Carrera 3.2 continued emissions / idle misery...
Posted: Mon Aug 23, 2021 3:16 pm
I've been fairly thorough by my standards in trying to fix this - does anyone have further suggestions where to go next?
SYMPTOMS / SIGNS:
Carrera 3.2 Emissions fail, CO reading is circa 5.5% should be around 1% I think. MOT limit is 3.5% or 4.5%. The car sometimes idles fine and other times fluctuates up and down wildly.
FURTHER INVESTIGATION AND FIXES:
-Car runs and drives beautifully apart from rough idle. Fuel economy good. Burning a little oil.
-Car apparently has oxygen sensor deleted
-I thought inlet manifold gasket was leaking, so the manifolds have all been off and the gaskets replaced. I'm confident it's all sealed nicely now, but the problem remains.
-No apparent vacuum leaks
-Cylinder head temp sensor apparently working fine: 250 ohms on hot engine, climbs as engine cools
-Air temperature sensor apprently working fine - 1,400 ohms on a hot day
-AFM potentiometer within acceptable range - 250mv closed, 4v wide open
-Idle valve apparently working: I removed it and plugged up its vacuum hoses, leaving the wires connected. Raised and lowered engine idle using the throttle bypass screw and the valve could be seen to open and close as it should with rising and falling revs. Also, it responds correctly to 12V on each of its positive terminals.
-HOWEVER: If I just disconnect the cable to the idle valve, the engine stops hunting. It idles perfectly. Reconnect it and the engine hunts wildly.
Next I moved on to the idle mixture screw on the AFM. As I began to turn it I realised it was so much unscrewed it was no longer in the threaded part of its tube and it was falling out. Presumably somebody has been in before me and tried to lean the mix for the same reason as me, and gone too far. The manual talks about some special tool to turn this but on mine it just takes a standard allen key. Is this because I have a simplified air filter system?
I have been reading about others with similar problems and threads point to: a) take apart the AFM. I took it off but can't see where to start disassembling it, b) leaking FPR - replace if leaking and c) bent fuel return line. Any further suggestions? How does the AFM come apart? Can I test and/or service the FPR? Where does the fuel return line run? There are a lot of fuel lines!
Also, this is the idle mixture screw and its home is just a hollow tube with nothing else in it - is that right?
https://photos.app.goo.gl/QnzVpahHBcF8i8EJ9
SYMPTOMS / SIGNS:
Carrera 3.2 Emissions fail, CO reading is circa 5.5% should be around 1% I think. MOT limit is 3.5% or 4.5%. The car sometimes idles fine and other times fluctuates up and down wildly.
FURTHER INVESTIGATION AND FIXES:
-Car runs and drives beautifully apart from rough idle. Fuel economy good. Burning a little oil.
-Car apparently has oxygen sensor deleted
-I thought inlet manifold gasket was leaking, so the manifolds have all been off and the gaskets replaced. I'm confident it's all sealed nicely now, but the problem remains.
-No apparent vacuum leaks
-Cylinder head temp sensor apparently working fine: 250 ohms on hot engine, climbs as engine cools
-Air temperature sensor apprently working fine - 1,400 ohms on a hot day
-AFM potentiometer within acceptable range - 250mv closed, 4v wide open
-Idle valve apparently working: I removed it and plugged up its vacuum hoses, leaving the wires connected. Raised and lowered engine idle using the throttle bypass screw and the valve could be seen to open and close as it should with rising and falling revs. Also, it responds correctly to 12V on each of its positive terminals.
-HOWEVER: If I just disconnect the cable to the idle valve, the engine stops hunting. It idles perfectly. Reconnect it and the engine hunts wildly.
Next I moved on to the idle mixture screw on the AFM. As I began to turn it I realised it was so much unscrewed it was no longer in the threaded part of its tube and it was falling out. Presumably somebody has been in before me and tried to lean the mix for the same reason as me, and gone too far. The manual talks about some special tool to turn this but on mine it just takes a standard allen key. Is this because I have a simplified air filter system?
I have been reading about others with similar problems and threads point to: a) take apart the AFM. I took it off but can't see where to start disassembling it, b) leaking FPR - replace if leaking and c) bent fuel return line. Any further suggestions? How does the AFM come apart? Can I test and/or service the FPR? Where does the fuel return line run? There are a lot of fuel lines!
Also, this is the idle mixture screw and its home is just a hollow tube with nothing else in it - is that right?
https://photos.app.goo.gl/QnzVpahHBcF8i8EJ9