My M42 (in an E36 318iS) has started to act up.Previously it started fine when cold (leaving it overnight). But hot starts needed a few well-timed taps to the accelerator, otherwise the revs will come come down and the car will stall. Once the revs stopped bouncing, the car will idle fine. Once it settles down, the car drives fine.Now on cold starts, the revs MIGHT bounce a little (once? twice) after starting, but won't stall. However, on hot starts, I consistently can't get the car to idle unless I rev it hard (past 3K rpm), then the idle will stabilise. Sometimes, even if I rev past 3K, it still won't idle and I got to do it two or three times. Car drives fine once I can get it to idle.What could be the cause of this hot start problem? Fuel pressure regulator? O2 sensor? I can get about 500km on a full tank and like I said, the car drives fine. It's just this hot start problem that's bugging me.Any help appreciated! Thanks!!
(Another?) hot start problem
- Thread starter guinness
- Start date
-
Click here to become an Official Member of BMW Club Malaysia Download Form
saintdagon
Club Guest
- Joined
- Mar 26, 2009
- Messages
- 91
- Points
- 0
clean your idle control valve
anaksarawak
Official Member
- Joined
- Jan 20, 2007
- Messages
- 4,154
- Points
- 0
Try this...
Change the spark plugs and ensure you dont over fill your engine oil ..just below max is good!
It work for me.
Change the spark plugs and ensure you dont over fill your engine oil ..just below max is good!
It work for me.
Guna;458583 said:
I did have a look for brittle looking hoses and couldn't find any. That said, the stuff below the intake manifold is a little out of sight but my thought's the same - that if there was a vacuum leak, wouldn't the poor idle be there all the time?
geoffreylee;458587 said:
thanks for the suggestion but I doubt this is it. Plugs aren't that old and have changed/checked the engine oil a month ago. The car idles fine normally and on cold starts, it starts fine.
I'm thinking more along the lines of a faulty sensor - what sensors 'kick in' during a warm start? O2? Throttle position sensor?
Guna;458628 said:
erm, no problems with idling when driving etc and from a cold start, also no probs.
the problem is from a warm start. right after a warm start, it can't really hold idle - that might be for 15 seconds? sometimes maybe half a minute? I gotta keep tapping the gas pedal and revving it up to 3K or so sometimes helps to prevent it from dying. but after that, it's fine. once the idle settles down, it's all back to normal and pretty rock steady. tks!
I think I found the problem. I suspect its the fuel pressure regulator.
When I disconnect the vacuum hose leading to it, it seems to start fine. When I connect it back, it gives me that hot start problem.
What does the vacuum hose exactly control on the fuel pressure regulator? Is it all right to leave it 'unplugged' from the vacuum hose until I replace the fuel pressure regulator? Hoping its an easy DIY job.
When I disconnect the vacuum hose leading to it, it seems to start fine. When I connect it back, it gives me that hot start problem.
What does the vacuum hose exactly control on the fuel pressure regulator? Is it all right to leave it 'unplugged' from the vacuum hose until I replace the fuel pressure regulator? Hoping its an easy DIY job.
champion;459290 said:
It's a vacuum hose for sure and not a fuel hose - the other end goes in to the throttle body.
I just read that sometimes when the FPR is damaged, it might leak some fuel so you're right in that maybe its not that good an idea to leave it unplugged while running.
What I'd like to find out is if its really the FPR that's faulty and if my 'unplugging vacuum hose test' can confirm that the FPR is faulty. It seems like an expensive small part! Tks.
according to bentley service manual, a cracked or leaking vacuum hose would caused eractic idling speed.
Since you dont have leaking hose, then the regulator might be a problem.
BTW, Removing the vacuum hose would increase the fuel pressure at the fuel rail or distributor.
Since the idling speeding is constant when you removed the vacuum hose, more fuel at higher pressure is available to keep the speed constant. i.e fuel starvation. Chances is that the fuel regulator is faulty in the first place.
Another thing to consider is the fuel pump. If the fuel pump is not functioning properly, the fuel pressure at the fuel rail is also reduced causing erractic speed.
As mentioned earlier, the fuel pressure is also affected when the fuel filter is chocked.
If you want to remove the vacuum hose to the fuel regulator, make sure the end to the throttle body is sealed up with a plug.
I dont think the fuel regulator is an expensive thing to change.
good luck
Since you dont have leaking hose, then the regulator might be a problem.
BTW, Removing the vacuum hose would increase the fuel pressure at the fuel rail or distributor.
Since the idling speeding is constant when you removed the vacuum hose, more fuel at higher pressure is available to keep the speed constant. i.e fuel starvation. Chances is that the fuel regulator is faulty in the first place.
Another thing to consider is the fuel pump. If the fuel pump is not functioning properly, the fuel pressure at the fuel rail is also reduced causing erractic speed.
As mentioned earlier, the fuel pressure is also affected when the fuel filter is chocked.
If you want to remove the vacuum hose to the fuel regulator, make sure the end to the throttle body is sealed up with a plug.
I dont think the fuel regulator is an expensive thing to change.
good luck
jarance;459307 said:
Thanks Jarance. I don't have an erratic idling speed issue - its more like a it-won't-idle-on-warm-start problem, but once it idles, its rock solid.
After checking up on the Bentley too - I have to agree your analysis is spot on with what I've just concluded.
It seems like the fuel pressure regulator is not holding enough pressure in the fuel system on warm starts - hence when I remove the vacuum hose and the pressure increases, the warm start problem seems to go away. Somehow, it seems to regulate the pressure fine when its cold though.
As mentioned, once I can get the car to idle, it seems to drive fine hence I'm not suspecting the fuel pump or the fuel filter YET as I think if the fuel pump or the filter is problematic, I should be getting more consistent problems (cold or hot). Will likely change the fuel pressure regulator first and see how that goes.
Thanks all for the help - will report back once the FPR is replaced.
Changed my fuel pressure regulator and the problem is fixed!
The FPR comes with the O rings. Simple DIY. Just remove the 8mm nut to loosen the FPR holder/frame, then slowly twist and pull out the FPR. It was rather tight but since my FPR was screwed, I did not need to be too gentle with it and held it with a pair of vise grips - did the job for me. Be warned that the fuel system is under pressure so fuel WILL spray so best to cover the FPR with a rag and please protect your eyes when you loosen it. Installing the new one is a simple matter of reversing the procedure.
The FPR comes with the O rings. Simple DIY. Just remove the 8mm nut to loosen the FPR holder/frame, then slowly twist and pull out the FPR. It was rather tight but since my FPR was screwed, I did not need to be too gentle with it and held it with a pair of vise grips - did the job for me. Be warned that the fuel system is under pressure so fuel WILL spray so best to cover the FPR with a rag and please protect your eyes when you loosen it. Installing the new one is a simple matter of reversing the procedure.
