Honda Car Forum

My daughter's '93 Accord LX, automatic trans, has been suffering idle hunting for some time and I got around to checking it out. Coolant is still bled, PCV valve is nearly new Honda part. I cleaned the throttle body and the EGR valve. Today I got serious, and I found the engine will idle at 1100 rpm even if I cover the throttle body intake altogether. There is a big leak but I can't find it.

The idle smooths out if I spray a bit of carb cleaner in the intake, so I tested the areas around the IAC valve, thermo lift valve and start valve with carb cleaner. Theoretically any problem with those valves just causes them to suck air through the intake, and that is not where the air is coming from. The PCV hose and even the brake booster hose can be unplugged without affecting the idle, and blocking those does not help. The Mity-vac tests on the visible vacuum hoses is good, and a visual inspection of the intake manifold shows nothing.

What am I overlooking?