idles smooth when blower motor running

[xubuntu]

When the heater blower motor is not running the idle is a little rough......you turn the fan switch on high the idle smooths out. I suspect this is a grounding issue, power draw, or relay issue. I wanted to see if this is a known issue, before I begin troubleshooting. It's comically repeatable, and I would normally expect the opposite behavior. I have good charging regardless if the blower is running or not.

[black gold man]

Got AC

[rcb280z]

What year is the Z? Look at your climate control panel....what is the top left lever on? Is it on a/c or heat or...?

[SteveJ]

Got AC

Are you thinking it's the vacuum bottle for the AC at play here?

[Willoughby Z]

Or any non-stock changes to blower?

[Willoughby Z]

Are you thinking it's the vacuum bottle for the AC at play here?

That's what I'm thinking the posters are going for- A/C is on, compressor engages or is engaged, lever/switch "on" or not.

Magnetic solenoid would switch on, raising idle to compensate for compressor drag. The higher idle, in this case, is sounds better because the lower idle speed is probably a bit scratchy to begin with...

[xubuntu]

Thanks everyone for the ideas, and I apologize my signature didn’t post providing some basic information about the car.

1978 280z 4spd

Stock FI (new injectors, new pump, new regulator)

MSD 6A (stock Ignition Module removed) / Blaster Coil

CS-130 alternator upgrade

H4 HID's / MSA Type 3 Body Kit

Honda Blower Motor Upgrade

@everyone

This Z is recently resurrected, and I’m still working through some of the aging issues. The last 3 weeks, I have been using it as a part time commuter car to surface issues.

Currently the vacuum lines for the mag switches and vacuum actuator are disconnected because they were missing from PO’s and what tubing remained was degraded or misconnected. Since I have learned the hard lesson of vacuum leaks and lean condition with this FI, I’m incrementally testing all vacuum components and replacing tubing in stages. As it stands today the only (climate control) vac lines connected are

Manifold->vac canister->cabin controls

This minimal configuration was used to provide basic heat since the temp in GA dropped recently….prior to this all climate control vac lines were capped to troubleshoot a previous lean condition.

I don’t hear the AC clutch engage, and I suspect there is not enough charge in the system to permit the pressure switch to allow current to the clutch .

I will double check the AC clutch action this weekend.

I suspect the problem to be electrical related (ground/load/ailing relay), because the odd behavior is immediate (where I would suspect a vacuum related issue would have a slight delay).

With that being said, I do value field experience of forum users, and if this was a known quirk the best place to ask is here. I have had some interesting discoveries from PO’s “improvements” so at times on the surface it’s hard to discern what is a normal quirk, and what is unique to this Z.

@black gold man

It does have AC..looks factory

@rcb280z

Sorry for the missing info you should have it above…..normally it’s on bi-level or def….I only put it on bi-level because the coldest setting on heat is still too hot. Remember I leave the fan running when I drive to avoid the rough idle at stoplights

I should verify if the behavior is repeatable for all control positions I don’t normally use.

@SteveJ

I did leak test the canister before connecting it, and replaced the vac lines with copper tubing. I admit the copper tubing for vac lines is overkill, but I’ve had my fill of vacuum induced lean conditions with this FI.

@WilloughbyZ

I do have the Honda Blower motor upgrade in place.

I apologize for not mentioning that the AC components are largely disconnected (see above).

[grantf]

have someone switch the blower motor on while you watch the dash pot that increases idle and see if it moves.

[xubuntu]

@grantf

thanks for the advice, but it's disconnect at the moment

@everyone

I found out that running the headlights also induces a smoother idle.....so I feel confident that I'm dealing with an electrical conductivity issue, with either the ECM, the ignition system, for the Sense wire for the alternator. The alternator is charging at idle, but when high load accessories require the alternator to increase AMP's the engine electrical is benefiting from more available amps. In theory I believe the sense wire is the least likely problem, because if it had greater resistance due to corrosion it would register lower voltage to the alternator and it would begin over charging which isn't happening.

I'm going to measure current draws of the ECM, injectors, and ignition to see which is benefiting most to the available current.

It's also possible given the ECM is solid state and not digital, it can (in theory) be impacted by voltage swings. Fortunately if this is the case and not corrosion, I do have 12volt regulated power supplies I can add.