V8 Lumpy Idle and Stalling

[OllieG]

Hope someone can help with this:

I've got a 2004 4.2 V8.. Here's what happened..

I've just filled the car in the local petrol station, then driven in stop start traffic for about 20 minutes and all seemed well.
Parked up to go shopping and returned about 10 minutes later.
On starting the car the idle was very lumpy and then as I tried to pull away the car stalled.
It took me several attempts to get it restarted and it then when I finally did it immediately stalled.

On about the 6th attempt I managed to start it a keep it running, then driving round the carpark a few times it seemed to be running well enough to get it back to my office.

There's no warning lights on and the temp gauge is bang in the middle.

After parking up and leaving for a few minutes I tried restarting and although it started first time the idle is very rough and needs some throttle to prevent stalling.

So, any suggestions on what the problem might be (and whether I'm risking damaging it by driving it 50 miles home tonight)?

Ollie

[OllieG]

An update on this;

I've had my local mechanic have a look at it.. Obviously it started fine and didn't misfire for him!

Diagnostics recorded a misfire on 1, 3, 5 & 7

He's suggesting it might be a blockage in one of the cats that's now moved.

Does that sound like a reasonable theory?

[andypryce]

Misfire on one whole bank of cylinders sounds like either fuel supply issue or electrical issue to that cylinder bank to me, don't really know enough about catalytic converters to say if they could be the cause, but seems a bit unlikely to me.

Others with more expertise can advise I am sure.

[J44EAG]

Right,

Here is how I would approach this.

Immediate new fuel filter unless a new one has been recently fitted. If the old one has a high water content, crud and/or low flow, then this could easily be causing lean fuel mixtures and misfires. Investigate fuel tank contents if water is present in the fuel filter. There was at one time also an issue with fuel tank fuel pumps. The pump filter sock would sometimes drop off into the tank.

I would also remove the MAF sensor from the lid of the air cleaner box and check for a blackened and oil covered hotwire. It should be sparkling clean. Use spray carb cleaner to remove deposits.

Check tightness of all air trunking jubillee clips and make sure the prt load crank case breather pipe from the NS rocker box cover to the air trunking is clear of muck and sealing well at both ends of the pipe.

Use one can of Cataclean to one quarter of a tank of fuel. Halfords stock it. Drive for half an hour around town. This stuff works well and can clean converters out very rapidly. Repeat again if you notice some difference. Recommended product.

In my experience, cylinder heat temperature sensors can cause big issues after 80k miles has been covered. Erplacement is an easy job. Use only a genuine sensor..cost around £26. These sensors can really mess up the way a car drives if they are starting to or have gone duff. If your car has done more than 80k miles then the sensor should be regarded with extreme suspicion as a well known issue.

If you take off the black engine cover, the throttle body is at the back of the engine bay. Excercise the electrical plug on the throttle and clear any corrosion found.

The fact that the misfires appear to only affect one side of the engine does give something of a pointer. Perhaps a problem with the wiring loom plug or cables on that one side. Cat failure is unusual. However, Lambda sensor failure is not. I`d be looking at Lambda traces with either a Torque Pro app linked via an ELM 327 blue tooth chip and an Android or Iphone. The £90 iCarsoft 930i diagnostic tool can also help with real time data logging. Flat lineing Lambda sensor certainly show up well with the Torque app. PTJS1 and I were able to condemn one of my post cat Lambda sensors recently using the cheap Torque app.

Try some of those ideas and come back to us. I`d say get a Terraclean done which can be most beneficial but given the one side of the engine issue, I don`t think that is the way to go yet.

Occasionally the big multiplug on the Power Train ECU can get corroded up. Many pins will be found on the ECU. A little corrosion there can cause havoc.

See how you get on.

Mike K

[Montana5]

Before you go chasing your tail and throwing loads of money at it, think logically...was the car ok when you drove into the Petrol Station !!

Bad Fuel.

Doug.