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Intermittant misfire Audi A3 1.8T (1999)

I have this intermittant misfire on my Audi A3 1.8T (1999) . Engine momentarily loses power - can occur when cold, hot, under load or idling. Taken it to 3 garages, one an independent Audi/VW specialist and nobody can identify the problem. No codes appear on the diagnostic log and there are no warning lights. New spak plugs and Air mass flow meter have made no difference. Any ideas?

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Sounds like carbon build-up in the cylinders. Take it and have it put on a machine called a "Motor-Vac"

Posted on Jan 28, 2009

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Intermittant misfire audi a3 3.2


Alright listen...I believe these undiagnosed issues are because of bad fuel. It could be ethanol or just dirt. My car had performance issues and eventually would stall. It occurred mostly when I was low on fuel and the dirt would then be pulled up into the engine. If you have misfires or the diagnostic suggests injectors or manifold start with removing and cleaning the tank and fuel lines. Then recheck and go from there.

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If it is not still misfiring, clear the code. it was intermittant and nothing to worry about.

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Hi, I have a 1995 1.6 monomotronic VW POLO (eng code AEA) and the engine cuts off momentarily and resumes normal operation after a sec or two. At the same time the engine rev gauge goes down to zero(not...


Sounds like your on the right track. I would check for loose wire connections around the fuse boxes. Pull any fuse that has to do with the ignition or ECM/PCM, as these do corrode and loose connection. I would not rule out the ignition switch either, as the problem you are having is intermittant and switches are bad for intermittant problems. They heat up and loose contact, and regain contact when they cool down, and usually in a couple of seconds.

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I am having ongoing problems with the truck miss firing and rough running. Timing is ok, replaced cap and rotor,coil. It still starts rough,idles rough and misses when at cruising speed,although it seems...


Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).

When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.

Hope this help.

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take to autozone and have them check the engine light code to start it's free

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determine when it misfires, and isolate cylinders. a poormans method is use an infrared temperature gun (one with high range, 700 degrees or more is preferable) and with engine held at rev(say 2500) point at each exhaust port 1 by 1, misfiring holes have colder exhaust than firing holes.
If the misfire is momentary or intermittant, or caused by defective cam or crank sensors, you should see professional help...those problems require more advanced equipment to get the 1st time, unless you dont mind lobbing expensive parts randomly till you get lucky

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check fuel filter and check fuel for water or contaminents
then check fuel pressure with gauge also while driving
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recheck spark plugs - did you crack any on installation/removal/installation?
what are the codes and description if stored?
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