08 540I very rough start up and A/C sometimes does not work

[98540ibeamer]

I have a 5 series that has two problems that i need help with. I'm new to this forum and BMW in general. The first problem is starting up the car when its cold out. It idles but at low RPM, but sputters a few times until it warms up, then it runs fine. I have replaced the MAF sensor and cleaned the ICV.

The second issue is when i turn on the A/C or heater, it only works whenever it feels like. Yesterday the heater did not work, but this morning it did, same issue with the cold air. it blows air, but its just like room temp. If anybody has had this issue before or knows how to correct this i would really appreciate it.

[edjack]

Sometimes cleaning the ICV doesn't work, and it must be replaced. Did it rattle when shaken after cleaning? Did you poke anything inside it?

Your description of A/C-heat problem is vague: when the blower runs, does the A/C deliver cold air, and the heater deliver warm air? If so, the final stage unit is bad. Don't buy one from ebaY; get it from a supplier of OEM parts.

If the operation is not as I describe, the IHKA panel may be at fault. The BMW computer can interrogate the panel.

[mattmartindrift]

My 98 idles fine, but misfires (without throwing codes) for the first 1-5 minutes of driving if engine is cold and the ambient temp is <70ºF.

Other than that the car runs great....
I have pretty exhaustively looked for and tested for vacuum leaks. I've cleaned the ICV, and it holds a rock-solid idle at all other times.

I've replaced:
- all intake gaskets + CCV (during the Valley Pan job.).
- Cam-angle sensor
- MAFS
- Thermostat
- Thermostat-housing coolant-temp sensor
- spark plugs, and a few ign coils
- Air filter
- all 4 O2 sensors

At this point, the only thing left that I could see as a cause is the remaining coils, and Crank-Position Sensor. More remotely, perhaps the other coolant temp sensor, knock sensor(s), and fuel injectors.

[98540ibeamer]

Sometimes cleaning the ICV doesn't work, and it must be replaced. Did it rattle when shaken after cleaning? Did you poke anything inside it?

Your description of A/C-heat problem is vague: when the blower runs, does the A/C deliver cold air, and the heater deliver warm air? If so, the final stage unit is bad. Don't buy one from ebaY; get it from a supplier of OEM parts.

If the operation is not as I describe, the IHKA panel may be at fault. The BMW computer can interrogate the panel.

When i cleaned the ICV, i didnt stick anything in it, i just used the choke and carb cleaner like the forum on this site explained. dont get me wrong, it ran so much better after i cleaned it out because the door in the ICV would even move with so much build up. Also the MAF was new, even after that it ran really clean and quiet. As for the a/c, when it blows it blows only dry air, its not cold, just dry, same temp air comes out when i turn the heater on. is there any way to test this system out to see which part is damaged. As far as the final stage, where would be a good place to buy it. Thanks for the reply

[edjack]

Best place to get the FSU is from a reputable seller who deals only in OEM stuff. Check out the supporting vendors.


mattmartindrift,

Did you clean the ICV? It is supposed to be closed after the engine reaches a certain temperature. The purpose is to speed up the idle when cold, due to the drag of cold oil.

If the crankshaft position sensor were bad, the car would crank, but not start.

[mattmartindrift]

Best place to get the FSU is from a reputable seller who deals only in OEM stuff. Check out the supporting vendors.


mattmartindrift,

Did you clean the ICV? It is supposed to be closed after the engine reaches a certain temperature. The purpose is to speed up the idle when cold, due to the drag of cold oil.

It does not close after a certain temp. However, it does open and close to regulate idle at all times, cold warm, and with the AC on - controlled by the DME.

Yes, I have cleaned it.

If the crankshaft position sensor were bad, the car would crank, but not start.

Not exactly true. It's a magnetic reluctor sensor, which can progressively fail. My theory in this case is that the signal generated is weak with the cold engine. However, as the flywheel heats, it expands enough to close the flywheel-to-sensor gap. Allowing the mag sensor to generate a clean enough square-wave signal for the DME to interpret - iirc, the specified gap is supposed to be 0.020" when replacing the sensor.

[98540ibeamer]

It does not close after a certain temp. However, it does open and close to regulate idle at all times, cold warm, and with the AC on - controlled by the DME.

Yes, I have cleaned it.



Not exactly true. It's a magnetic reluctor sensor, which can progressively fail. My theory in this case is that the signal generated is weak with the cold engine. However, as the flywheel heats, it expands enough to close the flywheel-to-sensor gap. Allowing the mag sensor to generate a clean enough square-wave signal for the DME to interpret - iirc, the specified gap is supposed to be 0.020" when replacing the sensor.

So your saying the crankshaft position sensor is a good start?

