E36 325i - unstable idle, engine runs bad...

[brka]

Hi,

Having some problems with my 325, first of all after the engine warms up idle becomes unstable, it cycles between 500-1200 rpms, first few minutes after I start the car it looks ok but as soon as it warms up a bit it becomes unstable. Second, the engine is a bit sluggish, when starting from a stop it almost dies then picks up, also I noticed that the exhaust is black as a chimney. MPG gauge is also going wild... Now I check the ICV, hoses, DME is not wet, what else to check, could it be a O2 sensor ?

Thanks.

[kocio67]

When engine is cold (temperature up to 70C- around 170F ) engine's management is using default parameters and information from O2 sensor is not used by computer.
Once water is warm, O2 sensor information is important, so probably this is your case.
You should check if you have any ECU errors
check Pelican site, they have info how to do it.

[brka]

Thanks for the info, will check the O2 sensor. BTW I already tried to check the ECU codes with the 5xpedal procedure but to no avail.

[golden]

the temp sender is your first route of investigation. Same thing happened on my car and the temp sender on top of the thermo (?) was sending wrong info. Bad,..and even making my cat converter stink.

[brka]

Hm, that's a good point, as a matter of fact there is a strange smell form the cat. Can you provide me with some detail where is the temp sensor located ? And maybe even more
important, how the test if it's sending wrong readings ?

Thanks !

[golden]

I have no idea how to test but I bought my car this way for 1100 dollars and just had a feeling it was a sensor of sorts. Was right ,...and haven't given it a thought since the mechanic fixed it. All I can say is Bentley Manual available everywhere will give the correct parameters for most all technical questions. Those Haynes manuals most useful to collect oil leaks

[Jared at Pelican Parts]

Originally posted by brka
Hi,

Having some problems with my 325, first of all after the engine warms up idle becomes unstable, it cycles between 500-1200 rpms, first few minutes after I start the car it looks ok but as soon as it warms up a bit it becomes unstable. Second, the engine is a bit sluggish, when starting from a stop it almost dies then picks up, also I noticed that the exhaust is black as a chimney. MPG gauge is also going wild... Now I check the ICV, hoses, DME is not wet, what else to check, could it be a O2 sensor ?

Thanks.

You have a vacuum leak somewhere....

[brka]

Originally posted by Jared at Pelican Parts
You have a vacuum leak somewhere....

Well, I already check the hoses bit will double check it. What was the best way to do that ? Spray them with soap&water mix ? Anyway still waiting for the O2 sensor, the car has ~80000 miles on it so it can't do any harm to change it. I will post the results.

[golden]

i thought this problem was intermittent,.....if that's the case the temp sensor is telling the computer it's below freezing outside and hence the dark black soot "chimney smoke" from the exhaust with no power. I'd try the 13 dollar temp sensor long before the 100 dollar O2 sensor. The o2 sensors are a lot more durable than they let on.

[Jared at Pelican Parts]

temp sensor is also a good idea

[brka]

Just wanted to share the results with the rest of the people reading this forum. I had some free time on my hands today so I said to myself, what the hell, lets see what we can see. First of all I unplugged all the conectors that were reachable without removing the intake manifold. This means, ICV, temp sensor, coolant temp sensor, all the hoses. I found that one of the hoses that goes into the injector fuel rod is leeking gas. Checked the O2 sensor, and found that some insulation on the wire is missing so I wrepped it with some insulation tape. Removed the coils and spark plugs, they seem ok, a bit black but I suppose thats because of too much fuel in the mixture ? So after I've put everthing back togeather I crossed my fingers and started the car. And......well I am glad I didn't go out an bought a new O2 sensor because now everything seems to be ok. Idle is steday at around 700 rpms, car runs great, no more black smoke. What was the problem ? I have no idea and that's bothering me a bit. I just hope it will last. Anyway, thanks to all the people that responded to my questions.

[golden]

I still think it is going to be the temp sensor because my car would behave and I used to think just because it was rainy ,...foggy,..or I just didn't turn the key right it would act up with the racing up and down idle and then the no power sooty smoke from my "diesel" It is very intermittent

[brka]

Originally posted by golden
I still think it is going to be the temp sensor because my car would behave and I used to think just because it was rainy ,...foggy,..or I just didn't turn the key right it would act up with the racing up and down idle and then the no power sooty smoke from my "diesel" It is very intermittent

And ofcourse the saga continues, today the same thing, and it was running ok for almost two days. Well first I'll try the temp sensor. Which sensor are we talking about ? Is it the one on the engine block (next to the coolant temp sensor) ?

Thanks !

[brka]

Just to add some more info, checked the sensors (temp sensor and coolant temp sensor). When engine is cold both have resistance around 1500 ohms and the resistance is decreasing as engine warms up so I guess they are ok. Now the idle is surging between 700-800 rpms. Now I am lost and frustrated, I just hope that this is not a faulty DME.

[brka]

Just to close this issue, after taking everything apart (again) including the injectors, and the intake manifold, I found that a vacuum hose conecting the fuel pressure regulator and the intake manifold is broken. I guess it was bareley holding and in a process of me removng the fuel rail it just broke in half. So Jared was right all the time, this was a vacuum leak plus the regulator not working properly because of the cracked hose. Anyway after I've put everything back togeather the car is running great (for a week now) idle is rock solid, no more hesitation from the engine...