How should an M20 idle anyway?

[redfoxiii]

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?

[crappycoco]

I'm also interested in this. If anyone has a cold start clip up until it warms up - that would be great.

[redfoxiii]

I'm still hoping to find someone on the board to corroborate, but I spoke with a few of the older techs at work who had spent time working on E30's and they all agreed that M20's hiccough and stutter when they are idling properly.

One guy said "asking an M20 to not have a goofy idle is like asking it not to sweat oil from the gaskets. It's just part of the character of those engines."

[Dagamus(NM)]

My black e30 that just sold idled at 550rpm and is very solid. It had a misfire and was idling at 700 when it came back from getting headers installed. Took me a long time to sort that one. The screw on cap for the o2 sensor wasn't in all the way. I pulled it apart, sprayed a little contact cleaner for any crust that may have gotten in and tightened it all the way. All bad symptoms went away.

Not saying this is your issue, just what was the culprit in mine.

[Kershaw]

One guy said "asking an M20 to not have a goofy idle is like asking it not to sweat oil from the gaskets. It's just part of the character of those engines."

He's not wrong, but he's wrong.

There ARE m20s out there that have a rock steady 650rpm idle and that don't leak/seep/drip oil. They just live next to unicorns, that's why you don't see them.

[redfoxiii]

The screw on cap for the o2 sensor wasn't in all the way. I pulled it apart, sprayed a little contact cleaner for any crust that may have gotten in and tightened it all the way. All bad symptoms went away.

Forgot to mention mine just got a brand new Bosch o2 sensor.

[packratbimmer]

Is the "mmmmmmphutmmmmmphutphutmmmmmmmm" sound at the tail pipe? My dad taught me to listen to the exhaust for burnt valves back when I was 14.

"mmmmmmphutmmmmmphutphutmmmmmmmm" would be a great way to describe the sound I learned.

[IceWhite]

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 M20 idles exactly like this.

[Cabriolet]

all 100+ m20s i've worked on have had hiccups. there have been a few eta's with turner chips that a very very smooth but still hiccup occasionally. and most I engines i've owned and worked on hiccup once every 3-5 seconds.

[Brian7]

Sounds right on par with my M20 as well but this is the only one I've dealt with :p

[redfoxiii]

Is the "mmmmmmphutmmmmmphutphutmmmmmmmm" sound at the tail pipe? My dad taught me to listen to the exhaust for burnt valves back when I was 14.

"mmmmmmphutmmmmmphutphutmmmmmmmm" would be a great way to describe the sound I learned.

Mine has Less than 3,000mi on a valve seat machining and head rebuild :-D

[Eskie]

Mine idles the same way. I have done everything I possibly can to try and make it different but I haven't been able to change it in any way. The only thing that drive me nuts is the slight drop and bog if the throttle is snapped off of idle.

Smoke checked for leaks 3 times now, 2 different AFMS, 2 different idle control valve, rewired the injector harness plug, checked EVERY sensor at least 3 times at the sensor and the ECU.

I'm starting to think that this is just a characteristic of this engine though..I know it couldn't be like that when it was BRAND new though.

[dnguyen1963]

"mmmmmmphukmmmmmphukphukmmmmmmmm" is the sound of my engine.

[15Michaeljoseph]

Sounds just like my idle as well. I grew up in this car and I always remember it sounding that way. The dips and hiccups are ALMOST predictable. It's controlled chaos, and honestly I like it a lot. Sounds a little bit lopey :)

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[M20]

It goes: mmmmmmphutmmmmmphutphutmmmmmmmm

This is pretty spot on

My engine sits right at 750 after warm up.

Mine tends to drop to around 500rpms sometimes