325is surging idle?

[Atara]

So, I just bought a 325is yesterday (automatic) from a user here and it was running perfectly. Drove it around for maybe 40-50 miles and came home and was just poking around looking at everything and took off the fuse box cover, when I did this 2 fuses came out. I was able to grab one of them but one fell into the engine bay somewhere in the direction of the arrow (picture below) and I was unable to find it. I put the fuse I had found back in and drove around a little bit and it seemed fine. This morning I went over to starbucks and while I was waiting the surging idle issue started. I figured it was an issue with the missing fuse so I checked all the fuses against this list: http://www.r3vlimited.com/board/showthread.php?t=60297 and replaced every one that sounded like it had something to do with my problem. I did this in the parking lot of the auto parts store that I bought the fuses at. When I was pulling out of the parking lot it stalled, started it up again and drove a tiny bit, stalled again. This happened a few times until I got it running just enough to get home. I took a short video with my camera and a flashlight to show the issue. I'm also posting a picture of the fuse box as it currently is.

[Atara]

Also, when that was happening (in the video), if I shifted into drive/reverse the car would stall. What I just did was start the car, get immediately into drive and started going. Once the car is moving it's fine. I drove it around my neighborhood for a while, took it on the freeway, drove it around some more and came back home. After I got back I sat there for about 10 minutes idling and didn't have the issue. Going to go back out in an hour or 2 and see what's happening.

[u3b3rg33k]

Do you have a 153 DME? if so, get a 173.

[Atara]

I have no idea what that means. New to e30's and cars in general. I just went out again and it did the surging thing once when I started it up and sat there for a while. After I got back from driving for 20-30 mins or so it had no issues, just sat there purring. It seems like when the car is heated up its fine.

[u3b3rg33k]

In the glovebox, above the plastic separator, lies the DME (aka ECU).

For example, that's a 153 DME. runs motronic 1.1. You want a 173, which runs motronic 1.3. Newer board, newer software, better idle control, and stomp codes.

I noticed a huge behavioral change in idle control when switching from a 153 to a 173. I would have surging idle issues that would develop with the A/C running, (almost stalling, rev up, almost stalling...) and the occasional almost stall when coming to a stop while the compressor kicked in while I stepped on the clutch. The 173 solved those problems.

[Atara]

Would that be something that's easy to swap in if I pick one up? I've got the e30 Bentley manual, I'll see if that's in there!

[u3b3rg33k]

Very easy. if you can hook up a parallel printer, you can swap a DME.

If you're the type that breaks off a VGA port while trying to push a parallel cable into it, don't touch it.

[Atara]

Sounds good! I build/repair computers all the time so that shouldn't be an issue, now to find one. How much do they usually go for?

[u3b3rg33k]

I usually see them for $60-70. Check the FS section.

[Atara]

Will do, thanks for the help! I'll post an update when I get one.

[u3b3rg33k]

If it's stalling when it's NOT at idle, it is probably something else, if it's just got idle issues, and everything else seems fine, it's more likely to be a cranky DME. check your model first before you spend money.

[Atara]

The issue only happens at idle, and it seems once the car is heated up after driving around for a while the problem disappears. I've taken it out a couple times for 15-30 minutes and when I get back I let it idle for 5 minutes or so and it doesn't have any problems.

[Atara]

Just went out and checked, looks like I do have a 173. http://img4.imageshack.us/img4/4639/image140i.jpg

[u3b3rg33k]

Might be best to check things like the throttle position switch, coolant temp sensor (the plug for the DME has two wires, the cluster gauge has one wire). Verify that the ICV is not stuck / slow to move (pull it off, use your finger to rotate the valve, it should move very easily).

Checking for vac leaks wouldn't be a bad idea either (cracked intake boot?).

[StereoInstaller1]

I put the fuse I had found back in and drove around a little bit and it seemed fine.

Journalism major, huh? You write well, thank you for being descriptive. Had you posted the year of your car, you would have been able to tell what DME you had, and then see if yours was correct...but all of that is a moot point: the "173 idles better" is basically bullshit. I mean it is a tiny bit better, but the 153 DME most certainly does not have a surging idle...they came in $30,000 cars in 1987! They do not suck, believe me, at their worst BMW is still excellent.

So: let me make this clear: the fuse has nothing to do with the idle issue. They are unrelated.

Look in the ETM, which can be found under "MANUALS" and then AUTOMOTIVE at www.wedophones.com do not forget to save a copy.

The idle is likely either vacuum leaks or a crappy idle air control valve, or just an IAC that is all gunked up. They can be blasted out with carb cleaner, it usually helps. Vacuum leaks can be hard to find. There is a thing called a "smoke testing machine" that blows thick smoke into the intake just to help spot leaks. If a careful inspection of the hoses do not reveal a leak, and going as far as swapping your IAC, you may wanna take it a shop for smoke testing. (I have one to recommend, BTW)

Since you have a 173 DME, you likely have a late model car which has a slightly different harness. There is a connection for the fuel injector harness directly under the throttle body. They can get pretty corroded and can cause running issues too, but not generally a surging idle.

Welcome to R3V.

Luke