Funky Idle, drops to 500 then surges to 1k then evens back out at ~700

[Juevo]

So i bought this the other day and im just trying to pinpoint some solutions to an issue im having with my idle. Like the title states it will idle normally then randomly drop to 500 rpm like its about to cut off, then it surges to above 1000 and below 1300 rpm.

Vid of my idle

https://youtube.com/shorts/dbC1xKWw8Wo?feature=share

ive already got a bunch of parts coming for an engine refresh but im just wondering if this an engine issue or a fuel issue, or what the issue could be specifically.

Thanks in Advance my E30 pros

[e30davie]

At the very least tell us what engine it is..

[ZeKahr]

So i bought this the other day and im just trying to pinpoint some solutions to an issue im having with my idle. Like the title states it will idle normally then randomly drop to 500 rpm like its about to cut off, then it surges to above 1000 and below 1300 rpm.

Vid of my idle

https://youtube.com/shorts/dbC1xKWw8Wo?feature=share

ive already got a bunch of parts coming for an engine refresh but im just wondering if this an engine issue or a fuel issue, or what the issue could be specifically.

Thanks in Advance my E30 pros

Very likely a vacuum leak. Have a smoke test performed on the car before you throw parts at it.

[Juevo]

At the very least tell us what engine it is..

should be a m20b25 but i havent looked at the stamping on the head just yet but it revs out to 7000 so it should be a b25

[Juevo]

Very likely a vacuum leak. Have a smoke test performed on the car before you throw parts at it.

i wasnt planning to just throw parts at it and hope it works, i bought them to do a refresh like belts, injectors, and spark plug. but ill look into a smoke test to see if it has a vacuum leak too

[It's Soda Not Pop]

https://www.r3vlimited.com/board/forum/e30-technical-forums/e30-faq-and-diy/333798-diagnostics-tips-tricks-by-jim-levie-e30-jedi-master

[Juevo]

So I did some poking around and found that my intake boot has a pretty large crack in it, it didnt completely solve the idle, but it made the low rpm drivability a whole lot better. So ive got a new intake boot coming in, but if this doesnt solve the idle what other ideas do you guys have?

[CalE30]

Try cleaning the idle control valve. I was having some idle issues recently mainly when I push in the clutch to coast. Cleaned out the ICV and it cleared right up.