Obnoxious idle problem with 2Vi -- sick and fed up.

If anyone here can help, I would sure appreciate it.

In a nutshell, when the car is warm/hot, the voltage drops progressively to around 12, and the idle gets low and sickly, to the point it is barely idling at all, and the exhaust gets very strong with the smell of being rich, to the point my eyes burn from just being near it.

Again, it only does it when it is warm. From beginning with a healthy idle, the problem starts with a slight change in the exhaust note rhythm, as if a switch has been flicked somewhere, and the idle slowly begins to get progressively worse, until a few minutes later I'm choking from the fumes and the engine is hobbling along at a minimum idle, about to stall out. As the idle is dropping, so is the voltage.

It drives absolutely fine when it does this, but then when I come to a stop (traffic light, etc.), it's barely idling. Problem only manifests itself at idle; car drives fine otherwise.

What are your suggestions?










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Okay, that's the short version. If you like to read, continue below:


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HISTORY OF THIS PROBLEM
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My history of trying to fix this problem is long. It started with my replacing the voltage regulator, but the one Superformance sent me was the wrong piece, and it burned out one of my Digiplexes (ba$tards). I'm not sure whether it addressed the idle issue, anyway (I don't remember for sure, but I don't think it did).

So I went back to the old voltage regulator and bought two nearly-new Digiplexes out of a perfect-running 11k mile car that had been hit. Car seemed to run better for a short time, but problem came back.

I also grounded the digiplexes externally, as recommended, and tested 0 ohms from digi body to car body, as well as in the plug.

I replaced all three reference sensors.

Tested the coils and all ignition system wiring.

Replaced spark plugs, extenders, and wires (it needed it anyway).

Car has Birdman fuse blocks. A couple of things were done incorrectly in it by PO. His mechanic fixed a couple of his screw ups; I fixed a couple more. Wiring screw ups were for the interior blower motors and headlamps/turn indicators; no direct wiring screw ups related to fuel pump circuit. But the idle issue did start in the PO's ownership, so I wouldn't be surprised if he did something to screw it up and cause the problem.

I felt that the fuel pump wire going from the main junction on the relay board to the fuse was getting hot at the spade (it was a little burned), so I replaced it.

The fuel pump relay does get hot in use, but I think that's normal, right? I'm including fuseblock/fuel pump circuit stuff because of potential for it to be a resistance point causing a voltage drop throughout the car. (?)

I also disconnected the high idle warmup circuit and plumbed closed the vacuum line there. The idle problem was there before and after this change.


At this point, here is some of my "thinking out loud" about what could be happening:

Perhaps something electrical is getting hot and causing a voltage drop at idle, and the low voltage is the cause of the poor running (I've been told that Digiplex system is sensitive to voltage inputs). The 'something electrical getting hot' could be a case of high resistance reducing voltage, or it could be something switching on or off or shorting due to temperature. Possible culprits I'm thinking of are voltage regulator (but that didn't seem to do it last time, IIRC), or some other part of the alternator? Something in the fuse/relay panel? And/or is there a temperature sensor for the CIS system that controls the air flow or mixture?-(but how could this affect voltage...)


I'm open to your suggestions. I feel pretty confident that there are no issues with the ignition system (and it does run fantastic). I'm looking for clues or suggestions particularly related to the car's electrical system and/or fuel injection.


Thanks for reading,

Tony

 

I agree about not messing with A/F adjustment yet, as the car runs perfectly when it's not doing it, and has a long history of passing emissions tests, and no adjustments have been made in the past.

Replaced all vacuum hoses. Spent a long time looking for vacuum leaks. Pretty certain there are none. Even if, those don't explain the voltage.

Brand new Interstate battery. No battery drain issues, normal voltage when turned off.

When car is cold, and when it's not doing the problem, the voltage is 13.5-14 all the time, any engine speed (don't remember details, as I last checked it last fall, but there was nothing out of the ordinary and I've checked it on several occasions -- enough to remember this much.) Will check again in the next day or so to get exact numbers.

At idle, let's say it's at 13.6 to start. If I let it sit there, it gets nice and warm, and at some point there is a slight change in the rhythm of the idle, and then the voltage starts to drop, in sync with the idle getting weaker/exhaust getting richer. Over the course of 2-4 minutes (never timed it exactly), it will drop to the point where the car is barely idling, and the voltage will be below 12. Will go as low as low 11s. I don't think it ever dipped into the 10s. Measured at battery, fuse blocks, coils, several other places, all the same throughout the car. At the same time, the idle will be similar to if you were to close the large idle air screw on the plenum all the way, only lower. To keep the car idling, I actually back the screw out a bit; the result is an idle of about 1200-1250 when it's behaving normally. In other words, if I set my idle to 900-1000 when the problem is not happening, then when the problem does happen, it'll pretty much stall out.

But while it's doing the poor idle thing, if I step on the gas, it's fine as quickly as it takes to clear the combustion chambers out a bit. It runs/drives fine whether driving around town or on the freeway; but when I come to a traffic light or such, it's in poor idle mode already. Voltage definitely steps up when driving, because lights get brighter when I step on the gas pedal. I don't have exact numbers, but I'm going to go and wire a cigarette lighter plug so I have something to hook my voltmeter up to while driving. But the voltage definitely increases while driving. I'll have hard numbers in a day or two.


For the fuel system suggestions -- I'm not ruling those out yet, but I want to first have an explanation for the voltage drop, because I can't think of a CIS issue that can reduce the voltage throughout the whole car. But I'm very open to ideas/explanations/rationale!


Thanks for your help and continued suggestions,

Tony