With the valve train noise diminished in my car, I've been noticing other noises. One of those is a "pop" "pop" "pop" noise coming from the airbox, corresponding to slight engine stumbles at idle. I've also noticed previously that these engine stumbles seem to be correlated to bubbles at the coolant bleeder valve. Another, possibly related, symptom is what feels like backfiring around 2K-2.5K RPM. Above that RPM the engine seems fine.
I've got a new coil, new distributor, new wires and plugs.
What should I be looking for? Is this a head gasket symptom? Fueling issue?
My gut read is head gasket as it would appear that one of the cylinders has blown through to the adjoining one and when firing is pressurising the adjacent cylinder and coolant passages. Take a look at your spark plugs and see if one is discoloured or carboned up more than the others. If that fails, then do a leak down test and see if the cylinders can hold pressure. If this works, then do each cylinder individually.
Would also look at cylinder head studs and torques.
I am not an expert, but it does not sound good.
If you rev the engine a bit by hand in the engine compartment, do you see bubbles coming into the coolant fill reservoir? Hope not.
White smoke out exhaust pipe? Hope not.
Is there a lot of moisture inside the tailpipe while the engine's running? If so just touch a drop to your tongue. Sweet taste? Hope not.
No to all of the above.
Also no oil in the coolant nor coolant in the oil -- which is why I remain hopeful that it's not the head gasket. Maybe a vacuum leak somewhere?
did you actually torque your plugs?
I've checked the torque of the plugs.. they are torqued properly. The symptoms still persist. There is a smell, and some white smoke/steam at startup on cold mornings. I put the smoke down to condensation as it dissipates when the car warms up. The smell seems more like running rich to me, but I suppose it could be sweet smelling.
Troubleshooting this will have to wait until the end of January, as the car goes to the body shop tomorrow and I won't have it back until then. In the mean time I'm going to order a head gasket set in preparation and everything else needed for a head refresh. Might as well do it right..