Bad Brand New IAC !?!?!

[Three Dee]

Back in November, as part of a frustrating quest to figure out what is wrong with my i-spec '86 325, I replaced the idle air control valve because the old one was definitely dying. It seemed to address part of the problems I have been having, but recently the car has decided to die suddenly at lights (usually moments before it turns green, of course), or it tries to die while I am cruising down the road. A week or so ago I replaced the the throttle position sensor after first taking it apart and trying to clean it out, so this is not an issue. (Yes, I adjusted the TPS when I installed it.) The "sudden death" problem continued.

This morning I replaced the fuel filter, and once I got everything back in place I started it up and it started and ran just fine. Then I noticed that I had left the IAC unplugged. I plugged it back in, and about 30 seconds later the car died, and it was difficult to start. I unplugged it, and it started and runs fine, though the idle speed in Park is about 1400rpm.

My guess is that I bought a bad part, but I have a question:

I have been working on the assumption the car has electrical problems. Yesterday I checked the voltage at the IAC connector with the ignition off and a jumper where the main relay should be. I got 12.5 volts (battery voltage) on the center connector, and about 8 volts on the other terminals. Is this right?

[superj]

I have no idea on your voltage question but do you still have your old iac? if so, swap it in and see if anything changes. or find a local fellow e30 guy and ask to try his for a drive while you trouble shoot

[Three Dee]

I tried swapping in the old IAC and I either confirmed it is dead (the car just plain would not start) or that there is something weird still going on with the wiring. In the meantime, while the car is occasionally a tad difficult to start with the new IAC unplugged, it runs great. I'm going to go over wiring diagrams again today and see if I can figure out anything.

[superj]

until someone else posts, that sounds like a plan

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so you say I spec, so its got a 2.5? if its the regular 2.7, I can check the stuff you are asking when I get home, I have 3 86 325 in the driveway

[earthwormjim]

The ICV is controlled with a PWM signal, so you can't really measure the DC voltage accurately with a multi meter on all the terminals.

Best way to test if the ICV is at least electrically functional, is to put your key in the ignition, and turn it 1 click away from starting. Grasp the ICV with your hand, if it is working, it should be vibrating.

Now if it doesn't vibrate, that doesn't necessarily mean the fault is in the ICV itself. It instead may not be receiving a signal to regulate the idle.

Your real problem might actually be your throttle position switch again. Perhaps you have a leak, and it is getting gummed up with oil?

Also what brand ICV did you buy? I bought a new one on ebay from some no name brand, and it failed in a week. My OEM one worked fine again after a thorough cleaning.

You could hypothetically run without an ICV if you want, provided the weather in your area is pretty stable, and you don't change altitude much.

[superj]

that's true. back when I had a driveway full of e30s, I got bored and stripped one to see how light I could get it and it still run. part of the weight loss was wiring and non essential parts, which was the iac. I removed it and just set the throttle plate open where it idled how I wanted. worked great.

and the car ended up being on the top 10 lightest e30 list on e30tech, for ever. it might still be on there

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its still there, no 6


MOST ANOREXIC E30 Elite LIST:

1. killerbee......................................... .....................1851 lbs
'83 318 (318 shell, m20 turbo engine)
http://s71.photobucket.com/albums/i158/killerbeee/

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[Three Dee]

until someone else posts, that sounds like a plan


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so you say I spec, so its got a 2.5? if its the regular 2.7, I can check the stuff you are asking when I get home, I have 3 86 325 in the driveway

The original 2.7 kicked the bucket a few years ago and I had an '89 325i I had been mining for parts. It still had the engine, which seemed to be in pretty good shape, so I swapped engines and (of course) the engine management system and engine harness.

[Three Dee]

I bought the IAC from Parts Train, one of those budget parts suppliers on the net. Fortunately it has a one-year warranty. The TPS is just over a week old, and I got it from Rock Auto, and I've always had good luck with their parts.

Stable weather. Hmmm.... Yesterday here in my part of Kentucky it was in the forties most of the day. It dropped down to 15 last night and never got over 28 today. Back into the teens again tonight and into the forties tomorrow.

Does that qualify as "stable?"

[Three Dee]

The ICV is controlled with a PWM signal, so you can't really measure the DC voltage accurately with a multi meter on all the terminals.

Best way to test if the ICV is at least electrically functional, is to put your key in the ignition, and turn it 1 click away from starting. Grasp the ICV with your hand, if it is working, it should be vibrating.

Now if it doesn't vibrate, that doesn't necessarily mean the fault is in the ICV itself. It instead may not be receiving a signal to regulate the idle.

Your real problem might actually be your throttle position switch again. Perhaps you have a leak, and it is getting gummed up with oil?

Also what brand ICV did you buy? I bought a new one on ebay from some no name brand, and it failed in a week. My OEM one worked fine again after a thorough cleaning.

You could hypothetically run without an ICV if you want, provided the weather in your area is pretty stable, and you don't change altitude much.

I forgot to mention that the ICV/IAC is indeed vibrating like it should, though when I checked that yesterday (which was one of a number of times I have) it seemed weak. The old IAC also vibrates, and more loudly, but even after cleaning it wasn't operating correctly, which is why I decided to replace it. As for the new one, I started getting suspicious because while the engine would run okay if I left it unplugged, the engine would immediately die when I plugged it back in, unless I kept the revs up by holding the throttle open.

[earthwormjim]

I forgot to mention that the ICV/IAC is indeed vibrating like it should, though when I checked that yesterday (which was one of a number of times I have) it seemed weak. The old IAC also vibrates, and more loudly, but even after cleaning it wasn't operating correctly, which is why I decided to replace it. As for the new one, I started getting suspicious because while the engine would run okay if I left it unplugged, the engine would immediately die when I plugged it back in, unless I kept the revs up by holding the throttle open.

You honestly might just need to adjust your throttle body, when it's in the closed position.

To idle properly, the ICV needs to operate, and you need a small gap in the throttle body, so two sources of air for your engine. The ICV PWM has a limited range on the duty cycle when operating, so it can't actually go fully open, and stay open, that's why you need a gap in your throttle body when the butterfly is closed.

Over time your throttle body can get a layer of oil on it, closing the gap created at the factory. The screws which set the the gap can also move over 30 years too. It might just be, that the gap on your car now, is so small, that only with the ICV completely wide open, can your car idle.

I suggest marking the adjustment screw on the top of your throttle body as a reference for where you started. Unplug your ICV, and start the car. Adjust the closed position on your throttle body, until the car is idling at around 1000 RPM. Next, connect the ICV, and see if the car idles properly now. If it's constantly dying, increase the throttle body gap. If it is idling too high, close the gap.

[Three Dee]

I set it up today to run with no IAC at all. We'll see how that works. You may be right about the throttle plate. It was sticking shut at one point, so I adjusted it a little to keep that from happening. It may be I just needed to mess with it some more.

Of course, the batteries on the SI board are now dying, so the tach only wants to work on random occasions. I should never have bragged about the car passing the 333,333 mile mark.

[earthwormjim]

Fix the battery issue asap. If you don't have the lithium ion version, when those batteries go, they present a short to the SI board, which fries components and traces.