Nissan Primera P12 dCi hunting idle & slap noise

I'm an owner of a 2004 Primera P12 2.2 dCi SVE which has been faultless until now.  It is now beginning to give me cause for concern.  The symptoms are:

1. Occasionally, it will be hard to start, taking two attempts.  When this occurs, the second attempt will result in it starting, but revving to 1500rpm, and taking a couple of seconds to settle back to 1000rpm.

2. When cold, the idle hunts +/- 100rpm.  While hunting, if I monitor the ECU's fuel rail pressure fluctuates between 15MPa and 60MPa.  After about three minutes of idling, this settles down, and the fuel rail pressure settles to 26MPa.  While pulling away with this idle hunt, the engine power appears to fluctuate.

3. After the first start of the day, a "slap slap slap" noise can be heard coming from the timing chain end of the engine, and is plainly audible from above as well as in the neighbouring wheel arch area.  At the gearbox end, it's less audible.  Having prodded around with a length of dowelling as a listening stick, I've yet to locate the source - all I can hear off the alternator, aircon compressor, aircon tensioner pully, and chain case in various positions both above and below the engine is what I'd term normal running noises - no slaps.  The "slap" occurs about once a second and is related to the engine speed.

The slap noise gradually goes away, leaving no noise after about 10 minutes.

4. No DTCs are logged by the ECU.

From reading around on the net (including here) (1) and (2) seem to suggest that I may have a problem with the fuel pump SCV.  Could this slap noise I mention in (3) also be coming from the SCV?

Many thanks.

Welcome back BAZ, have a good holiday?

rmk wrote: 3. After the first start of the day, a "slap slap slap" noise can be heard coming from the timing chain end of the engine, and is plainly audible from above as well as in the neighbouring wheel arch area.  At the gearbox end, it's less audible.  Having prodded around with a length of dowelling as a listening stick, I've yet to locate the source - all I can hear off the alternator, aircon compressor, aircon tensioner pully, and chain case in various positions both above and below the engine is what I'd term normal running noises - no slaps.  The "slap" occurs about once a second and is related to the engine speed. The slap noise gradually goes away, leaving no noise after about 10 minutes.

Having taken off the splash cover in the nearside wheel arch, the noise is a lot louder, and it seems to be coming from the crankshaft pulley... it would appear that it is the alternator/water pump belt making the noise.

If I apply some pressure (with the wooden dowel) onto the belt just before the crankshaft pulley, the noise lessens.  If I slacken off the alternator completely so the belt doesn't turn, the noise isn't present.  Re-tightening the alternator belt causes the noise to return.  Sure enough, when turning the engine by hand, you get pop/crack noises from the belt.

The belt looks fine, with very little cracking on it (it has done 60000 miles).  I guess it's just worn and needs replacement.  (As the aircon belt needs to come off to get to it, I think I'll replace both.)

I'll update again with the results of that.

On the hunting idle problem - I have a theory.  With the engine stopped, the ECU reports an airflow of 0.88g/s.  I understand that a dirty MAF sensor could artificially raise the reported airflow rate, so maybe that's my problem... certainly something to check.

Lastly, if anyone's interested in graphs of the fuel pressure, engine temperature, rpm and airflow, please PM me.  (It's a little wide to upload.)

 Great result and thanks for letting us know.