It wasn't long after I got the misfire to stop that it came back again. As before, at a cold start the car runs fine for about 3 seconds then you can hear a slight misfire for about 5-10 seconds and then it runs fine. Sometimes the check engine light flashes, sometimes it doesn't. So here's where I am right now. In the last year and a half the spark plugs, spark plug wires, coolant temperature sensor, and driver's side cam position sensor have been replaced. In the last few months I've replaced the ignition coil pack, fuel filter, fuel pressure regulator, intake air temperature sensor and cleaned the MAF and throttle body and done a throttle body alignment. I replaced the rivets in the SAI pump and the SAI system is working now. Not really sure where to go from here. The Haynes manual says the car doesn't use the oxygen sensors until they reach 600 degrees. So that rules them out and that makes me think it must be a sensor. The only sensors I can think of that haven't been replaced are the crank sensor, the passenger's side cam sensor, the oil temp sensor (the gauge works), and the MAF. Is it possible the coolant temp sensor has gone bad already? The gauge still works. Is there anything I could get a reading on in vagcom that would give me an idea of what is wrong?

 

Just ran the car from a cold start while watching vagcom. I went through the list of measured values and watched the misfire recognition, coolant temp, intake temp, and MAF. I ended up with 172 misfires so it's worse than before. Coolant temp read 4 degrees celsius and climbed what seemed normally to 75 degrees in about 10 minutes. Intake temp read 6 degrees celsius and did not go up much from that. The MAF is a bit odd though. Vagcom says it should read 2.8-5.6 at idle. Without the car running it read 27 g/s. Not sure if that's normal. Started the car cold and it read 11 g/s. By the time the car stopped misfiring it was down to 7.5-8 g/s. By the time the coolant temp was 75, the MAF had slowly worked its way down and seemed to settle at 3.8 g/s. I turned the car off and the MAF read 27 again. Started it up now that the car was warm and it read 4.2 within a second. Found this PDF on diagnosing a bad MAF. I had already cleared codes so I couldn't check fuel trim. I did the load test on it. Running up to red line in 2nd gear the MAF had a max of 138 g/s. 80% of the stock hp should be 152. I only got 72%. Does it look like my MAF is bad?

 

Your MAF stuff sounds normal to me, but it can't hurt to try cleaning the sensor and see if that will raise your WOT MAF readings.

Have you checked for vacuum leaks? How is the condition of your vacuum lines?

 

Thanks for the reply. I forgot to mention I replaced the vacuum lines last summer.

 

So if the MAF seems fine, I'm thinking something might be getting into the cylinder. Either a small coolant leak that is letting coolant in the cylinder when the engine is up to temp after the engine is shut off or a leaky injector. I don't have any coolant in the oil or any oil in the coolant. So I'm betting leaky injector. I pulled the fuel pump fuse and relieved the fuel pressure then let the car sit for a while. When I put the fuse back in and started the car, the misfire was substantially less. I let the car get up to temp and relieved fuel pressure again. I'm waiting for the car to cool down and try it again. If I get the same result, does it sound like a leaky injector? I'm thinking I still got a small misfire because I gave the fuel pump a few seconds to build up pressure before trying to start the car and it was long enough for the injector to leak some fuel into the cylinder. Whether it's a coolant leak or a leaky injector, it seems to be on cylinder 2 according to the codes.

 

Put the fuel pump fuse back in and only waited a second with the ignition on before starting the engine. It ran for a few seconds without a problem. Then had a very slight misfire for 5 seconds. Then it ran fine. Sound like a bad injector? I know I could just switch the injector to a different cylinder and see if the misfire moves but I don't plan on removing any injectors without new o-rings.

 

The car has sat a couple of days. I thought I would check to see if there's any fuel pressure at the rail. I don't have a gauge so I pulled the fuel return line at the rail and then used a hand vacuum pump to put a vacuum on the fuel pressure regulator to see if anything came out. I got nothing at all. Not even a drip. I turned the ignition on for a few seconds and then tried again and got nothing. I hooked everything back up and ran the car for a few seconds. Shut the car off and as quickly as possible tried again. Before putting vacuum on the fuel pressure regulator I pulled the fuel return line and a small amount of fuel ran out. I put vacuum on it and got nothing. The Haynes manual says there should be 12-15 in. Hg vacuum on the fuel pressure regulator at idle. I went as high as 20 in. Hg and was still not getting anything out of the return line. Does this sound right or am I losing fuel pressure somewhere? The Haynes manual says that the fuel pressure shouldn't drop below 35 psi in 10 minutes or you have problems. I ordered o-rings and filters for the injectors so in a few days I will be pulling them and moving the #2 injector to see if the code moves cylinders.

 

Bought a used injector. Put the used injector on cylinder 5 and moved the cylinder 5 injector to cylinder 2. Cleared codes this morning. I just checked codes and it still says random misfire and cylinder 2 misfire. Both intermittent.

 

Pulled the spark plugs. All of them looked normal except for cylinder 2. It had a glazed appearance to it. From looking around online, this is the description of a glazed spark plug: "Glazing appears аѕ а yellowish, varnish-like color. Thіs condition indicates thаt spark plug temperatures hаve risen suddenly during а hard, fast acceleration period. Aѕ а result, normal combustion deposits do nоt hаve аn opportunity tо 'fluff-off' аѕ they normally do. Instead, they melt tо form а conductive coating аnd misfire wіll occur." I also found another that said to check timing. I put new spark plugs in it and it seems to be a little better. But every time I've tried changing something it seems like I've fixed it and then it just goes right back to where it was. I don't understand why the cylinder temperature would suddenly rise. Especially since it was the only spark plug that looked that way. The car doesn't overheat. If anything I think it takes longer than it should to heat up. Is there anything else that could be causing this? Oil or coolant leaking into the cylinder? The neighbor, a diesel mechanic, was behind me on the highway the other day and he said there was smoke coming out of the exhaust but it wasn't blue. I do have a small exhaust leak at the flex pieces before the cat. I did an oil change about 1500 miles ago and a coolant change about 700 miles ago when I did o-rings. There wasn't any oil in the coolant nor coolant in the oil.

 

Cleaned the injectors and replaced their filters and o-rings. They all seemed to have the same amount of flow and spray pattern. I still got 15 misfires on cylinder 2 on a cold start. I logged coolant temperature with vag-com while I drove around for 20 minutes. It never went over 183 degrees and it was 60 degrees outside. When I got back from the drive I shut the car off and let it sit for a few minutes. I started it back up and vag-com showed 5 misfires on cylinder 2. I probably wouldn't have noticed them if I hadn't had vag-com running. I'm starting to think it has to do with the head gasket. I just flushed the heater core so it will take me about a week to see if my coolant level is dropping. The car has never overheated on me but the previous owner may have had it overheat and never mentioned it...purposely. It did have a leaking coolant hose when I bought it. So I guess I'm going to have to do some tests to see if the head gasket is bad. In the meantime, here are some pictures of the spark plugs I just replaced. The one on the left is from cylinder 2. I don't know what cylinders the other two are but they all looked similar except for cylinder 2.