How should an M20 idle anyway?

[cheffy30]

I see tons of posts about rough idles and idle problems - but none that seem to describe what a good idle should be.

My engine sits right at 750 after warm up. No vacuum leaks (checked with a smoke machine), ICV is super clean internally and moves freely, new(ish) MAF.

It goes: mmmmmmphutmmmmmphutphutmmmmmmmm

Sounds like misfires or dead misses. The idle does not change or drop.

The shop foreman at my work (a BMW dealership) described M20 idles as "lumpy" when they were operating correctly, and my 90 325is would certainly qualify as that, I think.

Is this normal?

i just replaced my timing belt, water pump, did a valve job, replaced wires, plugs and rotor, oil change, air filter and fuel filter...

it still idles a little bumpy right at 750rpm...
when i step on the gas it takes off like a rocket... engine winds up beautifully... love the m20... been like that since i bought it 14 years ago...
no oil leaks.

drive it hard. wash it. maintain it... has 241k on the engine... i see no foreseeable issues...

[cheffy30]

I see tons of posts about rough idles and idle problems - but none that seem to describe what a good idle should be.

My engine sits right at 750 after warm up. No vacuum leaks (checked with a smoke machine), ICV is super clean internally and moves freely, new(ish) MAF.

It goes: mmmmmmphutmmmmmphutphutmmmmmmmm

Sounds like misfires or dead misses. The idle does not change or drop.

The shop foreman at my work (a BMW dealership) described M20 idles as "lumpy" when they were operating correctly, and my 90 325is would certainly qualify as that, I think.

Is this normal?

my 1990 325i m20 is always rumbling a little.... its been that way forever...
even after a valve job, timing belt, water pump, points, plugs, wires and an oil change... if its not like that then something is wrong...

[Mahalaleel]

Mine sounds like a sewing machine and my fuel pump whines. I'm planning a valve adjustment, new fuel rail and M50 injectors when they arrive, all at once. That'll be in January though because I'm leaving my poor E30 alone for a month while I'm in DC.

[redfoxiii]

Dead (?) thread revival:

https://youtu.be/9za8Es4KxoI

My car idling.

[15Michaeljoseph]

Dead (?) thread revival:

https://youtu.be/9za8Es4KxoI

My car idling.

Sounds pretty good to me. You might want to get a cover for that afm though, that's not supposed to be open to the elements

Sent from my XT1064 using Tapatalk

[cheffy30]

mine is lumpy as well, has always sounded like this... sounds great to me... what do i know...
when i step on the gas it purrs though...

[redfoxiii]

It has a cover, it's just loose enough to peel off. I'd glue it back down if I noticed any dust incursion.

[franklinmomo]

My M20 seems to be a little bit more than just lumpy or rough. It'll idle okay for a second and then it sounds like it misses for a few seconds, then it'll try and idle normal for another second before doing the same thing over. I just did the head gasket, it doesn't seem to be leaking but I still need to do a compression test.

https://youtu.be/oV_tVuA3SBg