High idle when hot

[RJK91]

Hi everyone

My F4 van has an issue where the idle increases when the car gets hot and I'd like some help diagnosing the issue.

I had problems with a stuck choke cable and slack in the throttle cable. I replaced the choke cable and took up the slack in the throttle. These solved the high idle issue generally because the choke valve now opens up, but when the engine heat increases after a few minutes of running (particularly in traffic), the engine idle increases with it. The mixture seems far too rich when this is happening and it's like I'm Saddam Hussein gassing the Kurds with my exhaust gasses in traffic.

I've seen various threads about similar issues - it seems it can be due to fuel getting too hot before entering the engine and/or due to vacuum leaks. I think the engine may be getting a bit too hot generally so I'll change the coolant just in case. I'd appreciate any feedback because carburettors remain something of a mystery to me.

Thanks

 

[André4Renaults]

If your exhaust's producing too much unburnt fuel either the mixture's too rich or the sparking plugs aren't fully burning the fuel that is being pumped into the engine. Do you need to use the choke to start the car when it's cold-really cold-as it would be on a morning after the car's stood in the open overnight? If you don't, and the engine starts easily, then I'd suggest the mixture setting is too rich, since it's normally necessary to pull the choke to start a cold engine.

The problem might be in the ignition system, and a 'dying' capacitor will function correctly when cold, but will fail to function as it become hot, when the internal insulation breaks down. Perhaps change the capacitor for a new one first and see if this cures things. It'll save your hands becoming unnecessarily dirty!

Report back your findings and thoughts. I'll suggest a few other ideas if needed!