Rough running 318i M10

[Jona1971]

Hi,
my new pride and joy I haven't had long - the previous owner said all it needed was a new Idle Control Valve...
Well so far,
1. new ICV
2. new Air Flow Meter
3. new fuel pump relay (2 in the glove box when I bought it)
and its still runs rough until warm then runs perfectly.
Quite by chance I leant on the connector to the Coolant Temperature Sensor and it ran better. Symptoms are: idles low at 500rpm, slow pick-up, cuts out, stalls, won't start. Then, give the connector at the top of this sensor a waggle and the revs pick up to about 850rpm and it runs fine again.
I've swapped the connector, removed the connector and soldered on spade connectors instead, still no good.
So, new temperature sensor then?
Or, what else could be going on?
Thanks muchly,

[Brianmoooore]

It's quite common for a failed temperature sensor to be affected by external pressure applied to it, so I would say it's time for a new one, but first you should do what you (and the previous owner) should have done at the start - test the resistance of the sensor at the appropriate pins of the ECU plug (NOT at the sensor), first with the engine stone cold, and then with it at full working temperature

[BenHar]

http://www.e30zone.net/e30zonewiki/inde ... or#Testing

Ben

[Mitchen]

If it is down to the C191 (seems to be alot of these coming up recently) What do you do? Replace? Repair? Am I right in thinking a new harness is around £800

[BenHar]

You can just cut the c191 out and connect the wires.

Don't ask me how I know that either.

Ben

[Mitchen]

You can just cut the c191 out and connect the wires.

Don't ask me how I know that either.

Ben

Haha are you not just prolonging the issue though? The wire has still had 25 years or so of moisture exposure, so will fail again no?

[BenHar]

It's where the wires join the connectors that it breaks.

Easy enough to cut back to good wire and join it.

Ben

[Mitchen]

Ahh fair enough, that does sound cheaper than paying £800 for a wire.

[Brianmoooore]

C191 is only fitted to facelift six cylinder engines, so you won't have to worry about that with this engine.
A TIS was issued by BMW for a simple modification to solve the C191 problem, but a good number of E30s haven't visited s dealer since and had the mod. performed.

[Mitchen]

Brian would this indicate that my car's had the fix and my car wont suffer from any C191 issues?

[BenHar]

The C191 Tis was just to make a drain whole in the bottom rubber boot of the plug.

Ben

[Brianmoooore]

Brian would this indicate that my car's had the fix and my car wont suffer from any C191 issues?

Nothing in that pic. that I can see to indicate that any C191 issues have been attended to.
The relay on the fusebox is probably BMW's 'fix' for engine flooding on cold start up. It's mentioned in the wiki on the relays page.

[Brianmoooore]

The C191 Tis was just to make a drain whole in the bottom rubber boot of the plug.

Ben

It is indeed, but solves the problem.

[Jona1971]

Thanks all, I'll get my multimeter out and have a go...

[Jona1971]

OK, checked at pins 10 and 13 of ECU plug (my multimeter skills a bit rusty):

Cold
1750 (200k setting)
1 Ohm (200 setting)

HOT
2 (200k setting)
225 Ohms (200 setting)

[Grrrmachine]

Think you got your HOT settings the wrong way round (a meter set to 200 can't read 225). But that would suggest that your temp sensor is working, and the signals are getting to the ECU.

[Jona1971]

No, I couldn't get a reading COLD unless on the 200k scale when I got 1750.
Then, when HOT I couldn't get a reading on the 200K scale unless I turned it to the 2000 scale (sorry, my mistake not the 200 scale).
Anyway, lots of resistance when cold and less when hot, as it should be?

[Mitchen]

Nothing in that pic. that I can see to indicate that any C191 issues have been attended to.
The relay on the fusebox is probably BMW's 'fix' for engine flooding on cold start up. It's mentioned in the wiki on the relays page.

Funny thing is the wire from the blue sensor in the stat housing, seems to run all the way along to that relay. I can't see any C191 plug, or anything else interfering with it, other than another blue plug/connector which is about 6-8 inches along the lead from the actual blue sensor.

[Mitchen]

Don't mean to hijack the thread Jona. Apologies

[Grrrmachine]

Mitchen, please stop hijacking other people's threads - it makes things very complicated to fix.

To keep you quiet, read this:

http://www.e30zone.net/e30zonewiki/inde ... tart_Relay

[Jona1971]

Thats quite alright, just wonderring where to go next.

[Grrrmachine]

How cold was the engine when you got the 1750 Ohms reading? I'd expect a Blue Temp Sensor to be reading more like 3000-4000 Ohms when cold.

Still, if you're sure that wiggling the connector got the car running better, then you must have a loose connection there somewhere. Possibly an earthing issue?

[Jona1971]

Car had last been driven about 2 hours earlier.

I'd read about the Blue temp sensor on WIKI but had trouble finding mine. My brown plug is brown but my blue plug is black. I don't know if I've got the wrong one fitted but I'll find out in a couple of days when my New Blue Bosch one arrives and I fit that.

There seems to be a bit of green furry corrosion around the nut so I'll make sure its all clean and earthed when I fit the new one...

[Jona1971]

Right, I left it all night so its stone cold and on the 2000k setting I got 490 and when hot it read 35

[Brianmoooore]

Instructions for using an ohmmeter: Switch to the highest ohms range, connect leads, then progressively switch towards the lower ohms ranges until the meter reads overload (often a single '1'). At this point switch back one range and read the dial.

[Jona1971]

Thanks:

Cold - it read 490 on the 2000k scale
Hot - it read 44.6 on the 200k scale

after that it read "1" as you described.
Thanks,

[Brianmoooore]

In that case your readings are massively higher than they should be.
Your reading, cold: 490,000 ohms. Should be 2500 - 4000 ohms, depending on ambient temperature.
Your reading, hot: 44,600 ohms. Should be around 330 ohms.

[Jona1971]

Right, thanks.
Would that mean a faulty temperature sensor or something else?

[Grrrmachine]

More likely faulty useage of the Multimeter, as there's no way a blue plug is going to put out 490,000 ohms. I expect your readings are actually 4900 ad 446 ohms.

Presuming you really are struggling to use the meter properly (or are confusing "k" with "Ω") then it's the difference in readings that matters, and it seems your blue plug is changing resistances by the expected amount, and that the fault is elsewhere.

I think this is going to be something really annoyingly simple like an air leak.

[Brianmoooore]

More likely faulty useage of the Multimeter, as there's no way a blue plug is going to put out 490,000 ohms. I expect your readings are actually 4900 ad 446 ohms.

I tend to agree with this as well, but those readings are far enough out to cause considerable running problems if the cold reading was taken at current UK temps., and the hot reading was taken before the coolant had started to cool appreciably .

[Jona1971]

Thanks both, but the car runs beautifully when warm. (I would have thought an air leak would cause rough running all the time?) It just runs badly until it's at temperature.

[Brianmoooore]

Looking back at the OP, you say the running is affected by finger pressure on the blue temp. sensor.
This indicates a possible crack in the NTC sensor element, which is consistent with the high resistance readings.

[Jona1971]

Yes it is. When I put pressure on the connector the car seems to start running right.
Once, I broke down and the car wouldn't start. I waggled the connector and in started right up again and ran OK.

[Brianmoooore]

Time for a new one.