Couple questions on the old m20

[ThatOneEuroE30]

So I got another e30 and it's a late model 325is this is my first experience with a real m20 cause on my euro spec it was a b20 and I ripped it out right away and shoved a m30 in so I don't really have a lot of knowledge on the m20 besides the basics. The car has already had the timing belt and such replaced I'm just wondering what I can do to make it run the best it can. I put some e3 plugs in it and that helped but it seems to idle a little high for me around 1200-1400 sometimes it may drop down to around 1000-1100 what could I do to improve that or is this the normal m20 idle? My b20 had a idle issue so it always ran at like 1700. Also what's the best oil for these things? I got some high mileage valvoline 5-20

[crappycoco]

idle:
- smoke test the car, locate leaks.
- buy new vacuum hoses and replace as needed (in 80% of all cases thats the problem).
- check ICV (remove, inspect, clean - if it doesnt click when you move it its gunked up)
- check AFM (a guy on the forums refurbishes them for $150, or you can get a low mileage replacement - there is a surface inside that wears out.)
- Replace Coolant temperature sensor
- Check voltage regulator (even if it doesn't help the idle, its good to replace it, since they designed it to wear through use)

After this it gets complicated, I would try those first =) Next steps involve replacing intake manifold and throttle body seals. =)

Hope this helps.
And 1400 is NOT a normal idle, I would say its about 2x the normal idle.


AFAIK, you should run 10W40 (cold weather) or 20W50 (warm weather) in these engines. 5W20 is way too low. But thats just me, maybe some of the guys will know for sure =)

[Sea Aych]

^yup, i run 10W40 in the (canadian) winter, and 20W50 for when the temps go back above 10C

*edit: regular, not synthetic

[ThatOneEuroE30]

These motors dont use synthetic?

[mitchlikesbikes]

you can use either one really. mine has been running pretty nice on mobil1 15-50 synthetic. it's available at walmart now too so it's cheap/easy to get

[ThatOneEuroE30]

I just put the 5-20 in yesterday so I may go get so castrol gtx 20-50 cenventional. It's only 20 for 5 quarts at walmart.

[dnguyen1963]

The use of synthetic oil can be iffy in these engines because it contains higher amount of detergent. Many users have experienced oil leaks after switching over to synthetic, some not. The car will run just fine with either oil, but if you are not lucky then you will have to deal with a leaky engine.