Cold Stumbe

[sharky]

Hi Guys

This problem has me beat for now.

My car runs fine when warm but when first started from cold it has a stumble/splutter.

Start it from cold stick it in reverse or drive slightly press the loud pedal a fraction to say reverse out of the drive and it will stumble splutter and sometimes stall.

If you select drive though and nail the loud pedal it will take off coughing a bit and then bang all seems to clear and all is ok.

I have taken the AFM and cleaned it and the gate, renewed all the vaccum hoses, new spark plugs, new HT leads and new fuel pump. Checked the setting of the throttle switch and cleaned it. I have also put in a new temp sensor and ICV.

Anyone have any suggestions

[mrLEE30]

Check the blue temp signal at the ECU

remove the ECU plug and identify pin 45 and pin 2 on the cable side (pin 45 should be brown/red wire going to it, pin 2 has brown)

then set you meter to measure resistance.

with the engine completely cold measure from the pin 45 to ground, and then from pin 45 to pin 2, the resistance should be about 2-3000 ohms for each case. now refit and run the car till hot, remove and re measure and you should have 2-300 ohms for each case. If this does not happen then report you findings.

[Brianmoooore]

Checked the setting of the throttle switch

How/what have you checked?
How long since the injectors were serviced?

[sharky]

Hi

Have checked that as soon as the throttle moves the TPS clicks. The injectors are 168000 miles old, I have just bought some 19lb mustang ones but have not put them in yet, these are my next attempt to fix the problem. If they don't cure it I might just go mad. lol

[Brianmoooore]

At 168,000 miles they should be just about due for their second or third rebuild!
Getting them refurbished (£10 each) is a far better idea than fitting a set of incorrect injectors.

[e301988325i]

If you fit 19lb injectors your can't won't start or run.

Has the AFM been adjusted in the past?

[sharky]

Oh sh*t

Was told the mustang injectors would work as the motronic would adjust to them.

The standards are supposed to run lean at the top end.

Others suggest using a 2.5bar fuel pressure for a while and then switch back to the 3 bar.

So I guess the above is not true.

[kam-325i]

They dont run lean, just MAX out......

[e301988325i]

am i the only one still guessing what engine we're dealing with?

[sharky]

lol

325i 1989 Cab, I was wondering when someone would ask that. lol

Have one of these fitted.

325i/525i Chips for M20B25 with 173/380 ECU code:
3. EcoTorq M20B25 Mild; 7-11bhp gain, significantly enhances the torque for driveability/improved fuel economy (expect at least an extra 2-3mpg average) and eliminates flat spots, also a 6900rpm rev limit. An ideal blend for daily motoring, also works well with automatics.

[mrLEE30]

i would love to know how a chip gains HP and saves fuel too, bet BMW would pay quite a lot for this ability!

when you say you "checked and cleaned the Thorottle switch" how exactly did you check it.

[sharky]

Hi

Have checked that as soon as the throttle moves the TPS clicks.

Opened it up also to check no oil or dirt in it.

Just come to work in the car, 30 miles, now it is warm you slightly press the accelerator pedal and no stumble/splutter, it 's fine, only when cold do I have the problem.

[sharky]

Update

I have now checked the TPS with the throttle body of the car.

Set the butterfly with a piece of A4 paper and set the TPS so a soon as the throttle moves you get a click to say the car is now off idle.

With a meter I have checked that the TPS has continuity when the throttle is closed and when the throttle is nearly fully open, so that is as it should be.

When the TPS is connected to its plug with the ignition on pin 3 has 10.5 volts, I believe it should be 5 volts, is this a problem ? does it mean the TPS is duff ?

Anyway with the throttle body and TPS back on the car I still get the stumble stutter when cold just of idle in drive with the accelerator slightly pressed, when the car is warm it runs like a dream.

I have now changed the Injectors, ICV, FPR and AFM and I still have the stumble stutter when cold just of idle in drive with the accelerator slightly pressed.

