M20B20 rev drop when starting

[ciocc]

Hello, I've been having this problem for a while but have been somewhat avoiding dealing with it
Upon ignition, the revs drop below 500 rpms just before surging back up again. On a cold start it usually doesn't start on the first turn, I usually either have to turn it a few times or turn the starter until it starts to pick up. I filmed a video of this problem today (attached below), but it was on a warm engine. I had one instance where the car wouldn't start at all and had to be towed to start. What could be the culprit?
Also i'm getting pretty poor mileage, ~15 l/100km urban. Apart from the start issues and increased consumption, the car seems to be running okay, the head was rebuilt ~4000 km ago, recently repaired starter, fresh plugs and wires, recent oil change, maf is okay, o2 sensor works fine.

https://www.youtube.com/watch?v=P6Z2fVsU0QA

[ciocc]

Anyone?

[MrBurgundy]

Check the coolant temp sensor, icv vane and the afm

[ciocc]

Check the coolant temp sensor, icv vane and the afm

I had it hooked up to a diagnostic computer, the coolant sensor seemed okay, there was an afm error a while ago but i cleaned it with a maf cleaner and it seemed okay. I also cleaned the icv with carb cleaner a while ago. Is there another way to test the maf?

[MrBurgundy]

How does it drive while accelerating? is this just and idle problem, or is the car acting up across the rev range?

[ciocc]

How does it drive while accelerating? is this just and idle problem, or is the car acting up across the rev range?

When I first bought the car, the acceleration was waaay sluggish. Then after some engine repairs and a new clutch it feels better. Still accelerates kind of slow, but it certainly got better. I don't really have anything to compare it with, but everyone is saying that the b20 is slow, so my guess is that it might be normal.

Oh and the revs only drop upon ignition

[MrBurgundy]

Hmmm, I was diagnosing a problem on my car. I swapped the AFM with one I had laying around and I had a very similar problem. The car would idle very low, like yours. I'm not sure how to test for that specific problem on the afm. Maybe someone else will chime in. If not, since you had a trouble code for it, i would look for one to swap to make sure.

[ciocc]

Hmmm, I was diagnosing a problem on my car. I swapped the AFM with one I had laying around and I had a very similar problem. The car would idle very low, like yours. I'm not sure how to test for that specific problem on the afm. Maybe someone else will chime in. If not, since you had a trouble code for it, i would look for one to swap to make sure.

I will try to look for one. Thank you for your answers

[ciocc]

Upon further reading, I suspect a faulty o2 sensor. Could these symptoms be caused by a faulty sensor?

[jeffnhiscars]

O2 sensor doesn't kick in til the car warms up