Engine misses for 5 seconds on cold start

[Earendil]

This one has baffled me. On cold starts (after sitting overnight) the car spits and sputters for the first 3-6 seconds, and then clears up and idles smooth and on mark.

Car didn't start doing this until a few weeks ago.

Due to what gets used and what changes that fast, I don't think it's the O2 Sensor (not used until warm) or the Coolant sensor (Temp doesn't change in 3 seconds).

I'd say I had leaky injectors that caused a few poor firings until the cylinders were clear, but there is no increased smell of gas, and the injectors are freshly cleaned and flow tested as of 7 months ago. It also doesn't have trouble starting up, maybe an extra crank, but nothing that causes even a split second fear that it won't start.

Thoughts?

[Andy.B]

What engine and motronic version?

[Earendil]

What engine and motronic version?

Whoops, I should probably state that more clearly :)

M20B25
Motronics 1.3
173 ECU

[Andy.B]

The first thing that comes to mind after leaking injectors is coolant/oil leaking into cylinder from a bad hg or crack, very poor compression, or air leaks.

[Earendil]

The first thing that comes to mind after leaking injectors is coolant/oil leaking into cylinder from a bad hg or crack, very poor compression, or air leaks.

don't say that! :shock:

That actually did cross my mind... but it's running so well and the HG is only 2 years old. No other signs of HG trouble either... of course that doesn't mean anything. I have been missing a little bit of coolant recently (longer than the start issue), but I also sprung a small leak from my waterpump and I was hoping that was where all the water vanishing too. I'm not blowing steam out the tail pipe yet either.

An air leak would cause a poor idle, and wouldn't clear within a few seconds afaik. I think I can dismiss that one safely.

I've never dealt with bad HG issues. If I pull a plug and shove a small cleaning brush into the cylinder will it come out wet/oily if that's the issue? I'm not sure how much of a leak it would take to cause an issue like this.

[russc]

Got a friend with an e30? Try swapping in a different MAF. Maybe yours is gunked up.

[Earendil]

Got a friend with an e30? Try swapping in a different MAF. Maybe yours is gunked up.

Also less likely, as my AFM (no MAF in these) is also freshly rebuilt as of a few months ago. I've never heard of an AFM fixing its self after a few seconds running either. Perhaps you or someone else has?

[russc]

yeah, you know what...disregard that. That situation would start up fine, but then die after 5 seconds.