M50tu won't idle and it's not the MAF or a vac leak

[cohny]

I have an e34 but I'm hedging my forum use here. For a couple of days the idle degraded on my e34 525i until it wouldn't idle any more at all. I unplugged the MAF and the car idled fine. I took it to my shop and he told me get another MAF because everything else worked fine. I bought one on the classifieds here and threw it in. There was no improvement despite the fact that I tested the new MAF on a buddies car and it worked fine.

I know that it can't be a vac leak. I replaced the intake boot and the car works fine without the MAF. There's no way it would run ok in alpha-n if there was a vac leak. I have no idea what to do about this and I really need to get this car up and running so I can get back to a normal commuting schedule. Any ideas? I'm totally at a loss here.

Thanks

[e36fiend]

What happens when you put your buddy's MAF in your car?

[UnderCoverGuy11]

Makes me think ICV and TPS, cleaning the ICV is free so start with that, then test the TPS

Edit: does the car run at least if you hold it above idle?

[cohny]

What happens when you put your buddy's MAF in your car?

When I put my buddy's MAF in my car there's no improvement. The exact same thing happens.

Makes me think ICV and TPS, cleaning the ICV is free so start with that, then test the TPS

Edit: does the car run at least if you hold it above idle?

It will, yes. I can keep the car going indefinitely with the throttle. It's just the idle that isn't functioning. I need to check the ICV, but the idle seemed to die much faster than would seem reasonable if it was the ICV. It was sort of pulsing before it stopped idling completely. It would go vroom..vroom..vroom..vroom over and over and over again, and then one day it just wouldn't at all. That progression happened in like 2 days which makes me think its an electrical issue of some kind.

Also, if I understand correctly, when the MAF is disconnected the engine maximizes fuel input and runs completely off the TPS. So if the car is operational with the MAF disconnected, I'm led to believe the TPS can't be the problem.

[legoman67]

Did you ever figure this out? I have a car with the exact same issue. Except this one also runs the same with MAF unplugged. Cleaned and tried a replacement ICV with no luck either. Suspecting DME or bad wiring at this point

[Eric93se]

I believe the car should die when you unplug the MAFS (when its good), when the sensor is bad the car will continue to run. Be careful of aftermarket MAFS their are some total junk ones out there, instead of the hot film elements they put some varistors or something on there. So stick to the OEM brands.

Also when a car hunts aka. "vroom..vroom..vroom" that is typically a vacuum leak, so if you cannot visually find the leak or use carb cleaner or some other flammable substance that the vacuum can suck in and give a noticeable idle change then you have to smoke test it.

[ed323i]

I believe your car will run just fine without MAF. You'll notice a little hesitation when going on the gas from idle, but for the rest it should run just fine.
I've run my 323i M52 without MAF for weeks without any problems. It even seems to develop full power. Your DME, Motronics 3.3.1 if I'm correct, might be a little less advanced than the Siemens MS41, but I think it can do the same, running perfectly fine in Alpha-N mode.

If it runs and idles fine without MAF, there can't be a major problem with the TPS or ICV, crank/cam position sensor, vacuum leaks, coolant temp sensor, air temp sensor, oxygen sensor, etc.

My conclusion so far is that there is probably a problem in the wiring between the DME and the MAF (find the Bentley manual and check if all MAF wires end up at the pins of the DME), or something has gone wrong inside the DME (replacing it would be your best bet; if it has EWS then use the great ewssync.exe tool; INPA not needed, or have it synced by someone who has the tools for the job).

P.S. I used to have an E34 525i M50 (no Vanos though) and loved it very much. The power-weight ratio of the 323i (and the low-end torque) does make it more fun, but on the highway and longer trips, the E34 was really great, especially between 4000-6500rpm. Was really impressed by the great German engineering, and the rock-solid feel of the E34 chassis.

[Eric93se]

I stand corrected on the MAFS, had to go outside and see if it would start with it unplugged and it did. I don't see how this is an EWS issue and I wouldn't recommend using EWSSYNC if there is nothing changed that would effect it.

[ed323i]

I stand corrected on the MAFS, had to go outside and see if it would start with it unplugged and it did. I don't see how this is an EWS issue and I wouldn't recommend using EWSSYNC if there is nothing changed that would effect it.

I meant to write that in case the DME needs to be replaced, and if it has EWS, then he can use the ewssync tool to resync the EWS to the new DME..

P.S. Thanks for confirming that you car can run without MAF.. I'm quite certain the Motronics M50B25TU can also do it, but perhaps a bit less efficient/advanced/smooth as the Siemens MS41.

[ultimatetester]

I believe your car will run just fine without MAF. You'll notice a little hesitation when going on the gas from idle, but for the rest it should run just fine.
I've run my 323i M52 without MAF for weeks without any problems. It even seems to develop full power. Your DME, Motronics 3.3.1 if I'm correct, might be a little less advanced than the Siemens MS41, but I think it can do the same, running perfectly fine in Alpha-N mode.

If it runs and idles fine without MAF, there can't be a major problem with the TPS or ICV, crank/cam position sensor, vacuum leaks, coolant temp sensor, air temp sensor, oxygen sensor, etc.

My conclusion so far is that there is probably a problem in the wiring between the DME and the MAF (find the Bentley manual and check if all MAF wires end up at the pins of the DME), or something has gone wrong inside the DME (replacing it would be your best bet; if it has EWS then use the great ewssync.exe tool; INPA not needed, or have it synced by someone who has the tools for the job).

P.S. I used to have an E34 525i M50 (no Vanos though) and loved it very much. The power-weight ratio of the 323i (and the low-end torque) does make it more fun, but on the highway and longer trips, the E34 was really great, especially between 4000-6500rpm. Was really impressed by the great German engineering, and the rock-solid feel of the E34 chassis.

It won’t produce more power all the way. With the maf unplugged the engine will use the same map as in an open loop situation. This means that most other sensors will also not be used. This safe map is very rich so not the best for your fuel economy. It’s safe map so no it won’t hurt too much..

[ed323i]

It won’t produce more power all the way. With the maf unplugged the engine will use the same map as in an open loop situation. This means that most other sensors will also not be used. This safe map is very rich so not the best for your fuel economy. It’s safe map so no it won’t hurt too much..

Thanks for the addition. I think you might be right, but not 100% certain (see last paragraph below). Now I think of it, I was comparing open-loop with MAF to open-loop without MAF, as I had an O2 sensor disconnected at the time. And then there is no noticeable difference (no MAF even seemed better as my MAF was a cheap ebay piece of shit). It runs quite smooth in alpha-N, but looking back, I think you're right it doesn't develop full power.
Later, I indeed noticed that open-loop develops less power. During open loop mode, the knock sensors are also disabled (confirmed in the romraider MS41 forum, where they dis-assemble the entire Siemens DME), and the ignition is retarded quite a few degrees, and that's what causes the lower power output.

Another theory I had is that most tuners don't tune the Alpha-N (MAF disconnected) mode. So, as my DME is tuned, I notice a decrease in power when I disconnect the MAF, because it reverts to the factory Alpha-N map instead of the optimized tuned MAF-connected map. So, at this time, I can't confirm what really causes the power drop. It seems sensible that in my case it's both factors: no tuned Alpha-N map, and safe/open-loop mode with retarded ignition map and disabled knock sensors.