Rough Idle (sometimes)

[HappyE21]

I started my car about an hour ago and it died about 3 or 4 times before I could actually get it running, once it was running the RPMs dropped to around 700-800 when it is usually at around 1100 (manual trans), the idle was also pretty rough constantly fluctuating about 100-200 RPM. It hasn't idled like that since before I did an overhaul on the fuel system (cleaned tanks, all new lines.) After I finished the fuel system it started perfectly for like a week, until tonight. I had drove the car about 3 hours prior to this with no issues starting or idling, and the engine was still moderately warm.

There isn't a single mechanic in my area that wants to work on my car so I was hoping a BMW expert in here could help me out. I'm thinking It could be a vacuum leak, I don't think any vacuum hoses have been replaced on this thing in quite some time. I have also read that I should adjust my air fuel mixture after something like the fuel overhaul I did. I put the multimeter on the o2 sensor and it read 0.92 volts (I think its supposed to read .45 volts) so I defiantly have some adjustments to make there, I just have no clue how I'm supposed to turn that little 3mm hex screw on the fuel distributor. Possibly a valve adjustment and ignition timing adjustment may help the problem as well? Idk I'm still new to cars, let me know what you guys think, yall know the best

[DavidF]

For the mixture: I have seen others fabricate a tool to be able to reach straight down into the hole for the mixture screw. Take a regular 3mm hex wrench, cut of the short bend so you have a straight tool. Weld it to the tip of an old screw driver long enough to reach through the manifold.

The mixture hole plug is probably long gone.

[Mike2002]

Find someone with a smoke machine to find the vacuum leak.

[HappyE21]

For the mixture: I have seen others fabricate a tool to be able to reach straight down into the hole for the mixture screw. Take a regular 3mm hex wrench, cut of the short bend so you have a straight tool. Weld it to the tip of an old screw driver long enough to reach through the manifold.

The mixture hole plug is probably long gone.

I think I've seen a video on youtube of someone doing what you described, I'll call my buddy and see if i can use his welder. The hole plug is gone, does that cause vacuum leaks?

[DavidF]

No, the hole allows air to enter the air box in front of the metering flap, so the small amount of air is being measured. But, the hole will allow dust and moisture (i.e. if washing down the engine) to enter the air chamber.

I made my own smoke machine: A cheap fluid transfer pump, nitrile gloves and a cigar. Cut the tip off one finger of glove and insert/tape the pump discharge hose into the finger hole. The wrist end of the glove goes over the throttle valve (or wherever). Light a cigar and insert it into the suction side of the pump. Start pumping cigar smoke into the engine and look where it escapes. Helps to hold the throttle plate open.

[Clio320i]

+1 on holding the throttle plate open and you'll also want to plug the mixture hole because smoke will come out there. I wasn't brave enough to try to make a smoke machine so I ponied up about $80 and got one of these and used it with a bike pump as well as their intake boot cone adapter. The smoke machine I got didn't come with their smoke fluid, so I used mineral oil.

I have never messed with ignition timing so I have no meaningful input there, but sure, do a valve adjustment. It probably won't affect your idle though, unless the valve cover gasket itself is leaking, and you'll replace that when you do the valve adjustment anyway. I agree with you that it's a vacuum leak - probably some rubber thing just cracked or something like that.

[mxl556]

Before messing with the mixture, I'd make sure the red plug underneath the intake manifold is not missing , it sometimes falls off and creates a huge vacuum leak. Also I'd try disconnecting the 02 sensor and see how it affects the idle.

[HappyE21]

Thanks for all the info guys! I've been pretty busy so I will try running a smoke test tomorrow. I will post an update once I do so!

[HappyE21]

So I know that there is a vacuum leak, didn't do a smoke test but you can just hear it whistle when i put the foot down a bit. I started taking my engine apart today (m10b18) and found all sorts of hoses that where pretty questionable. I ran a compression test and all cylinders where between 148-152 psi, very happy with that. Also found that 2 of the coolant lines to the throttle body where completely plugged up, and the hose made a crunching noise when i bent it, ill be replacing those for sure.

My next question is how far should i go with this, i already have pretty much everything besides the head and block taken apart. Is it much harder to just pull the head and put a fresh head gasket in there for some preventative maintenance. I'm also looking into getting some more power out of the m10, I've read that putting in a 292 cam can be a lot of fun in the higher revs, but painful in traffic. Or i hear people talk about a mega squirt conversion.. or both? not sure where to go with this, this is just a project car so im in no rush to get this done quickly, but I'm also in high school and work only brings in about $250 a week. You guys let me know your ideas!

[cgifool]

If the compression is good and you don't get blue smoke on accel or decel, I would leave the head and head gasket alone (for now)...

Start with replacing the vacuum, water, and fuel lines, get what you have working well, while you decide on longer term plans.

JRCook posted a good list of things you can do on a budget:

https://www.bimmerforums.com/forum/s...0#post18900870