Don't know now what the problem could be, I am sick of it to be honest.

[e301988325i]

good work, you need to get the mixture set on a gas analyser, 1% co

[sharky]

Right Sorted, Yeahhhhhhhhhhhhhhhhhhhhhhh

It was the naffing AFM, the replacement was slightly duff also.

With the original AFM with pins 7 and 8 connected to my ohm meter I set about testing the resistence of the air flap.

The initial reading was 2 Ohms, as soon as you moved the flap a little the resistence dropped to 1.6 ohms, moving the flap a little more caused the resistence to increase up to 2.5.

This drop and rise in resistence continued the further you moved the flap i.e readings went up and down on the ohm meter.

The replacement AFM I got had a problem with the flap in that it did not move freely.

I cured this with a bit of WD40 and then checked the flaps resistence with my ohm meter on pins 7 and 8, it gave the appropriate increasing resistence and no dips.

I then stuck this AFM back on the car and the stumble/stutter just off idle, in drive, when cold has gone.

Wicked

[PG325]

Mine does exactly as yours, after a minute or so of driving it sorts itself, the ohm figures throughout the movement of the AFM flap are jumping all over the place, hopefully my replacement AFM will resolve this.

[sharky]

I reckon it will PG325.

[Brianmoooore]

You won't test an AFM properly with an ohmmeter!
You need to connect a battery across the ends of the pot. track and monitor the voltage on the wiper as you move the flap by hand.

[sharky]

Like this.

http://www.the944.com/afm.htm

[mcbonio]

Sorry to hijack this thread,
I have a similar problem when my 325i is cold, until the engine temp is in the middle, the car chokes up when I press the accelerator.

As I blip the gas, it chokes and hesitates for a second then revs. If I rev it past the idle map to the running map and bounce the revs from 1500 to 3000 its fine, nice and resonsive.

It also is running a little rich, exhaust always smells of fuel even when engine is hot, theres always a little white smoke from the back too.

It idles stable, albeit a little low, around 650 rpm. Never stalls.

What might this be? old AFM?

[mrLEE30]

What might this be? old AFM?

Check the blue temp signal at the ECU

remove the ECU plug and identify pin 45 and pin 2 on the cable side (pin 45 should be brown/red wire going to it, pin 2 has brown)

then set you meter to measure resistance.

with the engine completely cold measure from the pin 45 to ground, and then from pin 45 to pin 2, the resistance should be about 2-3000 ohms for each case. now refit and run the car till hot, remove and re measure and you should have 2-300 ohms for each case. If this does not happen then report you findings.

or check TPS as described above

[mcbonio]

Cheers MrLEE,
Will do that tonight.! How do I test O2 sensor too?

[sharky]

Mcbonio

Your problem is exactly or was exactly the same as mine, I checked all these Temp sensor, Injectors, ICV, TPS wiring rail for injectors, fuel pump, fuel filter, CPS and it was the AFM all along. Your problem will be the same in that when the AFM is cold the air flap must be doing it own thing but as soon as the car warmed it was fine and is now 100% with replacement AFM.

I checked the resistance on the air flap as given in the Bently Manual and Haynes version and the resistance dipped as soon as the air flap moved and did the same the more you moved the flap.

You can check the voltage on the AFM with the link I gave above.

I bet though it is your AFM.

[mcbonio]

Cheers Sharky,
I have a Bentley manual here, I'll begin by checking coolant sensor, O2 sensor and AFM tonight. The first 2 are easiest to check, won't hurt to rule them out.

Did you get another used AFM or a new one? If so where from and how much?

I'll get back to you later on tonight.!

[mcbonio]

Ok my ECU is the 35 pin version btw, so pin 5 is ground and pin 13 coolant sensor....

The coolant temp sensor reads,

Cold = 3800 ohms
Hot = 260 omhs

Outside temperature is 8 degrees and I took at 10 minute drive after cold reading, temp gauge was bang in the middle when hot reading was taken.

