Rough Idle First 30 Seconds Cold Engine
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AudiWorld Junior Member
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Rough Idle First 30 Seconds Cold Engine
Every time when starting a cold engine (not driven for six hours or so) for the past couple of weeks, I have a rough idle for about 30 seconds, like the engine is missing. Then, by itself, the rough idle goes away, and no issues until next cold start.
After a couple of weeks of this behavior, one morning the check engine light went on with the rough idle. Had mechanic check the codes, which suggested #2 cylinder missing. #2 plug looks fine, plug wire looks fine, and no visual problem with the coils or connections. Cleaned connections and cleared codes. Next morning, rough idle and check light comes on again. Still, everything seems fine after the 30 seconds of rough idle.
Anyone else experience this, or have good ideas for diagnosing? It is tough to "catch it in the act" since it happens just once with a cold start and then has to get "cold" again to repeat.
'99.5 A6 2.8, 102K miles, full 90K maintenance done at 90K miles.
After a couple of weeks of this behavior, one morning the check engine light went on with the rough idle. Had mechanic check the codes, which suggested #2 cylinder missing. #2 plug looks fine, plug wire looks fine, and no visual problem with the coils or connections. Cleaned connections and cleared codes. Next morning, rough idle and check light comes on again. Still, everything seems fine after the 30 seconds of rough idle.
Anyone else experience this, or have good ideas for diagnosing? It is tough to "catch it in the act" since it happens just once with a cold start and then has to get "cold" again to repeat.
'99.5 A6 2.8, 102K miles, full 90K maintenance done at 90K miles.
AudiWorld Senior Member
Joined: Dec 2003
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Missing engine - there's your problem!
Just kidding. I think you mean "misfiring".
I think you need one or more new injectors. I'm no expert, but I think if the ignition stuff (plugs, wires) are ok, misfires are caused by dirty or bad injectors.
I think you need one or more new injectors. I'm no expert, but I think if the ignition stuff (plugs, wires) are ok, misfires are caused by dirty or bad injectors.
AudiWorld Super User
Joined: Aug 2002
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From: Warwickshire
It sounds like it could be the coil but you would .....
most likely get missing on No.2's paired cylinder as well.
I would try moving two of the coils around and see if the fault moves. ASAIK all three coild are identical so they can be swapped freely.
If the fault stays with No.2 then it is lead, plug or injector, I would go with plug first.
The rich mixture at cold startup puts a far higher load on the plug, coil and leads so missing when cold often clears as the mixture gets more lean as it starts to warm up.
I would try moving two of the coils around and see if the fault moves. ASAIK all three coild are identical so they can be swapped freely.
If the fault stays with No.2 then it is lead, plug or injector, I would go with plug first.
The rich mixture at cold startup puts a far higher load on the plug, coil and leads so missing when cold often clears as the mixture gets more lean as it starts to warm up.
AudiWorld Senior Member
Joined: May 2003
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You have a bad MAF.
My 4.2 was doing the same thing. The cold start function is making the engine run too lean and you are getting misfire due to unstable combustion. Replace the MAF, pull power off the ECU for a couple minutes, and it will be fixed.
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AudiWorld Super User
Joined: Aug 2002
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From: Warwickshire
In 20 years of having fuel injected cars the only injector problem...
I have ever seen were with K jetronic.
All of the electronic injectors have never given me a problem so I would say it is a good suggestion but possibly after further diagnosis on the ignition side is carried out.
All of the electronic injectors have never given me a problem so I would say it is a good suggestion but possibly after further diagnosis on the ignition side is carried out.
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