Running problems help please!

[Danny_jb]

Hi, I have a BMW 323i, I cleaned the throttle body as the car would not idle properly when holding it on the clutch. After the air pipe was back on the car ran perfectly and the problem was gone. After running for a few minuites the car backfired and now wont idle at all with the air flow plugged in (already replaced today) but with the airflow off the revs bounce and the car tries to cut out unless the throttle is pressed then the engine run's smoothly with a slight clicking sound. I was thinking maybe a vacuum pipe was blown off the manifold or had split. I would really appreciate any help.

p.s The car has been running with a faulty Lambda sensor for a long time and has also had the ECU remmaped.

Thanks

 

[pgarner]

is it an electronic throttle body or a cable one ?
if its electronic it may need aligned

 

[Danny_jb]

Cable throttle body checked the cable and its fine. Thanks for your reply im just hoping its nothing expensive!

 

[obi_waynne]

Have you inspected the afm after the backfire? Is the AFM plugged in the right way round?

 

[Danny_jb]

Yes I have tried a new AFM aswell which only fits one way, I have now found a hole in the pipe going to the idle control valve, when I blocked the hole the car began to run better! so I think the backfire blew a hole in it do you think the hole could be the complete problem or is there likely to be other problem once I have replaced the pipe?

Thanks for your reply.

 

[Danny_jb]

Also I forgot to mention when the car was running tonight it idled but it started to pop and bang a little I was thinking this could be because of the hole like when you run the car without an air filter. Hoping theres no engine damage!!!

Thanks again

 

[pgarner]

if this pipe is a vacuum line then yeah this could be causing issues.

 

[obi_waynne]

Wrap a bit of elephant tape round it and see how you get on. That will probably sort it.

 

[Danny_jb]

Tried that today also found a broken vacuum pipe to the fuel pressure regulator on the fuel rail sadly no diffrence and the car backfired again! I dont know what has happend but its not acutally my car Im starting to worry what could be wrong what could be causing the backfire for a start? I would be very greatful for any suggetions!

so far I have

Cleaned the throttle body (before the backfire, wouldn't idle when held on clutch)
Changed the airflow meter
Checked air/vaccum hoses
Checked for air leaks

Is there any way me cleaning the throttle body with carb cleaner could have damaged something causing it to backfire? Or is the any chance of ECU/Engine damage?

Thanks again for all your help!

 

[Loz]

Is a back fire when the unburnt fuel enters the exhaust?

 

[Danny_jb]

The backfire is through the intake not the exaust i dont have a clue why as i cant find any leaks! but unburnt fuel in the exaust would ignite in the cat but sadly its not so simple on this car as running to rich

 

[pgarner]

theres a point loz

have you checked the plugs / leads.
the fuel pressure line might have been causing it as the vac controls the flow

 

[pgarner]

sorry danny you replied just before e

 

[Danny_jb]

It has direct coil packs to the plugs no leads but it runs perfectly when at fast idle, Im starting to wonder if the idle control valve is faulty due to the first backfire but im not sure no lights show but it could be still within the limits of the ECU? Also there is something on the manifold which i had to remove to get to the split vacuum pipe, it is like a throttle butterfly in the inlet manifold but it is plastic and right at the top im not sure what this is and so not sure if it could cause any problems?

Thanks again

 

[Loz]

Isn't that part of the idle control valve. On my engine I think there's a stepper motor involved that needs calibrating. Have you disconnected the battery recently?

 

[Danny_jb]

Im not sure to be honest but I suppose it could be part of the same system, I am going to try scan the ECU tomorrow and see where that gets me, the battery has not been disconnected but mayb the backfire caused them to go out of sync?

Thanks for all your help I appreciate it as I am struggling with this problem!

 

[pgarner]

Loz the stepper motor is on the thottle body on electronic throttles , as its cable operated its not there.

 

[Danny_jb]

Ive scanned the ECU now which has given me the fault of the MAF again. I have been told sometimes genuine parts wil work but cheaper ones wont as this is a cheap part do you think this could be a problem? Also would a the MAF cause a backfire I was thinking because of the incorrect fuel air mixture. I was also thinking of calling the auto electricion I think the osciliscope would be very helpful?

 

[pgarner]

could have been a faulty maf anyway mate, just cause it was new doesnt mean it will work.
not sure about it causing the back ire but the burst pipes may have been the original cause

 

[Danny_jb]

Yes i think im just going to get the electition to try test the system to be safe and they wont take the maf sensor back anyway they say its electrical tough i already bought it... so before spending 180 on a new one i think i should be sure.

Thanks again for your reply

 

[Sid447]

A couple of things to mention here,

The mass airflow sensor won't cause backfires and erratic idle. But you must find a genuine o.e. replacement as the maf calibration in them is critical to part-throttle and WOT parameters.
What does cause backfiring and un-even idle is a faulty O2 sensor. So this should be replaced.
Checking the intake system also for air leaks and giving the throttle plate and IAC motor (Idle Air Control) a clean with for example kerosene will help with having a stable idle.
(Just remove the IAC motor and clean it with a paint-brush soaked in kero).

An air leak on the intake system won't cause back-firing at low rpm either. It would cause hesitation under acceleration and coughing or surging at cruise speed though. As the fuel mixture would tend to be too weak at the higher speed.

Un-plugging the mass a-flow sensor causes the ECM to drop into back-up mode which means it runs in Speed Density Mode This does no harm whatsoever, it just means you may run a little down on power.
Un-plugging it would also cause an ECL (Engine Check Light) to come on though.

I would suggest getting the correct o.e. maf-sensor and also replace the O2 (lambda) sensor. Assuming the intake system is now free of air leaks

 

[mattself]

i have a e36 316i 1.8 engine, had exactly the same problem, engine wont idle, backfiring/misfiring, scanned it with diagnostic computer and error codes pointed to AFM, replaced it and it seems to have fixed it, i at first thought plugs/leads but was suprised to see AFM appear. Hope this helps.. Matt