Daughters 2012 Tiguan, 2.0, SEL Premium with AWD, bought used at 70,000. No issues until last four months. It had a P0299 start about 30 days after purchase but never seemed to be an issue. OBDII code reader said underboost but live diagnostics with Torque and right foot italian tune up or test always showed positive boost levels and it ran like it should.
Two weeks before leaving for college it threw a P0301, did some shuddering at start up a few times, and went away. No CEL flash. By now we are at 85,000 miles, OIC interval is good, full syn, not burning hardly anything. Used to us with good history records.
Replaced all four spark plugs with a new set of NGks pregapped rom DAP and a new Bosch coil for Cyl 1. Did well for four weeks. No misfire, no shake, no CEL. If it did show a CEL, you could clear and it would run fine for 3-5 days. No flashing CEL or any CEL most days. You could get on interstate and romp at 90+.
Three weeks later it flashes CEL at ignition, and ignition only, briefly, disappears and then sometimes retains a CEL or doesn't but still has shake at startup and doesnt like going beyond 4K . It also threw P0300 and P0301 for two days but I've now put three additional Bosch Coils in and moved the new replacement installed four weeks ago from Cylinder 1 to 4 and put a new coil in on Cylinder 1. P0300 is gone. No change in code readings other than P0300 has disappeared and never returned. After the three new coils and swap it ran just fine for 4 days. No code, no shimmy or shake. Then....it went sideways again.
It still flashes a CEL light at start-up for like 2 seconds and never stays, idles up kinda rough, then comes down and smooths, doesnt always throw a code, doesnt like to roll beyond 4k but does some rough idle and engine pull. The flashing CEL never remains. Its short and gone.
I've checked harness wiring to coils and they seem fine. Nothing loose. Fuel MPG is roughly usual but can't clarify since she does not drive it every day. Oil level still good. It does not want to rev above 4K on highway though according to her. I may have to check. No other cylinder misfire code was ever present.
Any help is thanked in advance.