catch!