VG33 engine stalls when idle only when heater is on.

[DonutHands]

Any ideas? When the heater is turned on the engine RPM dips ever so slightly, and apparently when idle thats enough to make the engine stumble and shut off.

[FirstGenFreak]

Try disconnecting the wire to the air conditioning compressor, sounds like the compressor is bad- possibly sticky when engaged.

[DonutHands]

Well apparently its not just the heater (not running AC). So its raining here in Los Angeles, so it also cuts out when the headlights and windshield wipers are on at the same time. I see the RPM dip ever so slightly, then it cuts out.

[CamperDan]

I recommend having your Alternator and battery tested.

 

Chris

[FirstGenFreak]

What Dan said, Run a multi to the positive terminal on your alternator and see what its doing. 

[DonutHands]

Well, battery voltage and alternator voltage were just fine. Took it to a parts store and they tested the alternator, which said it had failing diodes or something like that. So figured what the hell, 27 year old alternator, sure lets replace it.

 

Just wrapped that up and yay! Same. Damn. Issue.

 

Any other thoughts?

[DonutHands]

Maybe my idle is just too  low?? Its a VG33 and when in gear its about 6-625. 

[Slartibartfast]

Did you have them test the new alternator? If the problem is the ripple from the alt getting worse under load and confusing the computer or something, then it should run without stalling if you disconnect the alternator. If it behaves the same whether the alt is connected or not, then it's not the alt.

 

Does the stalling happen from too many electrical loads, or just from these loads in particular? Will headlights + defroster do the same thing as headlights + blower?

 

My first thought was that you've got a weak connection somewhere that's dropping voltage under load. I looked up the wiring for the headlights, blower motor, wiper motor, and engine computer to see what they had in common, and the answer is not much. The blower and wiper do share the same fuse and ground points, but the headlights and computer/sensors do not. If the starter's still working, that rules out loose battery terminals. If the connection where the negative battery terminal bolts to the fender is compromised, that would bottleneck everything in the body harness, without impacting the starter. It's a long shot, but if you run out of things to check, make sure that connection is clean and tight.

 

Annoyingly, the FSM doesn't spec an idle speed in gear. 750 +/-50 in neutral, 700 if the TPS is unplugged. 800+ if the aircon is on. I don't remember offhand what the warm idle in gear is on my WD21, but 600-625 sounds about right.