It only got this way after warming up, so when I initially test drove it I didn't really catch it.
It ran like a top on the highway, and when I came to stop I thought the car had died because it was idling so smoothly. Then, about 10 seconds into sitting at a light, the rpms dropped just a hair and the car would get all burbly again. It got so bad sometimes that I probably couldn't have held a cup of coffee without spilling it.
My HVAC system is on the fritz, but when the AC does kick on it totally kills the lumpy idle and becomes smooth as glass. The car ran though an emissions test with flying colors. Oddly enough, during the 5 minutes of the test after I shut the AC off, the car idled fine. Normally the burbly idle comes back as soon as I turn off AC. My CEL never came on.
*I changed the spark plugs- the old ones looked fine if but a little worn- No change
*I checked for spark by pulling the wires at the plugs with the engine running- they shot huge sparks out of each end.
*I used enough propane to BBQ a buffalo in searching for vacuum leaks- none found
*Did the grounding mod- no change in idle, but the car runs better in some way I can't pinpoint.
*Changed the coolant temp sensor with cpu reset- immediate change, but the idle still got intermittently lumpy at stoplights. Watching the tailpipe, the exhaust would burble noticeably every 5-15 seconds at random (as opposed to burbling constantly)
*PVC valve replaced- no change
*Air filter and MAF cleaning- no change.
*I replaced the fuel filter and filled the new one with seafoam before installing it. The gas coming out of the old filter inlet looked like dirty coolant. There was an immediate change in the idle, but it still burbled at random every 15 seconds or so but less "hard" than before.
*I read that leaky intake manifold gaskets may be a culprit. Even though I searched with propane I couldn't find a leak, but If I manually revved the engine I could hear a hiss open up somewhere around the front pass side of the valve cover. So I took out an intake manifold bolt out one at a time, lubed it with anti-sieze, and reinstalled at 1/2 torque, then went around and did a final torque to spec.
That pretty much gave me a 90% improvement overall in the idle smoothness. It's still doesn't hold that "smooth as glass" sensation after 10 seconds at a light, but it doesn't feel like the engine is trying to shake itself apart.
Curiously, the front pass side manifold bolt was oil drenched at the threads. All the other bolts were dry.
While I was poking around the engine (waiting for paint to dry), I found that the engine leaked 2 or 3 oz of oil over 3 days. There is engine oil dripping down the passenger exhaust, and the exhaust bolts are dripping with oil. The skid/crossmember between the engine and tranny are thoroughly oil-drenched too. The driver side doesn't have a leak.
The valve covers were caked over in grime, so I cleaned them up and ran a rag around the gasket. I didn't find any leakage that would lead to this much oil dripping onto the exhaust. There is also some oil resting on the bottom of the passenger side of the timing cover.
The service records show the oil was changed about 1k ago, and it seems like the engine is at least a half-quart overfilled. The receipt has a note of a leak at the rear of the oil pan, but it actually doesn't appear to be leaking from there, and a pan leak wouldn't explain oil dripping from the exhaust bolts.
I'm hoping excess oil is just being shot out somewhere as opposed to say, a rear main seal leaking. Is this a common leak?
I'm about to drive this thing 2k miles so any help would be greatly appreciated.
Here are some pics:
