Engine Hunting on idle RESOLVED !!!

Hi All
Well I did a service on a Micra C+C which obviously involved changing the spark plugs.

After re assembling everything and starting the engine, at idle the revs would rise and drop between 1500 - 1900 revs (hunting) this would indicate a possible vacuum leak.

I re checked all my connections which looked good.
Sprayed carb cleaner ( cold engine , with CAUTION ), but there was no change in engine tone. Did the same thing with Propane gas (Safer), but still no difference.

I then did a smoke test and it showed no leaks.

So what was the fix ????

On the top of the engine to the right there is a rubber pipe about 20mm dia, this joins onto a 90 deg plastic elbow that push fits into the large rubber pipe that joins the throttle body to the MAF sensor / Air box.

Well , the elbow was pushed to far into the large rubber pipe restricting the air flow to the throttle body. I pulled it out enough so that the clip was still holding in position, started the car and ALL GOOD !!!!

The way I found this, was with the engine running i pull the elbow out and the engine smoothed out, pushed it all the way in and the idle went erratic again.

I hope this fix helps someone out as I've seen loads of posts with this problem costing some upto £700 for new TB and MAF sensors.

Also thanks to Martin for his input.

Michael
 
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