Odd Idle Occurance Advice Needed. Not ICV/ICM Related.

[1SGDHORN]

ICV and ICM are both new. The car idles smoothly but, today when I went to put a radio in the glove box just for storage and tried to shut the door the radio pushed up against the plastic piece that covers what I believe must be the ECM and the car started to stall. Can I assume that the ECM may have some bad solder joints and the pressure from the radio pressing against it caused a loss in continuity that cause the motor to start to die out?

The secondary issue is that while under acceleration I can feel a very slight almost unnoticeable surging of how the power is applied. This is like the surging idle of a bad ICV but very, very slight almost unnoticeable. I wonder if this is ECM related as well?

[richardodn]

Sounds like either a bad solder joint or possibly a poor connection. You might want to try some DeoxIT on the contacts before replacing or cracking the old one open.

It's not likely you're getting an actual surge on acceleration. More likely you hit a flat spot in your acceleration. When it returns to normal you feel that as a surge. If it's a real surge, the system would be dumping extra gas in the system. In that case I'd recommend having your existing injectors cleaned and flow tested. If you live in a bigger city, there is likely someone that can do that local for <$200. If the flat spot is just off idle, it's likely a vacuum leak. If it is higher up in the RPM range it's likely the AFM. Specifically, there's a wiper arm in the electronics that moves with the vane over a resistance path. There might be a bad spot in the path. If you're handy, they can be opened up and bent slightly to let the arm travel over a fresh path. The DeoxIT might help here too.

[1SGDHORN]

Funny you mention all of this.

DeoxIT? I was thinking hitting the connector with some electrical cleaner and then using some dialectic grease on it. Or is using the grease not a good idea?

When I recently changed the plugs they were black and looked like they had been burning rich. Also, the tailpipe is very black and I sometimes think I can smell gas. The AFM is not original and looks like it may possibly be a rebuilt unit and I was thinking this could be the culprit as well. I have a spare ECM from an 1985 325e and as long as it is compatible I may swap it out and see if that makes a difference. I have considered having the injectors cleaned and for not much money replacing the FPR with a new one.

The "surging" is most felt at moderate speeds, 45 MPH or so, and under acceleration. At slower speeds and at idle I don't notice it and at highway speeds, 65 o 70 MPH I don't notice it.

[richardodn]

DeoxIT is a electrical cleaner specially formulated for removing oxidation. Dielectric grease is fine on just about any connection.

It does sound like the AFM is the issue. Exactly what is hard to say with the other symptoms. It's possible that the AFM was adjusted to make things "work." (Likely due to a vacuum leak somewhere.) I'd go find an unmolested used one and work with that.

[1SGDHORN]

I swapped in another identical ECM and no change. I swapped in a different AFM but the car would not run unless I constantly gave it throttle. The new ECM did not have the short issue so, even if that wasn't the issue at least I am thinking the swapped in ECM may be in better condition internally.

I replaced all the vacuum lines I could see/find shortly after buying the car. Other than one I can't see could this issue be caused by bad injectors or a bad FPR. It still does feel like an AFM issue but, the one on the car looks like a recent rebuild, not that it still couldn't be bad...

[richardodn]

That appears to have been a professional rebuild and is likely fine. Still, someone could have removed the red cap and adjusted it. It's hard to know what to do at this point. I'd drop in the original AFM for now since the car runs with that.

1. Chase down any and all vacuum leaks. Ideally you'd have a smoke test done. While testing, cap the connection on the throttle body where the evap hose connects to remove that system from the troubleshooting.
2. Pinch off the hose to the cold start valve after starting the car. If this leaks it might explain the rich condition.
3. Verify the right FPR is in the car. Should be a 2.5 bar on the 'e'. Take the vacuum line off while running and make sure no fuel is comes out. Any fuel would indicate a bad FPR and might explain the rich mix. If possible, verify the fuel pressure with a gauge.
4. Have the injectors cleaned and flow tested. Hopefully they're still the original Bosch units. Verify that.

[1SGDHORN]

I don't have another AFM to substitute in. The one I tried to use was out of a 1989 iX and though the car would run it would only run if I gave it constant throttle. It itself is an unknown as I have never driven the car that it came out of.

I was thinking a smoke test would be a good investment.

- I removed the vacuum hose from the FPR and no fuel came out.
- I assume the injectors are original.

Other observations if they matter and a lot of this is just "feel".

- The issue "appears" more pronounce when the car is cold.
- Idle is dead steady.
- When taking off from a stop under load and acceleration it is more noticeable.
- Not as noticeable at speeds around 45 to 65 and when under light to no load but is more pronounced at these speeds when under load.
- Not very noticeable at low speeds under say 10 to 15 MPH.

If not the AFM then I guess I need to eliminate any possible vacuum leaks.

I know it would be ideal if I could swap in a non issue, known properly functioning AFM to eliminate this as causing the issue, but unless someone in the Massachusetts area has one that is compatible with a 1986 325e I am left "hoping" the one in the car is a recent rebuild and not the cause of the problem.

[1SGDHORN]

I ordered a rebuilt AFM from my local O'reilys to swap in to see if this fixes the issue. If it doesn't they are allowing me to return it for a full refund minus what it cost to ship it to my local store.

Fingers crossed.

[1SGDHORN]

I made another discovery. It appears the surging idle does not happen when the car is cold. When I first start it and drive away the car runs nice and smooth. Once I have driven 2 or 3 miles and the car starts to warm up then the surging begins.


Suggestions?

I would guess a temperature sensor maybe? If so, which one?

[shadowracer]

I once had a similar issue myself. In my case it turned out to be the engine ground from the oil pan to the frame, it looked fine and a friend told me to physically grab and try to move it. I didn't want to believe that it could be the issue, but checked anyway. We did find that the bolt was loose on the oil pan, so we tightened it and all the issues stopped.

.....just something that won't hurt to check.

[1SGDHORN]

Easy enough to check and replace. It'd be nice if it was something that simple.