What could cause an engine to run this rich?

[orochidp]

Howdy folks,
My car has been getting pretty crap mileage. I bought it used in horrible, horrible condition and have restored it to mostly working order. I've fixed every rattle, bang, vibration, and leak that the poor engine had. It's not throwing good money after bad if you're enjoying the experience, right?

However, my engine runs insanely poorly in stop and go traffic.
In the city, I get ~15MPG. On the highway, I recently got a hair north of 30MPG.

I've replaced the standard plugs/wires/cap/rotor, the timing belt (yes, I've triple-checked the timing), the O2 sensor, and a few other odds and ends. Compression is good and even across all 4 cylinders. The engine has picked up a bit in terms of response and acceleration, but the mileage hasn't budged a bit.

My hunch is that it's running very, very rich since the MPG goes back to normal once I maintain a decent speed. When I first start and when I turn off the engine, there's a smell of gasoline outside the car. There's no smoke and the engine's not missing. There are no CELs, and there are no puddles under my car.

This is my first car, so my knowledge of what else to investigate is pretty lacking.
My theories are as follows:

1. Bad coolant sensors keep the engine running rich. However, my engine temp gauge works perfectly fine - I found out how well it worked when my water pump died. I don't know if the same sensor for the gauge is used to report that data to the ECU, though.

2. Possible exhaust leak at the exhaust header. I've got no reason to suspect this other than the fact that this could give the (brand new) O2 sensor bad data, thinking it's running lean.

3. Possible vac leak. I've sprayed carb cleaner from the intake hose to the back of the intake manifold without any noticeable RPM change. I've changed and cleaned the whole PCV system since there was a bit of oil in my intake. What other locations should I look to confirm/rule out a vacuum leak?

I'd appreciate some advice on other possible culprits or tricks or something. I'd take it to a shop, but the bill for analysis would be more than I paid for the car. Plus, what's the fun in that? I've done plenty of searches of this forum and found some similar issues, but none quite the same. I've attempted the repairs for their problems without success, though.
I also assume I'll need a new cat if the engine is truly running rich.

TL;DR: I think it's running rich and I've done the basics, what advanced wizardry should I try/what simple thing have I overlooked?

[Josh]

-have you checked your timing? This "could" be it if its been adjusted wrong and over compensated with the idle screw.
-Is your car a SOHC or DOHC?
-far fetched but whats the millage of the car? could just be tired
-are you using excess oil?
-maybe bad injectors, have you run fuel injection cleaner through your system recently. could be a dirty system.
-If its a 94-94 then it could be the EGR you can suck on the vac line and see if its moving properly.
-could be a week spark from the coil. if its a 94-94 then that could be the case as its internal coil on the distributor and they are known for having issues.

A couple of things to look at if you haven't done so already.

[orochidp]

Oh, my bad. It's a 1993 SOHC. It's got a solid 126k miles.

I follow the rules when it comes to oil, and I ran a can of Seafoam and a bottle of Techron through my gas tank a bit ago and nothing has changed.

As for timing... I've fixed the valve timing, but I haven't been able to do the ignition timing due to the bottom of the timing cover being busted up. The little sticky-outy bit with the timing marks looks like it got attacked by a broken belt, I can't read it. It's a strong possibility that the timing's too retarded. It would explain the gas smell. To be honest, I thought that the ECU took care of the timing once it left the closed loop mode, but that sounds a bit dumb now that I type it out.

The EGR is another possibility that I can look into. Is that on the back of the intake? I don't think I have ever contorted my body far enough to see where it is.

As for the distributor, what can I do to test that for this particular problem?