1990 Maxima, VG30E: rough idle, manual EGR smooths out?

[slipnfall]

Hi folks,

I just bought this car, 160k on the clock, and this series of engines are all new to me. I'm plenty good with the KA series of engines, and I think a lot of the same principals apply here also.

Anyways, the car has a pretty rough idle, enough to vibrate the engine, but not severe like a crossed plug wire. When I manually actuate the EGR valve, it smooths down to almost a pur! This means by ingesting more air, the idle is smoothing out: this implies the mixture is over-rich? No smoke, but the exhaust does smell of fuel. From the vac diagram this should be correct: apply vac. to direct gas into the intake mani.

I was under the impression the EGR should *not* be active at idle, but will if RPM is raised(no load). SO, perhaps a leaking injector? The head temp sensor was disconnected, so I tested that and reconnected (after cleaning and "re-springing" the female terminals for a better fit).

I've squeezed the IACV bypass hose, engine speed decreased, as I would think it should(?).

I let the car guzzle about a 1/2 can of seafoam, and it seemed to help a little, but still a bad idle. Lack of power also.

I know this is all really vauge, however, I'm not used to diagnosing an engine without a computer interface!! I know enough though to tell it isn't running right.

BTW: can anyone tell me, can the "checker box interface" connector be used to put the ECM into the 5 different modes? Is it worth messing with over the potentiometer on the ECU itself?

Thanks for reading.Jamie

[slipnfall]

Well I've just been pulling off the intake parts slowly cleaning and testing everything. Turns out the 'power valve' is bad: it won't hold air/vacuum. So definate leak there.

Is this similar to the KA engines with the butterflys? It essentially shortens the intake runner length at low RPM to increase torque output(?). Does the ECU do any fuel enrichment or anything when it's activated? I presume that in steady state the valves are open: I'd like to consider just bypassing it if there aren't any ill effects.

Thanks,Slip

[slipnfall]

I know I know, I'm talking to myself here, but who knows, maybe this will help someone else.

I confirmed how the EGR operates: (this is a federal model BTW, so no EGR-BPT). With no control signal on the EGR solenoid, vacuum flows from the intake manifold, to the vac hard-lines, and into a port on the solenoid. At rest this vacuum is allowed to pass through and onto the EGR, which allows gas to recirc into the intake.

At idle the EGR was not operating, and I'm still unsure if this is correct or not. Anyways there were some bad vac lines: replaced those. I also found by manually activating the solenoid, the vac intake was not being shut off completely, allowing it to vent to atmo: so if/when the ECU engaged this solenoid, it caused a vacuum leak (actually there was a vac leak in both conditions).

I also figured out the operation of the power valve: vacuum is supplied to the reservoir via a one-way valve. Once into the resov. it passes to the power-valve solenoid. When the ECU activates the solenoid, the vacuum is immediately supplied to the power valve actuator, opening the butterflies. At the same time this 'surge' in vacuum causes the one-way inline valve to close, and allowing the reservoir to supply the 'pulse' of vacuum needed. When the pressure has equalized, the valve re-opens to enable a solid vacuum supply from the manifold.

So does this power valve actuator just require so much vacuum that it could potentially cause a drop in vacuum in the intake mani? I presume this is why the reservoir is there.

Anyone who has any insite or corrections, *please* chime in!