SR Blacktop Idle Troubleshooting

[jscherf92]

I need to format this a bit to get the information across without writing an essay so here goes...

Engine Diagnostics:
-Consult cable with ECUTalk, Conzult, NDS
-Zeitronix Wideband at test pipe
-Timing light
-Volt meter

Current Problems:
-High idle (sits around 1500 when warmed up)
-Timing off (not sure exactly but suspected)
-Some hesitation on acceleration

Things i've messed with:
-Set TPS voltage range .35v closed - 4.0v WOT
-Cleaned MAF, slightly high voltage readings before
-Replaced spark plugs with NGK and gapped to spec, old ones were burnt
-Checked mechanical timing chain/cams
-Attempted to lock timing mode with Conzult and set with timing light and CAS, idle was too high (1400-1500) and IACV doesn't want to adjust
-O2 sensor reading was wildly fluctuating with idle speed between 1200 and 2000, unplugged and idle settled down to 1400ish
-wideband reads between 14 and 16

Also getting a knock sensor error code.

My understanding is that letting the engine warm up, using conzult to lock timing mode, adjusting the IACV to lower idle speed, and then setting timing with a light and CAS is what I should be doing, but it'd be great if anyone recognized any other problems while im messing with it.

Please ask any questions that would help clear this up and ill answer back as quick as I can. Ill update with anything I find or test as I go.

[jakemkz]

Hello,
Have you tried following the idle adjustment procedure outlined in the FSM? It is quite specific and has several steps that must be done in the correct order. Also is there any noticeable difference in performance when the engine is cold vs warmed up? If the coolant temperature sensor connected to the ECU is faulty the ECU sees the engine as always cold and injects much more fuel than it should (with a cold engine fuel evaporation is poor so excess fuel is injected). Since the idle setup is supposed to be done with the engine warm this could explain why the consult system is locking you out.

If you are getting a knock sensor error code the ECU will retard spark timing to a safe level that will not induce knock, even on regular gas. This is probably around 5 deg, but the amount of retard may vary throughout the map, I haven't measured it personally. I highly recommend installing a new Nissan knock sensor.

If none of the procedures in the FSM work out (see S14 FSM pages EC-35 to EC-40 and the trouble diagnosis section that follows) the throttle plate stop screw may have been adjusted too far in, backing it out could help. Good luck.

[jscherf92]

Alright first to last, and thanks for the quick reply...

-I'll get my hands on an SR FSM but its spelled out pretty thoroughly on different forums and sites
-Idle is about the same, maybe a bit smoother when warm but the sensor is reading and functioning as it should.
-I'm not getting "locked out" of the consult system, i'm using it to engage "timing mode" instead of doing the magic rev to 2k for xx minutes and rev xx times while patting your head and rubbing your stomach which I couldn't figure out.
-I've ordered a new knock sensor and wire sub-harness. Apparently mine had de-pinned itself and my repair efforts failed. if nothing else Ill have a second known-good spare.
-Again, ill get my hands on a blacktop SR specific FSM but the throttle position sensor is reading in spec after adjustment.

[jakemkz]

OK, thanks for the clarification. Until the knock sensor is replaced I don't think you will have much success with the idle calibration, but you should be able to find the cause of the high idle. When you say the O2 sensor reading was fluctuating do you mean it was alternating between rich/lean quickly? If so this is the correct behavior but was the engine speed also hunting while this was occurring? (please excuse me, I am having trouble parsing exactly what is meant by some of your original descriptions.) It seems like you have done quite a bit of troubleshooting so this may have simply been too basic for you to mention, but have you checked for any vac. leaks? If there aren't any vacuum leaks you could try disconnecting the FICD solenoid and AAC valve, this should cause idle to drop. If it doesn't drop to below 800 I would try backing off the throttle stop screw until the idle is around 700, then plug the IACV back in. Best regards,
-JM

[jscherf92]

O2 was going from rich to lean quickly so I guess I shouldn't worry about that. It was speed hunting at the time, but on another try it was doing that whether or not the o2 sensor was plugged in.

I have looked around for vac leaks but you're right about that being a basic issue, ill give it another thorough inspection just to be sure. When you say disconnect the FICD (IACV?) / AAC do you mean removing the hose that is diverting air from the intercooler pipe or the electrical connection? Ill experiment a bit more with the idle air solenoid and throttle body to see what I can get. Thanks again for your help, sometimes I just need a little brainstorming to come up with ideas I'm too frustrated to think up.

[jakemkz]

Hi, I meant the electrical connection the IACV is composed of two parts, one is the FICD (fast idle control device) which is a solenoid that puts the engine into the "high idle" state by opening a small passage, the other is the AAC (auxiliary air control) valve, this is the valve that is modulated to control the idle RPM. If you disconnect the electrical connection I believe both valves will close (although AAC valve has a thermostatic valve which may remain slightly open). If the IACV is not active and idle is still high there must be some other location where excess air is entering the manifold, either that or the IACV is stuck open. Good luck, please let me know if you figure things out, I'm interested in hearing what the solution ends up being.

[jscherf92]

Ah that makes sense thank you for all the clarification. Ill report back tomorrow after work when I get some time to keep working on it.

[jscherf92]

Quick update. Pressurized from the intercooler piping through to the intake manifold and found a few small leaks, swapped out a few loose vacuum lines, found another leak under the 2nd runner between the intake manifold and the head, threw on a new intake manifold gasket (only one, its a knockoff greddy style), and im letting the permatex cure before adding pressure.

[jakemkz]

That sounds like great progress, finding and sealing these leaks is definitely a step in the right direction.