Ford!

Hi Nick

As Chris says, first thing is to check for an air leak. The ECU will try to compensate for the load when D or R are engaged and raise the idle speed. When warming up this is easier as the A/F mixture will be enrichened before the system goes into closed loop so the effect of a vacuum leak is less obvious.

To rule out a transmission issue leave it in N or P and turn the steering wheel to see if this causes a dip in idle speed, then add electrical load to do the same.

Can you monitor the Lambda sensor(s) to see if they are functioning, using your scope? Does your code reader give any info on short and long term fuel trims? If it is an air leak then the system will be trying to add more fuel at idle but the effect diminishes at higher rpm.

Finally, or maybe this should be the second thing after a visual inspection, can you check the idle air control (IAC) is functioning properly. These can be motorised or PWM driven and can stick or be gummed up.

The ECU controls the idle by adjusting the IAC, altering ignition timing and A/F mixture (or any combination) to maintain the desired idle speed irrespective of load.

Hope this is of some help. Good luck!

David

As others have said first check would be a visual check of pipes and filters for something. Also check the mass air flow is clean. Be careful as it’s a delicate sensor.
Only real way to diagnose something will be to plug it in.

Where I am up to so far is a visual check of the tubes etc has not provided any clues. Throttle body seems ok. No IAC valve found. It's is very difficult to see all the areas as you would imagine. I got nothing from a basic OBD reader I borrowed. The MIL light is off. I do have an RS232 ELM scan unit which I have used on the car with some success but my laptop is now W10 so I have to see what I can do regarding software. Not easy to find something that reads Australian Ford codes properly and still works an RS232 unit! Nearest software I had before was for a Mustang which threw some spurious codes but was helpful.

After a bit of help from Mr U.Tube I have had a go at making a smoke machine. A smoke test seems to be the best way to find leaks as far as I can see. Only problem is making smoke and using it is not quite as easy as suggested. Not sure how safe the ideas are either but I now have a basic smoke chamber. Currently it leaks quite a lot of smoke but very little comes out the tube! More work required.

Just picked up my daughter in the car and had a bit of a play around with the steering AC lights etc as David suggested loading the engine in different ways. It seems to be adjusting for load ok. Then it hit me! Is the tick over really slow or am I thinking it is low because it vibrates. So about 750rpm with AC on in N, about 730rpm no AC in N, Moving steering trys to say about 720rpm with load but moves about a fair bit as you would expect. No vibration no mater what I do in N. Stationary in D about 650rpm with vibration and about the same rpm in R vibrating a lot less. So today it vibrates in D but nowhere near as much in R. Then it hit me Engine mount! What an idiot I have replaced just about every other rubber on the car so I bet it's an engine mount! Decided to order a set and see what that does first.

Thanks for your help gentlemen I will let's you know what happens with new mounts.

Nick

Good news! Cars are becoming so complex it's easy to overlook the basics and dive straight in. Some cars even go into limp home mode when they detect a problem with an engine mounting. The crabs could do this without electronics when the large mounting sheared!


How's the crab journey across the Indian Ocean going, do you get regular location updates?

David