I accidentally posted this in the MK4 forum yesterday; realized that it should probably be here in the VAG-COM Diagn. Forum. My main questions are those that are in bold.
I have a 2004 Golf, 2.0 that I purchased from someone who was having misfire problems with it which he could never figure out. According to him, (and I have no reason to doubt him at this point...since many of the replaced parts were in the trunk), he replaced the fuel pump, fuel filter and relay, fuel injectors, coil pack, plug wires and plugs, rear O2 sensor, water pump and thermostat along with having the timing redone. Nothing seems to have resolved the problems.
The problem which the car still has is that it randomly misfires. On some trips, nothing happens at all, on others it might end up misfiring for anywhere from 20 seconds to several minutes. It only throws the following error codes: P0300, P0303 and P0304. Funny that the misfires only happen on cylinders 3 and 4, although almost always just on 4.
It has the BEV engine. The coilpack (1 pc, not the 4 separate ones on this model) does not have any cracks. Neither does it or the plug/wires arc when I spray them down with a little spray bottle while running. Had he not said that he had already replaced the coilpack, I would have already done so anyway, just to be sure.
In the meantime, I was able to procure a laptop with the VAGCOM on it from an acquaintance. What I have done so far is the following:
1. Replaced plugs with the proper plugs called for (since I have read in several places on the site that the VW's are touchy with their plugs.....also noticed that the plugs that were in there were of a different size (less reach). The ones I put in are NGK PZFR5D-11. Autolite 3923 is what was in there.
2. I have done various tests with the VAGCOM....making quite a few logs, hoping to catch it when it misfires. Unfortunately, I can only log in my garage (laptop battery is dead and won't hold a charge). So they are all at idle. I'll get to those results later.
3. I cleaned the MAF with contact cleaner
4. Checked Air filter (clean....K&N filter)
5. Checked as best as I could for vacuum leaks, found none
6. Performed Throttle Body Adjustment
7. Cleaned Throttle Body as best as I could without removing it from intake.
8. Checked virtually every connector I could, cleaned them with contact spray
I think that's it; although I might have forgotten to list a thing or two.
While playing around with the VAGCOM program, I noticed the following:
Group 000, 5th box (Throttle Valve Potentiometer), used to always read around 6 when idling with a warmed up engine. After I cleaned the inside of the Throttle Body, it now usually reads 2-3. I don't know what value it is supposed to read – maybe someone here knows. Should it read “0” with no throttle applied, then maybe I need to take the throttle body off completely and do a more thorough cleaning job.
During the few times I've caught the misfiring happening while hooked up to VAGCOM in the garage, in Group 001, 3rd box (O2 Sensor %), it automatically goes to “0.0” and stays there. Normally, it fluctuates around the -3.6 to +3.6 %. But it just goes into what I guess is referred to “open loop” and the “Inject period” of Group 002 stays a fixed value, i.e. no longer fluctuates.
Does this mean my pre-cat O-2 sensor might be going out? Or is it something else telling the computer to now ignore the values from the O2 sensor?
Also, the 1x111111 value, shows the “0” in the 4th from last position, meaning Lambda control not OK. I doubt it's a problem with compression.....when it runs without misfires, it purrs like a new engine.
Here is a copy of a portion of one of the logs: (Group 000, 001 and 033). This one is where it's misfiring.
Now here is a copy of the same modules, where it's running great (same groups)
Is there a test with 3 specific groups that I should run that will give you folks better info?
Also, is 760 rpms the proper rpm's for idle? I believe I saw somewhere in a Bentley manual that it was supposed to be 680......my Haynes manual doesn't state anything.
Any help that you folks could give me would be highly appreciated.