'90 Camry 3S-FE compression issue

[E_S]

My '90 Camry 4-cylinder looks like it's low on compression on cylinder #3. I can easily hear it when turning over the engine with the starter, it "skips" a beat. The engine will idle on 3,5 cylinders - if I pull the spark plug cable on #1, #2 or #4, it will really start missing at idle, but on #3, the difference is very small, barely noticeable.

When driving, it will run smooth on all 4, but below 2000 rpm under load, it will start uneven missing.

Haven't gotten around to doing a compression test, but everything looks like the #3 is low or dead, but high enough compression to "catch up" when raising the rpms. I've double checked the timing belt, and plugs/wires/cap are all brand new.

If the engine is bad, it looks like it's time for the final retirement. A shame, with spotless interior and new clutch, but the body is more or less rusted out (although not on the underside, only wheel arches and doors) and it's just not worth the expense of any major engine work in that rotten body shell..

Any known issues with the 3S-FE and compression?

[E_S]

I tried investigating a little bit. Cylinder #3 compression is low (almost nothing), and squirting oil into the cylinders does not change anything. I've experienced this before on an Audi, it had a bent valve causing the loss of compression, but the "gap" was so small that compression did not escape fast enough when the engine was running a little faster, and the cylinder fired like normal.

The Camry seems to have the same problem. Cost of parts is low, so I'm tempted to first pull the cam cover to see if I can find a valve lifter sitting lower than the other ones - which in turn is a sign of something wrong, obviously.

Two questions:
1. The timing belt was one tooth off when I bought the car. This won't damage anything, but the person doing the change could have done something else weird.. Is the 3S-FE, despite of being non-interference, capable of bending valves due to excess carbon buildup if the timing belt breaks or someone messes up the crank/cam timing?

2. Are there any known problems with broken valve springs or other problems with the valves/valve train?

[71Corolla]

If the engine sounds normal (besides the miss) then I doubt the valve spring is broken, but it could be weak (which would be rare). I'd say most likely is they drove the car with the timing off and it burnt a valve. I don't remember hearing of anyone damaging the engine when the timing belt broke, the 3S-FE seems to be pretty much immune to this.

You could try Seafoaming the engine to dislodge carbon that might have built up due to the timing being off. Just be careful when Seafoaming you can bend connecting rods if you suck in the liquid too quickly. If that doesn't help, then the only solution is to tear into the engine to see what's up. Your thought on pulling the valve cover to observe the height of the valves is a good one, do that first.

edit - if you pull the valve cover, do a valve clearance check. You don't have to be precise, just see if there is some clearance.

[drifting1O1]

i wood say it is time for a cinder leek down test ,