Uneven idle on 1993 C3G Twingo
My Twingo has an uneven idle and is failing emissions because it's running slightly rich. I've changed:
Coolant temperature sensor
O2 sensor
Coil
Spark plugs and leads
IAC valve
Air filter
Fuel filter. Pump comes on fine and delivers good pressure.
I've also changed the gaskets in the throttle body. Unfortunately the car doesn't have OBD2 (I'll never buy another car with injection but without OBD2) and I don't have access to the old Can Clip diagnostic machine. There's no engine light. Checked engine block earth. The injector is clean and I checked the O-rings. I replaced one with a green O-ring, which probably isn't right for the fuel system. I'll change it. According to the new coolant temperature sensor the engine is running slightly too hot, because the temp light on the dash comes on but it's quite faint. It's only a one pin sensor and the resistance curve might not be the same as OEM.
Compression is 160-175psi on all four cylinders. I checked when the engine was cold. Vacuum is OK; drops slightly when the engine slows but still within good range according to the dial.
The video is when the car is warmed up. This is the C3G engine, not the later D7F. The idle used to stumble more than this but since I changed the IAC valve it goes up and down slowly. There's also a burble from the exhaust but no smoke. All four spark plugs seem OK.
The engine starts and runs well, apart from a slight occaisonal misfire under load at light revs. Fuel is economy is still good. These use hardly any petrol anyway so it's hard to tell.
My thinking is that there might be leak in either the intake or exhaust so I've bought a smoke test machine to check both.
Any ideas what might be wrong with it?
https://reddit.com/link/1shjumw/video/9095xd45mcug1/player
Vacuum test prior to new IAC valve installation. New test would be similar, not as dramatic a drop