Fault Code: Battery Voltage/DME Main Relay

[mzender]

So still have not figured out what the problem is. Although I have a couple more symptoms whether they are directly related or not. When the car is completely cold on start up it only brings the idle up to around 1,000 rpm untill I touch the throttle then it picks up to 1,500 or higher as it should untill it starts to warm up. Anoter thing it does related to the cold start up is after it picks the idle up to where it's supposed to be when cold, soon as I start driving(backing out of my driveway) it cuts out suddenly but only for a split second and not harsh enough to come close to causing it to stall, just bad enough to feel and hear it do it. And it will only do that once at the same point everytime, and only when it's completely cold at start up, like it sitting over night and the first time it's run all day sort of deal.

Now the other thing I noticed it do the other day is when I was driving in town the other night is the motor sounded as if it was under a sudden load and all lights dimmed suddenly but progressively returned to normal shortly after. At the moment this happened I assumed it was just my fan kicking on(I deleted the mech. fan and installed an electric fan in it's place), but after thinking about it, this has never happened any other time the fan has kicked on. I can't tell for sure when the fan kicks on because the fan I installed is very quiet and I only every notice it come on and off if I'm watching the digital temp gauge I installed in the glove box to monitor it, or I'm watching it with the hood open. In testing to make sure it was turning on and off when I put the fan in the first few days i had never noticed it dim the lights at all when driving at night.

Would this likely be caused by my voltage regulator being on the fritz basically doing as it pleases? Or when they normally go bad do they just go out completely? Could my DME corrosion be causing this also? Any new ideas would be greatly appreciated, thanks.

[mzender]

So my predictions are going to be one of these 3 problems being my answer. None of which I have the spare cash for right now to replace. A. Throttle Position Sensor B. Computer is fried/corroded to the point of malfunction C. o2 sensor issue.

Anyone know where to pick these 3 things up cheap? The o2 I can pick up off eBay relatively cheap if I figure out that's the problem. DME is a 402? (or 405?) whichever is the brown label. I'm pretty sure it's 402. And the TPS I've done no reall homework on so far, I just know they're not cheap at oem prices.

When I get the chance I'll pull my car in the shop and test the TPS and o2 via the Bentley manual.

My theories on those things being wrong are based on a symptom observation I made when driving my car that is really going to be hard to explain in text. Basically, the most noticable part of this symptom, which I mentioned a little on this early in the thread.. anyways, under heavy throttle it feels as if it's losing power then picking power back up then losing and on and on in a constant cycle(searching I believe is the term I used earlier on). So anyways, the observation I noticed when it's doing this, is when watching the MPG sweep gauge under the tach while it's cutting back and forth relatively fact on power the needle is sweeping back and forth at the same exact rate as the power changes. As if it is confused and not getting a signal of where it's supposed to be running so it's cycling through it's range back and forth trying to find what it's supposed to be running at. I don't remember for sure but I think when the power seems to pick up where it's supposed to be the MPG needle moves toward zero, then when it loses power the needle moves toward 40. Obviously it doesn't move all the way back and forth, but I'd say it swings back and forth between 5ish-20ish MPG on the gauge. So it moves quite a bit.

So anyone with similar experience or any incite, please pitch in.

[mzender]

Successfully got the stomp code test to work. It confirmed with code 1231. Anyone know anyone with a good 92 DME 402 I could borrow to test on good faith to see if my DME is just fried due to water damage? I can't afford to go out and buy one just to see if that is actually what is wrong. Thanks

Edit, I just picked up a DME off ebay cheap so I'll try that and see if it's my problem. I'll post back with the results for anyone who may be following this thread.

[eurokevin]

sounds like your dme. i never had a starting issue when mine got wet, instead it would feel like it would bog under load.when i let off of the throttle and then eased it to the floor, it drove fine until it died a mile down the road lol. cooked the dme in the oven and i was lucky enough for it to work again.

[mzender]

So I got the new DME in the mail and threw it in quick before work yesterday, it was my problem the whole time. No more check engine light and it runs smoothly throughout the RPM without any dead spots. The cruise control still does the suddenly jerky RPM change at random though, thinking it might have something to do with the recall on it. But figured I'd let whomever know that's following this thread or has similar issues that this is what fixed mine.

[fun2drive]

Fantastic. Not one of BMWs best designs for the vent area and drains but now you have a ride that is reliable.
I don't have a lot of experience repairing DMEs but since they are so cheap for your car glad it all worked out.
Also the way the voltage regulator works is once started it will slowly ramp up to around 14.5VDC from static starting voltage then adjust down.
Nice job....

[e36mikee]

^^ damn that must be my problem, weird thing for my 92 325 is that the code used to stay on at all times, then i tested alt which was bad and the battery was also ruined because of it, so i got both those, code went away. then it started coming on randomly on and off. my dme has been soaked before, but everything returned to normal, this whole thing only happened for me after i used my friends m3 cigarette lighter, and it killed my battery. but thats probably the issue, im getting a new car anyway, but maybe i can do this an smog it in the meantime.

[Rodrig970]

Anyone delt with wiring on these? Gotta be someone who can help me?

I have a similar problem but i would suggest getting a wiring diagram and just trace the right color wire from the pcm to its corresponding location which would show you the the color of that wire at the other end. Thats what i did