Low Revs and Fuel Smell

[Ian]

This received from Judi, one of our members. Can anyone help?

My Y-reg Bongo suddenly developed erratic running with the revs dropping dramatically at idle or when braking. Our local garage (not Mazda specialist) found it to be running very rich. They replaced the spark plugs, checked the idle control valve, lambda sensor, ignition timing, and for vacuum leaks. In the end, they replaced the air flow meter and I collected the van yesterday after a lengthy absence. However, the problem is not resolved. Even at idle, the revs are unstable, hovering up and down between 800-1500 rpm. The engine is audibly running erratically and there is an obvious fuel smell.

As the garage seems to have exhausted their ideas, I feel rather stuck. Do you have any suggestions as to the likely cause?

I’m located in rural West Wales and our mechanic options are somewhat limited.

Thank you in advance for any thoughts you may have.

[g8dhe]

Do we know which engine it is V6 or 2l?

[Judi&Bertie]

H Geoff. It’s a 2L petrol automatic. Thanks to you and anyone who can help.

[g8dhe]

Looking at the engine manual a lot of the unstable idle speed faults relate to the Idle Speed Control (ISC) system starting from the ECU on pin 2W which should be between 10volts and battery voltage.
Another possibility would be for the Throttle sensor to have an intermittent problem, either in the wiring or on the track inside the sensor itself. There have been quite a few reports of damaged sensor tracks over time, usually only finally tracked down when the track finally goes open circuit rather than when its intermittent.
Another possibility might be the Idle Switch itself or its wiring?
Looking at the engine manual fault chart for the FE-E there are a lot of possibilities for this type of problem Probably a case of working thru each possible area (likely a lot have been covered in the work already carried out). Pages 138 thru to 188 in the engine manual covers the problems for the FE-E engine.

[Judi&Bertie]

Geoff, thanks for your very thorough reply. I think we need to go back to the garage with your suggestions and find out what remains to be done. Our Bongomeister wondered whether the lambda sensor might be the cause- it has only been ‘checked’ not replaced (if you or anyone else has a view on that, it would be good to hear). But thank you again.

[g8dhe]

The Lambda sensor can't be ruled out totally, the manual has a lot of ticks covering many different areas of the engine. Its often the problem with intermittent faults/symptoms because as soon as you start altering anything your never totally sure if its actually affected the problem or just the intermittency! The actual engine manual https://bongoland.co.uk/product/bongo-w ... lumes-1-2/ whilst not cheap, its a lot cheaper than a couple of hours of your mechanics time! I tend to use mine a lot and leave it open/marked on the passenger seat when I take it into a garage for actual mechanical work, and despite their protestations that they don't need it its picked up a surprising number of greasy thumb prints