High idle

#1

Hi Guys, I would love to hear you comments to this issue here I have.
For some time now, suddenly the idle would jump up to around 2000RPM, then after a while it would jump right back to normal.
I know that high idle is normally an airleak but in this case the problem is 100% ON/OFF, sometimes bad sometimes good with nowhere in between, to me this does not appear like an air leak but something electrical. Naturally I have testet the idle valve and it appears fine but again with an ON/OFF problem, I could have been testing it while good, I cannot be sure. I have ohmed a lot of connection, sensors etc up to the ECU and although not everything, I have not found any errors. For over ½ year the problem has become more and more frequent and now it is mostly in the bad state, still jumps down to normal now and then. I have disconnected the o2 sensor now (dont have a cat) and according to haynes this will cause the ECU to run in open loop mode which I would expect will work rather well, yet the problem is the same. My idea is that its better to disconnect the o2 sensor while troubleshooting and when every thing is great then attach it as the final thing, as open loop mode must be easier for debugging,- agree? The oilcap I read could be causing false air, funny thing is if I open it the RPM drops a lot,- ehhh??? how does that make sense? I have a Motronic 1.3 as well as an 1.1 and the problem is the same so I rule out the ECU. It does not matter if the engine is cold or hot, it can happen in both cases. I am a newbie in E30 so I’d really appreciate anyones ideas about this.
Mark

#2

Check the throttle position switch?

#3

Every motor I built I removed the ICV and replaced it with an idle speed of about 1300rpm cold, which was 15-1600rpm warm. You don’t need to go any lower.

#4

Thanks, but none of the above. I forgot to say my engine is a 325. Does anybody drive without the O2 sensor as I now do, how does this work for you? What happens when you open the oil filler cap at idle?