Warm Starting Issue

[H8Rain]

First let me say, I did do a lot of searching, but the issues or results were not exactly what my issue is.

So with that said, here is my Warm Start Issue:  When the car|engine is cold (summer or winter) say the first start of the day.  It cranks and then turns over right away (I would say within 2 seconds).

However, once the car has been driven for a while and reaches operating temperature, then turn it off.  When you go back out to start it again (say within 10-15 minutes) it takes almost 5-7 seconds of cranking until it turns over.

Once it does turn over there are no other issues (such as hesitation or rough idle).  It doesn't struggle to crank (new battery solid starter).  

So the problem is strictly when it's hot it just takes much longer to turn over?

I have done a thorough tune up:

- Plugs
- Wires
- Fuel Filter
- Air Cleaner
- All fluids

Thoughts?

Thanks so much!

Mark

[DesktopDave]

How old is the O2 sensor?  I'd also test the resistance on your intake and coolant temp sensors.  Should be very high at cold temps and drop dramatically as it warms up to operating temp.  I don't have the BMW manual handy, but it's something like 10kohms cold and 300 ohms hot.

You can do a stomp test too, if it's a US-spec car.  I think 1224 is a bad coolant sensor, 1221 is a bad O2 (likely that's a vac leak though).

IIRC the IAT is pins 4&5 on the AFM plug, CLT is the two-pin (forward-most) sensor bolted into the driver's side of the head.

[DesktopDave]

Found it:

According to the 3 series repair manual:

Intake air temp sensor @68degF 2200-2700 ohms; at 122degF 760-910 ohms.
Coolant temp sensor is very similar: @58degF 2300-2700 ohms; at 180degF 300-360 ohms.       

[H8Rain]

Great.  I will do the testing and let you know what I find.

Thanks.

[H8Rain]

PS:  I do not know how old the O2's are.

[Geoff]

admittedly,  this has not happened to my e-30.   but on a volvo I used to have,  leaky injectors would drip after the car was shut off, and make it hard to start 10 minutes later.   If it sat all night,  the gas would evaporate, or leak down into the crankcase, and the car would start as normal.    I am not sure if the bmw injectors tend to do this also or not.
                                                                       Geoff

[H8Rain]

ok, ran the test......

- Stomp Test:  I got 1444.  So no codes.
- Coolant Temp Sensor (hot) I got 260 ohms
- Intake Air Sensor (hot) I got 1850 ohms

I didn't test any of the sensor cold (like in the morning) since my problem really isn't a cold start, it's a hot start.

So the one that stands out is the IAS..... correct?

Let me make sure I did this correctly.  The car had just returned from a 30 minute drive so it was good and hot.  I did the ohms test with the car turned off, correct?  For the IAS I twisted the connector off of the AFM and touched the pins with my meter, correct?

So I'm guessing your gonna say I should start by replacing the IAS.  However, can you replace just the IAS on the M42???  I can't find that part alone???  Please don't tell me it requires replacing the entire AFM?

As always, thanks so much for the help!!!!

PS:  Geoff - I did do some research on the leaky fuel injectors.  That is a good suggestion, however everything I found said that usually results in a "cold-start" problem, as the injectors tend to leak as the car sits for a while and then gets cold (like say overnight).  As you said, the cylinders have too much gas in them and it then takes more "cranks" to get it started.  But again, when cold.

[bmwman91]

Did you have the black plastic wiring cover (up on the firewall) off at any point? There is a little single-wire connector up there that is disconnected on cars with O2 sensors. A lot of people mistakenly reconnect it thinking it came loose, and then have this sort of issue. It is the connector for the AFM's LLCO output, which is not used on cars with O2 sensors.

Other than that, I can't really think of anything obvious that wouldn't also cause it to run badly when hot. Actually, the connector I mentioned probably would make it run poorly, so maybe it isn't that.

Maybe it is a bad fuel pump relay that heats up & stops working? When it is hot, can you hear the fuel pump prime itself when you turn the key to accessory mode?

[Xraycat]

I have exactly the same problem, very embarrassing when sitting outside the local shops. I have just removed my idle control valve to find most of the breather pipe work perished so I'm sorting that at the moment. I shall keep an eye on this one