M42 Idle Screw

[timmy.chisholm]

Good day,
     I have been looking around on forums and I have been coming across posts that say you cannot adjust the idle on an m42 engine via the idle adjustment screw on the throttle body. They say the computer automatically compensates and brings your idle back down. Troubleshooting my roughish idle on my engine I can adjust the idle using that screw... is this a sign that the ICV is not working properly? Any one have thoughts on this?

Thanks,
      Tim


1991 BMW 318i    M42 Engine

[bmwman91]

Yeah you really are not supposed to mess with the screw on a properly functioning engine. The throttle should be closed when at idle. I think that it is actually a mechanical stop for the linkage, not an idle adjustment.

Rough idle is almost always one of two things (often both):
1) Vacuum leak
2) Gummed up idle control valve

The ICV is easy to clean. Buy a can or two of carb cleaner and blast the ICV out. The little door should move freely when you shake the ICV around by hand. I let mine soak in a cup of rubbing alcohol for a few hours, totally submerged. THen I poured it our and ran more alcohol through it. Just make sure to let it dry out for 24 hours.

Vacuum leaks are a little more of a pain, but they aren't too tough to track down.

[timmy.chisholm]

Thanks for the advise!
I don't think I have a vacuum leak since I replaced the MAF to TB pipe and the line off that that goes to the ICV. As well as the TB to Head Cover line. I think those are the only vacuum lines... I may still spray carb cleaner over everything to see if there is a pick up in idle to see if there is a leak.
   As for the ICV, I already cleaned it out, but I'm going to try to clean it out again on your suggestion to submerge in rubbing alcohol. If not, i'm going try another ICV.

Thanks

[timmy.chisholm]

After changing the ICV and changing the vacuum lines, still no difference. Also changed the MAF. I'm back to the thought of throwing a screw in there to make sure the idle cannot drop. Oh well...

[Gabs]

Other things that may cause rough Idle, The actual MAF being faulty/damaged, O2 Sensor,  leaky valve cover gasket, camshaft position sensor. On the more extreme side of things, bad rings/low compression on high mileage engine could also cause a rough idle.

Edit: Just noticed you said you tried a new maf, so scratch that being faulty/damaged.

[timmy.chisholm]

Is there any easy way to check leaky valve cover gasket? That topic also made me think it may be something to do with leaky valves because my car does not accelerate the way i think it should (Considering my rear diff has my gearset such that I will be going 50 kph at 2000 RPM in 4th gear, which i guess is a pretty high torque setting). I ordered a compression testing kit online and I'll check if its something with the valves or rings once it comes in. Thanks for the places to look Gabskee, I was hoping my ECU could tell me about the CPS or the O2 Sensor, but unfortunately it's not giving any info with the "stomp test", I think my maybe my check engine light is burnt out. Well, that's enough of a rant for now.