'97 B4 215,000 miles of which I've added the last 115,000. First thing I did when I got my VAG-COM was re-calibrate the egr values to minimize intake clogging. That was probably 100,000 miles ago.
I've suffered persistent 'limp mode' issues since I've owned the car. One big hill on my daily commute and could never use 100% power or I'd wind up in limp mode half way up. Learned to drive around the problem or reset ignition switch/ecu on-the-fly on the subsequent down grade.
Few months ago began getting 'mil' and 00560 codes and occasionally a 00575. Vacuum hoses were shabby, had never done any intake/egr service of any kind, knew nothing about these systems or their function. Kept resetting the code(s) to extinguish ''mil'. But the 'mil' was coming on more and more frequently and VAG-COM always showed 00560.
Guided by the many invaluable posts here I began:
Started diagnosis/repair with the cheapest item-hoses. New silicone rubber throughout-no change in 'mil' behavior.
Checked egr diaphragm-it held vacuum
Checked vacuum from control solenoid (N75 right?)-20 in. at idle and varying with engine load/speed.
Removed intake air hose at egr and
holy darkness!! Intake completely clogged with carbon and soot, couldn't see past the egr actuating rod. Yikes! Removed intake (moderate pita) and the entire manifold was completely clogged up with the accumulated carbon/soot. I picked, scraped, gouged and brushed an entire CoolWhip container full (overflowing actually) of carbon out of the manifold. Then I blocked the 4 intake port openings, added 2 dozen (I counted them 3 times before adding them) 3/8 machine nuts, poured in about a cup of mineral spirits and blocked the intake opening. I let this sit in many different orientations and shook it vigorously from time to time while I cleaned up the intake ports on the head. There I just used a scraper to ease the edge of the accumulated junk to give a smoother transition from the clean manifold runner to the still dirty intake passage. I turned the engine to each cylinder's compression stroke before scraping and then vacuumed/blew each intake port/passage out before moving on to the next cylinder. An hour or so of soaking and shaking with the hardware had cleaned the manifold well (counted the nuts again as they came out) so after blowing it out and air drying it I reassembled everything. Wow, most of a Saturday gone, I'm filthy dirty head to toe but I figure I've seen the last of the danged 'mil' for awhile. And the engine, as you might expect, ran soooo much better. Smoother at small power settings and much, much more power at 100%.
the next day running errands in my new, super powerful TDI when the 'mil' lights. This being a family forum my exact response in unprintable but you can use your imagination....
Further reading of these truly invaluable posts and the subject of the egr cooler surfaces. Hmmm, didn't look at it very carefully as I moved it aside while taking the intake off. Sooo, removed intake air tube at egr again and ran engine while sucking the egr valve open. Nada, zip, zero. No noise, no visible exhaust nothing coming up through the egr port. Removed flex pipe at egr cooler discharge end, start engine-only the slightest hint of exhaust through the cooler. Oh boy, what now? Dismount cooler again leaving coolant lines attached, lift cooler where I can see into the inlet end and it looks just like the intake did-fully clogged with carbon/soot. I had to use a long length twist drill and drill motor to unclog the cooler's individual tubes. I used great caution not to damage the tube(s) while clearing them and couldn't get to all of them with the drill so the cooler is not completely unplugged. I'd guess it has about 60% of its capacity restored. Reassemble (again!) and now the engine seems to run even better. The idle is smoother and the part power throttle response is better. Drove the car about 10 miles with no 'mil'. Connected VAG-COM, no codes registered. Logged about 3 minutes of MAF data showing egr duty cycle between 19.9% and 64.1%.
No more 'mil' and
no more limp mode. Can use 100% power in all gears and have no problem.
Conclusion-intake cleaning/service is probably required in any high mileage 1z and might be recommended as a 100,000 mile routine service item. Your mileage may vary but my results have been dramatic and well worth the effort. On a 1-10 scale this whole project, had I done it all at once, would have been about a 6 pita.