95 Corolla 4Afe: Cold Start Stall Immediate After Unless More Throttle
1995 Corolla 4AFE automatic, 200k miles.
Almost failed smog due to lean 2 months ago, so I took out the EGR with the EGR pipe for cleaning and found it to be very clean, nothing more than a very thin layer of carbon and it is all dry.
While cleaning the EGR I degreased the engine bay, mainly between the engine and the firewall, because a previous power steering pressure hose leak has caused a lot of grime in the area. I used simple green (diluted with water into 50% concentration) and rinse with buckets of water slowly poured over the engine (while avoiding the electrical as much as possible).
Now the car would start and crank, but if the weather or the engine is cold (ambient 55F or so) it would stall in idle unless I press on the accelerator for more air. If I hold the accelerator, even a slight amount, for 20 seconds or so, then the idle would stay afterward and would drive fine. I've driven as far as 8 miles and see no problem. This has repeated for over 3 days and the engine bay is now dry, all electrical parts have no sign of white powdery residue (short circuit), battery voltage is 13V at off and 14.1-14.3V when idle.
I've cleaned the throttle body's idle air control valve hole and a bit into the throttle body with Pyroil Parts Cleaner (similar to brake cleaner), the can said wait for 5 minutes if use for carb so I think it is probably safe. The liquid came out of the throttle body very black, but after cleaning the same thing happen the next day.
What else should I check? TPS sensor adjustment? IAC valve with external control? coolant temperature sensor? ECU? vacuum leak? fuel injector? As far as I know there is no CEL.
I also changed the fuel filter but that was after the cold start stalling have already occurred, and of course a new fuel filter doesn't really do anything. I changed it because it is long overdue (original) and it may help with fuel pressure and fix the lean burn.