No power off idle, not a vacuum leak

[Earendil]

I cannot get my friends M20 working right. The symptoms are general lack of power, but the biggest thing is the hesitation off idle. Problem with idle is if the RPM is not up around 2500 to 3000 the engine really bogs down when the clutch is released.

Here's what I've done so far:
We did a smoke test which revealed no holes except for a slight bit of smoke coming out of the charcoal canister. It was a pretty thorough test too, as I started getting smoke out of the exhaust manifold which we knew had a leek, and was fixed that same day. I was sure this was going to be the problem, now I'm a bit lost.
Due to a clogged catalytic converter, we recently had that replaced.
The throttle position sensor appears to be working correctly.
Air filter looks good.
Spark plugs all look good.
The engine revs to redline relatively smoothly, there are no dead spots so I don't think it's the airflow sensor.
The fuel filter isn't more than a year old.

Thoughts? Could this be the O2 sensor? The O2 sensor was replaced a year ago, but since then with the cat dying and a different engine problem I suppose the O2 sensor could be dead. However there are no codes.

When my engine starts acting like this it's usually because I've sprung a big intake leak. But since that doesn't seem to be the issue here, unless the charcoal canister is not supposed to have smoke leaking out of it, I'm not sure what else it could be. Help!

[jlevie]

See your other thread. The engine does have an intake leak because the evap control valve is bad. As a quick check for other problems would be to disconnect the valve from the TB and plug that nipple.

[Earendil]

See your other thread. The engine does have an intake leak because the evap control valve is bad. As a quick check for other problems would be to disconnect the valve from the TB and plug that nipple.

Thanks, I saw the other thread. Based on the quantity of smoke in the leak on my own car, and on his, I don't think this is the entirety of the problem. I was blowing smoke like I set the engine on fire from the rear of my valve cover, I'd my car was running 10x better than his. His was just...oozing. Still worth giving a shot and see how much clears up.

With the hose from the canister to the TB clamped, the fuel tank should still vent, right? I guess I'm not exactly sure why it's plugged into the TB with an electronic gate, though I understand the intent of the canister attached to the fuel tank.

[jlevie]

The valve is there so that there will not be an intake leak. I don't remember the exact specs on the valve activation, but I think it only opens for a bit when the engine is at part throttle and above 2500rpm. That will pull any fuel vapors from the charcoal canister into the intake where they'll be consumed.

With that hose plugged the tank is still vented via the bottom of the charcoal canister.

If the smoke test was done properly (2-4psi of smoke pressure) there should not be any smoke leaking anywhere from a properly sealed engine/intake. Any smoke seen corresponds to an intake leak that needs to be fixed. Remember that several small leaks add up to a sizable leak. Repair as indicated until there is no smoke seen in the test. Start with a new evap valve, new valve cover gaskets and the four bungs.