p0420 after new cat, o2, and maf

[CaseyVR6]

I've got a 00 Jetta VR6 5sp.
200k miles.

I recently (past few weeks) put in a new cat, o2 sensors, mass air. After which I cleared the codes.

Symptoms: Yesterday, first start of the day. The car took 3 tries to get it to fire up, and when it finally started it was groaning and shaking and acting like an old lawn mower. I let it run for a minute or two thinking it would clear up. If I put the pedal to the floor the car would slowly groan up to a max of about 3200 rpm's. Trying to drive it was an embarassing nightmare, where pulling away from a red light was gruelingly slow. After the car ran for about 15 minutes it finally found it's feet again and ran like a champion. It's happened like that before, just not so extreme and not since I replaced the parts. Through all the spitting and growling, no CEL.

Today, on the way into work while the car was running fine I get a P0420 code showing up. As it stands today, the only things I'm aware that the car needs are shocks and a front wheel berring (all on their way). Any ideas?

Perhaps unrelated, but the idle is a bit inconsistant, there is some shake in the engine, and the lights flicker (closer to fade in and out quickly without going out) but that's about all I've got to physically show anything.
* sorry for the long thread

[ctuagent117]

maybe engine mounts? were the parts you installed oem? i had a problem with stalling, and rough idle. oddly they whent away when i chipped it. well hell you put 200k on that thing that is the most ive seen an mk4 go with out any major problems, youve had a good run

[veedubmechanic]

cat bank 1 eff below threshold.

you replaced the cat recently with a vw one or aftermarket?

the symptoms you gave seem like a bad throttle body exactly ( or one not adapted properly)

replace the coil pack recently? spark plug wires? those can cause this code if there arcing.

[CaseyVR6]

The replacement was a VW Cat, california was a bit demanding with that.

The plug wires are new, however the coil is about 2 years old. I can test the coil easy enough, how would I test the throttle body? Can't just spray that with water and see what it does. It is running fine again today, which confuses me except to think that the rain was screwing up the coil. All I see are dollars floating away when I open the hood to work on it. lol

[veedubmechanic]

Originally Posted by CaseyVR6

All I see are dollars floating away when I open the hood to work on it. lol

hahahahahahaha

you can mist water on the coil and if it arcs its time to replace it.
also the throttle body, you have lots of miles and its problably time to replace it anyway.