E36 M42 hitting a "wall" at 3,000 rpm? Bucking, hesitating, etc

[91e30181]

The first time I drove this car in rain (no chance of water ingestion), I couldnt get it to go above 3,000rpm.....kind of like hitting the rev limiter but a little more violent. Keep in mind the other 120 or so miles I had driven it prior (dry conditions) gave me no such issue and pulled clean to redline. I parked it, drove it again in the dry and now my "rev limiter" is still there but raised to 4k cold and 5k warm. Also, I now have a CEL at idle, but only when warm and the idle is sometimes higher than usual at up to 1500rpm's. CEL goes away as soon as I touch the gas pedal. I just bought this one and am about to embark on brakes, suspension and respray but now I need to clear this up first. I have no OBDI anything, so looking for anyone that has dealt with this before. All suggestions greatly appreciated!

[Tgoode318]

If its throwing a Cel that means you have stored codes. The best part about having an obd1 is you can do whats called a stomp test. here is an easy to follow vid and a great write up if you prefer reading step by step (like me) https://www.youtube.com/watch?v=5GlBsrOSefg  http://www.pelicanparts.com/bmw/techarticles/Mult-Code_Reading/Mult-Code_Reading.htm.
Once you have this code you should be able to tell whats wrong with your car, or at the very least narrow it down.

My opinion with out seeing your cel read-out, is that you are having a problem with a sensor(s). When the car is cold it runs on a set of stored parameter's in the computers DME. Once things have warmed up enough the computer goes to sensor readings and fine tunes your AFR (air to fuel ratio). A failed Crank Position Sensor and/or Camshaft sensor are likely culprits (another member on here recently had the same issue and fixed with a crank sensor). Having A blocked exhaust can also do what you said how ever you made the important distinction of it happening only when hot.

[91e30181]

Great place to start. Thanks!

[91e30181]

So I got a 1222, which is Oxygen Sensor Lean/Rich Detect (primary).......so that makes no sense, especially at idle only. As soon as I touch the gas it goes away, even a tiny tap. As soon as the revs drop back down it comes back in 2 seconds. But again, its the surging that Im more worried about. Im thinking its a vac leak and the unmetered air could be the problem?

[Tgoode318]

I should have seen this coming.. after telling you how helpful the montronic could be i should have known you would get the least helpful code lol. 1222 is a catch all that could be many different problems and really only helps narrow it down.. (It now sounds like a faulty O2 sensor possibly to me)
The First thing to do is to start with the cheapest things first though before throwing parts at it. Start by testing for vac leaks on the "mess under the intake" and the intake elbow. Take a can of carb cleaner or brake cleaner what ever you have on hand (i like carb cleaner) and with the engine running spray around all of your hoses listening for an increase in RPM (if you hear this you have a leak) Pay special attention to the area's around the intake bellow and the ICV unit. The intake bellow is one of the more common places to break because it actually flex's some and is the reason for the ribbed design instead of a smooth one. If no leaks are detected or you fix them and still have problems you should then check your Idle control Valve,  this can also be cheaply fixed by spraying carb cleaner into the unit and cleaning with a tooth brush (sometimes several times of cleaning/soaking are required) you can usually fix them if the plunger mechanism is stuck but sometimes a replacement is necessary.
 A quick way to check if its working is with the key turned one position (not on) a faint buzzing can be felt on the ICV by hand. A better way but requires some money (if you don't have a meter already) is to hook up an OHM meter to the icv and make sure the values are in proper spec. This Ohm meter is also how you can check the read outs on your O2 sensor to make sure its working properly. Lastly you can disconnect the icv and see if their are any changes in idle which would indicate a problem with the unit.
 If 1222 is the only stored CEL code then a crank position or cam position sensor is not your problem, much more likely is one of the things i posted above.
Good luck, and keep us posted with your results!
-TG

[91e30181]

Thanks again for the help. Ive had e36's with the m44 and e30's with the m42, but this is the first e36 with a m42. Is the "mess under the intake" the same as the e30 m42? Ive done that before, but these werent the symptoms. Id imagine I will be doing it regardless, but will definitely try the other things you advise. The reason I ask about the intake hoses is because last time I did it on my e30, I called the dealer and got them all. This time I called the dealer and they told me there are no such part numbers and it just regular rubber line. I remember it being specific hard and soft lines, but that was 8 years ago. And as far as that code goes, I bet its just the o2 sensor picking up a lean condition from a vac leak. Thank you once again!