My girlfriend has 2002 lancer with a 2.0 engine. she took a trip home this weekend and she said on the way up there the engine was bogging pretty bad. when she got back. it stopped, but every nowand then i will feel it stumble at idle. we took it to autozone to get a diagnostic test because the engine light was on. this is what the read out said.

catalyitic converter defective (i doubt it)

engine misfire or running lean condition

large vacuum leak

engine oil leakage into exhaust valve-valve guide seals

piston rings.

im a classic car restorer so i only work with non-computerized classic v8 engines, but im a mechanic so its the same principals. the plugs are also new. before i tear into this thing, has anyone experianced these symtoms? what do yall think?

 

Plugs gapped correctly?

Spark plug wires in good condition? Replaced recently?

 

I bet it is the catalyctic converter. if the car is about 60,000 to 100,000 miles it should be the cat converter.

My friend has the same issue. went to 2 auto tech they all said it is the cat converter

or wrong spark plug gap orvoltage regulator

 

Not all that crap its not the cat.

 

What was the code? I doubt its all that, prabably an ignition missfire. Does it have a coil on plug set up?

 

the plug gap is correct. as far as the code, i was given an autozone print out and i dont see a code on it. it does have the coil per plug set up.

 

Too fast an idle speed. The powertrain control module (PCM) will maintain normal idle speed and compensate for a small vacuum leak by closing down the throttle body air bypass. But if the leak is too large and the idle control system cannot compensate for the extra air, the engine may idle too fast. Common leak paths include the throttle body gaskets, intake manifold gasket, any of the engine vacuum fittings, hoses or vacuum-operated accessories (such as the power brake booster or EVAP canister purge valve). It is even possible that leaky O-rings around the fuel injectors may be allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft.
A rough idle or stalling. A large vacuum leak can lean the air/fuel mixture out to such an extent that an engine will not idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can a loose positive crankcase ventillation (PCV) hose, a leaky PCV valve or the wrong PCV valve (one that flows too much air for the application). If somebody replaced the PCV valve recently, they may have installed the wrong PCV valve. The rough idle in all of these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, which may be enough to cause a vehicle to fail an emissions test.
Hesitation or misfiring when accelerating. This may be due to a vacuum leak, but it can also be caused by dirty fuel injectors, a weak fuel pump (low fuel pressure) or a faulty fuel pressure regulator. It can also be caused my ignition misfire due to worn or fouled spark plugs, bad spark plug wires, or weak ignition coil.
The important thing to keep in mind about vacuum leaks is that they have the most noticeable effect at idle. At part and full throttle, more air is entering the engine through the throttle opening so a vacuum leak has less effect on the air/fuel ratio.

 

Well try to get the diagnostic code (dtc) and it'll make it a LOT easier to help. Most likey you have a bad coil, you just have to identify what cylinder is missing.

 

You could always drop the exhaust and drive it to see if its any better, this will tell you if the cat is clogged.