[mattmartindrift]

So your saying the crankshaft position sensor is a good start?

Not necessarily. I was explaining my theory to edjack as to why I think it could be to blame for the issues without having a 100% failure.

I'm hesitant to drop ~$100 and my time on an untested guess. Especially when it doesn't seem to affect anything after being warmed up.

[Cyrix2k]

Not necessarily. I was explaining my theory to edjack as to why I think it could be to blame for the issues without having a 100% failure.

I'm hesitant to drop ~$100 and my time on an untested guess. Especially when it doesn't seem to affect anything after being warmed up.

I'm pretty sure the DME would set a code if it wasn't receiving a clean signal from that sensor. That particular sensor measure the crank angle very precisely and determines if the engine is misfiring based on that information from what I read in a BMW whitepaper.

Since your problems occur during the first cold start, I'd look at what is unique to that situation which off the top of my head would be cold start fuel enrichment & open loop operation. I wouldn't be surprised if you're lightly fouling a few plugs or running rich during the initial start; my e30 would misfire for the first few minutes when I had it injecting too much fuel during cold starts. The crank sensor would almost certainly continue to show symptoms after the car warms up.

[mattmartindrift]

I'm pretty sure the DME would set a code if it wasn't receiving a clean signal from that sensor. That particular sensor measure the crank angle very precisely and determines if the engine is misfiring based on that information from what I read in a BMW whitepaper.

Since your problems occur during the first cold start, I'd look at what is unique to that situation which off the top of my head would be cold start fuel enrichment & open loop operation. I wouldn't be surprised if you're lightly fouling a few plugs or running rich during the initial start; my e30 would misfire for the first few minutes when I had it injecting too much fuel during cold starts. The crank sensor would almost certainly continue to show symptoms after the car warms up.

Since my DME is stock, and cold-running enrichments haven't been touched, I'm hesitant to look in that direction. IIRC, all other items related to cold-running, sans coils, have been replaced. Sensor data was also verified in INPA.

- open-loop = O2 sensors aren't in play, despite them having been changed.
- The problem continued with fresh plugs.
- MAFS was replaced
- 4-pin coolant-temp sensor was replaced.
- Cam sensor was replaced
- Air leaks were checked + air-intake system rebuild.


If the DME were to throw codes for the crank sensor, it would be a random misfire (signal not strong enough, but angular acceleration wasn't what the DME expected based on extrapolation) - I have had occasional random misfire codes in the DME's "shadow" memory.


I have witnessed cars with faulty crank sensors, displaying the symptoms I described. One in particular was a Nissan 350z race car with an aftermarket flywheel that was mucking with the crank sensor.

[Flug540]

I have the same exact symptoms in my '98 540i. Last time it was so bad I even had to depress the accelerator or it would stall otherwise. After it warmed up, it was fine. I have an A/F gauge installed and I see that the mixture is extremely lean at cold start. After it warms up, the mixture becomes normal between 14 and 15. But sometimes it idles more on a lean side (around 16ish) even when running under operating temperature. When it idles warm around 16-17, I can hear a slight change of tone in the engine, but RPM stays about the same and normal (maybe a slight dip).

At first I suspected injectors, but if the engine runs fine at high RPM, that couldn't be it, right?

As you guys, I cleaned MAF, ICV, throttle body, cam position sensor was replaced not too long ago, no codes. This weekend I'm going to test the intake for leaks and go from there.

BTW, here's a very good guide about MAF testing.

[mattmartindrift]

lean idle is normal, when I tuned my cars, I always would setup the idle to be as lean as possible before it would start to sputter.

[Flug540]

lean idle is normal, when I tuned my cars, I always would setup the idle to be as lean as possible before it would start to sputter.

My gauge reads up to 18 and on cold idle it maxes out and then the engine dies.

Do you know where on the scale you set your idle mixture?

[mattmartindrift]

My gauge reads up to 18 and on cold idle it maxes out and then the engine dies.

Do you know where on the scale you set your idle mixture?

all depends on the engine, fuel, plugs and other variables. the cars I tuned were track-only, but i would see as high as 17:1 when warm. Cold will require extra fuel.

Also, it's a good idea to confirm your WBO2 sensor is fresh and the hardware is properly calibrated (if there is a calibration function at all). Is it placed pre- or post-cat?

[Flug540]

all depends on the engine, fuel, plugs and other variables. the cars I tuned were track-only, but i would see as high as 17:1 when warm. Cold will require extra fuel.

Also, it's a good idea to confirm your WBO2 sensor is fresh and the hardware is properly calibrated (if there is a calibration function at all). Is it placed pre- or post-cat?

It's pre-cat and practically brand new.