Erratic idle
When my 2005 Ford Focus MKII 2.0 gets up to temperature the tickover becomes erratic. It idles between 1100-1200rpm, constantly moving up and down between the two. If you rev the engine, it holds at 2000rpm for a few seconds before slowly dropping back to 1100. If I stop in traffic, it will drop to 1100rpm, then rev up on its own to 2500rpm, stays there for a few seconds before dropping back to 1100. The car starts and runs fine when cold – this only happens when it’s warm. When warm, it will start and rev up to 2000rpm before dropping, and when it is turned off when warm it appears to run on slightly.
My initial thought was a problem with the throttle body. It wasn’t particularly gunged up, but I cleaned it anyway, although it hasn’t made any difference. I then replaced the throttle body, to no effect. I have tried unplugging the throttle body, then reconnecting it and leaving it for a minute to reset before starting, but this has no effect. I’ve also tried disconnecting the battery and leaving it for 30 minutes, then taking the car for a 10-mile run, to no avail.
I read the fault codes on Delphi diagnostics, but no codes are stored. I checked the vacuum pipes and sprayed penetrating fluid over the inlet manifold joints, pipework and everything I can see, but I have not found any leaks. Paul Newman
I am assuming your vehicle is the petrol version as you haven’t indicated any component that would lead me to suspect it is a diesel. As you have cleaned the throttle body without any effect, the most likely source of your erratic idling is the idle control valve. This should be located under the inlet manifold, towards the centre, and is also known as the intake manifold air control solenoid. It is secured by two screws – undo these and it may be possible to clean it using the same cleaner you used for the throttle body. I would also check that the O-rings which seal the valve are complete and have not perished, allowing a vacuum leak.
Although you have no fault codes, it would also be worth reading the live data from the ECU to ensure that the air and coolant temperature sensors are reading correctly. This is especially relevant as your problem is temperature-related. Other possible faults include the MAF sensor or a possible air leak on the manifold side of the MAF sensor, which may not be easily detected. Thanks for the prompt reply. Sorry, I forgot to say it was petrol.
Since I contacted you, the situation worsened. Under hard acceleration, a red light with the message ‘Engine systems fault’ appeared on the dash. This cleared when I turned the ignition off and back on. Diagnostics showed fault code ‘P2135’. This reoccurred several times over the next few days.
At the weekend, when driving under load, the red light and message appeared, but this time the engine management light came on and the vehicle went into ‘limp-home’ mode. I tried stopping and restarting, but within a few hundred yards the same problem reoccurred. This time it was showing fault code ‘P2110’.
I was still convinced it was a vacuum issue and, after an hour of searching, I found a one-inch split in the pipe from the PCV to the inlet manifold – you can barely see the pipe behind the manifold. I sprayed some brake cleaner on the pipe to degrease it, then used a long screwdriver to smear sealant over the split. I have been running the vehicle like this for three days and it seems to have resolved the problem. I have ordered a new pipe from Ford and – fingers crossed – this should cure the fault.
I hope this helps anyone else with a similar problem. The diagnostic codes are misleading, but at least a £40 rubber pipe and half-a-day of fitting isn’t that expensive! Paul Newman