So if its supposed to be between 2-3000 when cold , surely 3800 is out of range? Is the sensor giving a bad signal when cold but ok when hot?

What shall I test next? O2 sensor, AFM?

[sharky]

Mcbonio

Must admit I checked the resistance across the 2 pins on the sensor itself, from what I read this should be 3Kohm when cold.

It was a secondhand AFM that had not been used for a while, it was of a 90000 mile car, mine had 168000 on it.

The air flap was sticky so a bit of WD40 sorted that and then after checking it stuck it on the car.

The car has no stumble when you slighty push the accelerator from cold or on hard acceleration from cold no choking like it had.

Push the accelerator a little now when cold and it wants to go, on hard acceleration when cold there is no choking either.

Its a rocket now at any temperature.

The AFM was £9.00 off Ebay so if it didn't work I hadn't lost much compared with £250 for a new one to find out it didn't sort the problem.

I am now going to buy another one of a low mileage car for spares.

Change the AFM.

[mcbonio]

Ok I've just tested the AFM, it reads

Closed - 2200 ohms
Open - 3500 ohms

Which all seems fine. What else can I do to sort out the slightly rich running and choking up on low revs?

O2 sensor test?

[Speedtouch]

Are you sure on those figures? Being a variable resistor/potentimeter/rheostat, it should have an initial value of near to 0 ohms, rising to whatever its final value is at the end of the track.

You may have inadvertently measured the air intake temperature sensor bit!

http://www.autolib.diakom.ru/CAR/BMW/19 ... /fig02.pdf

[sharky]

Mcbonio

Cannot comment on the O2 sensor as I do not have one.

My AFM readings though when I gently opened the air flap with my finger to the fully open went up and down on the ohm meter.

The first dip was just after the flap was opened it went from 2ohm down to 1.6 and then as I opened the flap gently further it shot back up to 2.3. It did this at a few points while gently pushing the flap with my finger to the fully open 3.5.

The dip in the reading as soon as the air flap was opened with my finger to me coincided with the stutter/choking I was getting from cold when the accelerator was slighty pressed to take the car just of idle.

The replacement AFM has cured this and it has no dips when I had it on the Ohm meter.

[redcar]

You can't test the AFM by finding the resistances.

You have to whip a voltage across the potentiomenter track, then measure consistancy in voltage at the arm when opening it.

[sharky]

redcar

Brianmoore said that as well but the bently manual and haynes manual give this as the test to perform.
The test you state is this as posted earlier

http://www.the944.com/afm.htm

All I can say is I followed the bently manual and haynes manual on how to test the AFM and this lead me to the fact the AFM was mullered and it was as the replacement has sorted the problem completely.

So I am happy after being down every other blind alley.

Oh and it is not running rich no more, even better.

[mcbonio]

Right so I've measured it wrong. Bugger I've just this second put the thing back in the dark lol.

I'll get it back out tomorrow and test again... bah

[mcbonio]

Ok so not sure what I've done to the AFM last night but it's cured the split second hesitant choke issue! Smooth as!!

Although it still smells rich, and my idle is still 500-600 but stable. So I'm debating now on an AFM adjustment, what is the procedure for leaning out the mix slightly with the AFM? I know the hex bolt outside controls co2 at idle so I won't be touching that.

The AFM has a big cog inside to lean/enrich mixture, how does this work?

[sharky]

The Idle screw on the AFM might need adjusting, left to lean out.

Also have a read of this

http://forum.roadfly.com/threads/667907 ... es-it-have

[Brianmoooore]

Both of these adjustments are pre set at the factory and should never need touching. If adjusting either of them produces an improvement, then you are confirming that there is something else wrong with your engine.
If these adjustments are made, and at a later date the real underlying problem is fixed, either deliberately or accidentally, then the engine will still not be running at its peak.
Don't fix one fault by masking it with another.