Re: Intermittent misfire theringmeister at
Mon Oct 16 03:59:33 PDT 2017

We just went through a pretty frustrating scenario with my sons B5 S4. Sort of the same symptoms. Long hard start and then rough running once it did start. We did not get any CEL. Chasing the problem, he replaced the fuel pump and pressure regulator both but that did not solve anything. We finally got a set of used injectors, had them sent off to Marren for service and installed them. That solved the long-crank starting but not the rough (barely) running until warm. That was finally solved by replacing the coolant temperature sensor in the back of the head. We never saw a code for that but as soon as it was replaced the problem went away. Just a thought if nothing else works.

Wylie Bean
Central NC
90 Coupe
91 90q20v
91 200q20v
92 UrS4
01.5 S4
08 Q7

----- Reply message -----
From: "Cody Forbes" <cody at>
To: "Tihol Tiholov" <t.tiholov at>
Cc: "quattro at" <quattro at>
Subject: Intermittent misfire
Date: Mon, Oct 16, 2017 12:33 AM

Could be a leaky injector(s) putting a bunch of fuel in the engine overnight. Could be the opposite of they: fuel pressure leaking down overnight and not priming quite enough before starting. Could be oil leaking out of the cam phasers over night maybe.

I'd try some injector cleaner stuff. It's not a miracle product, but it can't hurt.

-Cody Forbes (mobile)

> On Oct 15, 2017, at 8:05 PM, Tihol Tiholov <t.tiholov at> wrote:
> Hi, all.
> The patient is 2002 A4q 3.0, auto.
> Occasionally, when I start it first thing in the morning it'll misfire with
> CEL coming on or even blinking. Usually, when damp and cool, close to
> freezing. After 15-20 seconds with a bit of throttle input (to which the
> engine doesn't always react), it clears up and it's fine for the rest of
> the day. After shutting down and restarting, it's all good.
> Idle is often a bit rough, but again intermittently. Not sure, if there is
> a connection.
> Pulled trouble codes and they were all intermittent:
> - Random cyl. misfiring,
> - Every cyl. misfiring individually, except #6, 5 codes total for this,
> - Catalytic converters heating circuits.
> Seems like something resets itself at 2nd restart.
> This morning it was misfiring at first start with CEL blinking, then after
> shutting it off and restarting, no CEL, all was well for several restarts
> and 30-40 kms short trips.
> Any info, BTDT's, etc. welcome
> -- 
> Tihol
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