Idle keeps dropping & stalling

[TomB]

This morning the 7 had trouble starting and would stall unless I covered the throttle. It wouldnt settle and kept stalling. I had to drive a round trip of 40 miles with the car trying to stall all the time. Its an EU2 1.8k on MEMS & VVC plenum.

 

Ive reset the ECU & throttle, charged the battery and checked the connections around the throttle body but its still struggling to start and keep going. When I come off the throttle, it stalls.

 

Ive noticed the green air temp sendor was blackened with the plastic shroud melted. Could the temp sensor effect the idle?

 

Could a dying battery cause these symptoms? Or maybe a coil?

 

[mav]

Temp sensor for ecu or the iacv...

[TomB]

Is the ECU temp sensor the green one on the inlet? Any idea where I can get one in Cheshire/ Merseyside on a Saturday?

 

[Paul Richards]

Tom

Is the vacuum pipe to ECU ok?

[mav]

Rover link in Widnes will have stock.

[john milner]

I've had a sticky IACV which had the same starting problems but within a minute or two it was fine so I doubt that IACV is the total problem.

[c7trp]

I had these symptoms when the battery was dying.

 

The volt drop at idle seemed to cause the ECU to struggle to keep working. I was seeing (IIRC) about 9.8v at idle. I assume the alternator can't keep up and idle revs?

 

Easy to test - use some jump leads and a known good battery (eg from tin top 😬 ) and if all is OK warm idle wise then time for a battery.

 

Problem was worse with verniers and the lumpy idle this gives

[Silver Machine]

Had the same problem with 1600 supersport. Replaced IAVC which improved things a bit then replaced battery which seems to have cured it. New battery is not a Banner and has a bit more cranking power. Resetting the ECU can help.

[TomB]

I've replaced the battery and done some fiddling, but apart from cranking better, its worse than previously as it wont fire at all now.

 

Things Ive done:

Reset ECU and throttle several times;

Cleaned & check the IACV works - it moves and is clean inside;

Cleaned the flywheel position sensor & connection;

Checked fuses and relays under the dash - OK as far as I tell

Cleaned connections on two temp sendors

 

Observations:

Fuel pumped primes;

Smells of fuel so injectors are working;

Spark plugs were fuelly and quite sooty;

Both temp sendors had not very firm connections to the loom - they could be quite easily pulled off;

Connecting wires look very fragile into the temp sendors.

I cant tell if the TPS is working - how do I check this out?

 

Now the 7 is stranded at my parent for a good few weeks, as Im away at a wedding next weekend, Im hopefully moving into a new house the weekend after, and Ill have difficulty getting any replacement parts / sendors to try in the meantime.

[TomB]

Which temp sendor is for the dial, and which is for the ECU? There is one above No 4 exhaust manifold and one behind the exhaust cam/ rear left of the head.

[Graham King]

Tom, the brass sender with the single wire is the one for the dial, in mine it's the one above no 4 primary.

 

Graham.

[john milner]

Useful link for VVC wiring.

[TomB]

Thanks for the link. Ive decided a critical step in diagnosis is to find whether I have a spark. Tomorrow in a dark garage Ill disconnect the injectors and remove a plug and lead to see if a spark is being generated. If not, that will help me narrow it down.

[TomB]

I have a spark at cylinder 4, gradually weakening towards the front of the engine until its gone at cylinder 1 which points towards a dead/ dying coil. The dizzi and rotor arm look OK, and I have similar continuity on the king lead and 4 HT leads. A new coil is only £18 +vat from Redline.

 

Would a dying coil prevent the car from idling, and a dead coil stop it firing? I guess if the spark was weak, idling might not provide enough fuel to keep the engine going.

 

Hopefully Ill get it running before the weekend, and then look to correcting any senders or wiring which may be making it run less optimally.

[john milner]

Similar problem?

[TomB]

Well, Ive changed the coil and it tries to start, I can hear it coughing then with a little throttle it fires, but only on 1.5 cylinders. I now suspect HT leads, dizzi or rotor. There is continuity on the leads, including through the spark plugs, but could I have continuity and have failing leads?

 

I guess Ill keep changing/ testing bits to aid fault finding.

 

 

 

[TomB]

Lo and behold, it appears 1 & 2 spark plugs were dead. After putting leads directly on the coil and looking for sparks, swopping 1 & 2 with spares, it fired, ran, revved & idled with out stalling.

 

Puzzled now though:

Why/ how should two adjacent spark plugs fail at the same time? They were not more than 2year / ~ 7000 miles old.

How would this relate to the first manefestation of the stalling at idling problem?

Is it likely a combination of problems coming together at the same time such as a failing coil or poor lead connection?

Could rich running cause early spark plug failure?

 

Will change all the plugs and leads, but Id like to understand whats happended. Or is it just one of those things?