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'03 996 C2 A little background of the path to where I am now. New to me vehicle of about three weeks. Took in for emissions and failed the readiness test. I'd only put a 150 miles on the car and had the battery disconnected the weekend before to charge it. Made sense, so I drove it to work to put some additional miles. Drove another 30 miles and got a CEL (P0507, P0171, P0174). Did some reading and cleaned the MAF as instructed. Drove it for another 45 miles and same codes.

Did a little more reading. Took off the air intake (Fabspeed) and check for any cracks or tears (nothing). Cleaned the throttle body (not much there, but cleaned what was there). Re-assembled everything. Next morning drive it to work and start getting a surge at idle (1200-1800 rpm). It even feels a bit like it surges when I am on steady throttle at speed (maybe psychosomatic).

A couple other things, when I cleaned the throttle body I removed the the two screws that hold the plate and pulled the plate out to make sure everything was cleaned well. I'm fairly certain it went back in correctly, as there are two tabs and two screws that make it nearly impossible to reinstall it incorrectly.

I did note that the oil filler tube had been cut and joined together with a piece of rubber tubing. It had pulled apart when I pulled off the air intake. Of course I re-attached it as it was found. I mention this because in another posted about surging idle there was concern that all the vacuum hoses were properly attached and that even the oil filler cap was on tightly.

Any ideas. I've taken it to a local indy who is stumped as well.

Edited by LostSouth
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I would first replace the oil filler tube, impossible to get such a thing air leak free after it was broken, then perform a test with a smoke machine for further air leaks.

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I had a surge on my car, e-gas, a couple of years ago. It would happen at idle and while cruising at a constant throttle position. It would also through on the ABS lights, but I never read the code as it would go way if I turned the car off. Cleaned everything a few times and checked for leaks but the problem would not go away. Finally one day I lost the throttle pretty much altogether. Limped home with little more than idle. I borrowed the throttle body from a friend's car and put it on my car and the problem was gone. Bought a new throttle body and the problem has never returned. So the e-gas throttle bodies can go bad.

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