Engine dir and won't restart

[Jay 535i]

PLEASE HELP!

My car has developed a new problem. The engine will die and not restart. Battery and feel level are fine.

The car will ultimately start after several tries, but then idles roughly or too high, and usually dies again. Then it may run fine for several hours.

While it's idling roughly, goosing the gas will either do nothing, or will cause the revs to drop.

The coolant temp. sensor is throwing a CEL occasionally over the last couple of weeks, if that could have anything to do with it. This new problem arose yesterday and persists today.

Thanks in advance for any help. Let we know if you need more info.

[Ferret]

Air leak into the manifold, or your MAF has died.

Check all the thick black air hoses around the throttle body - they're about an inch wide. One may have fallen off, then check if the air trunking between the MAF and throttle body is secure.

[Jay 535i]

Thanks Ferret.

This happened again since I first posted. It took ten minutes of (non-continuous) cranking to start it again, then it ran rough for a couple of minutes, then ran perfectly for ten before I shut it off.

The air hoses seem fine, but it's pretty hard to tell.

Still no fault codes, except for the coolent temp sensor, which only throws a CEL for a few seconds out of every trip.

Any more diagnosis tips or second opinions?

[Jr ///M5]

Check the Crank Position Sensor, make sure it's clean and not loose from the bracket.

[Jay 535i]

Check the Crank Position Sensor, make sure it's clean and not loose from the bracket.

Where's that and what does it look like?

Thanks JR.

[bmw540]

check spark plugs

either electrical or fuel

fuel filter blocked

what happens when the engine runs smooth and you rev it. does it break down and splutter?

check charging volts

[Ferret]

Try starting it with your foot on the gas and see what happens?

Then try starting it with the MAF unplugged.

Jay - on the 535 the crank sensor is located above the front flywheel iirc - it's a cylindrical metal can about 1/2" across that sits with its front facing onto the top of the notched part of the flywheel. Should have a cable running up and around the side of the head by the oil filter. (Though dont quote me on that last bit, I cant remember if mine went off to the right hand side of the car or not)

[Ferret]

AH! hang on - if your coolant sensor is telling the computer the engine's warm, it wont start properly from cold at all. Let it get up to temperature just idling badly and see if the idle improves when the engines warm.

[Jay 535i]

Many thanks.

BMW540, when the engine's smooth and I rev it, it's fine -- 100% normal. Then it'll die for no reason at all when (and only when) I let it drop to idle.

Ferret, the problem seems more prevalent when the engine is warm rather than cold. I guess replacing the temp sensor is the first order of business. OTOH, the temp sensor has been throwing a CEL for about six weeks, and this new problem only arose two days ago, so I'm not sure they're connected. OTOH again, may the sensor has been dying slowly and it's just now getting critical. I don't really know enough about how this stuff works to figure it out.

Let it get up to temperature just idling badly

It won't idle badly. It either idles and runs perfectly, or not at all.

What does the coolant temp sensor do, besides making the needle on the dash move?

[Ferret]

Unless your temp sensor is causing a short circuit, it shouldnt affect how the vehicle's running - it should default to get you home mode - runs like **** but it'll run. Sounds like you've got something more serious going on. I've only got two seconds atm, I'll post again in a bit.