X-Ravin

Ok so here's the deal. I've always had a rough idle, not like a lopey cam idle. I also get the EGR code only on long highway trips. But I didn't have this issue until very recently. I started tuning on a stock $6E and the car ran great until it though the idle was too lean and started making it pig rich, then the idle got really bad again. So I was slowly working on this when suddenly the car started idling really bad.

So I plugged in the scanner and found that when the car starts up in open loop, the O2 starts at around a few hundred mv, then after about 30 seconds drops to 4mv and pegs there. It will only change when the BLM's get ridiculous, like 140+. It can't be running lean, the exhaust is gassy and the car idles worse and worse as the BLM's go up and up. Even when they are that high, the O2 sticks to 4mv most of the time.

When cruising things get better, some BLMs are rich, some lean, but usually only +-4 from 128. At 45mph I've always had a noticeable misfire. However a new thing that has started since this problem began is knock. Any aggressive (> 40%) throttle will start knock counts. Oh and I always use 93 octane gas.

SO, I replaced the O2 sensor (which is heated and the old one was only 2 months old), and there was no difference at all so something is dumping air down the exhaust manifold. My idea is that the EGR valve is badly stuck open, or maybe the AIR system isn't working right. I'm not overly familiar with those systems other than their basic operation. Can some of you experts lend me some brain cells? The weather is getting nice and I'd like to make it to ThirdGen Fest

EDIT Mod list:
350 TPI (87 top end)
Mild .480/.488 lift cam
1.6 RR's
Edlebrock headers (look like mid-length maybe)
No cats, flowmaster
3.73 gears

X-Ravin

So I found that the vacuum routing was all wrong, so I redid all of it, but the car runs no differently. This seems odd because the FPR wasn't getting vacuum at all, I would think the car would idle differently with vacuum applied to the FPR. Basically when the car first comes up in open loop, the O2 voltage starts around 450mv and then starts to drop at a constant rate down to 4mv where it pegs until closed loop kicks in and BLM gets above 136 (it will max out after a few minutes).

I applied vacuum to the EGR when the engine was off and it held, it won't hold vacuum when the engine is on, but I think that's normal. However, the engine runs no differently if the valve has vacuum or not! In fact the valve had constant vacuum before I rerouted the vacuum lines, but again no difference. Bad valve? Any other ideas?

X-Ravin

Ok, I played with the EGR some more, this time it won't hold vacuum either on or off. I boosted up the MAF tables for idle about 1.25. This makes the O2 happy in both closed and open loop. My BLMs are mostly trying to lean out across the throttleband. My knock is gone. Did a quick WOT jab and only picked up a couple of counts when jammed the throttle, so something is more righter. Idle smells very rich and is still rough. Ordered an EGR valve and will be putting it on this weekend. I'll also check the injectors and the FPR while I'm at it.