V6 Engine Lumpy At Fast Idle

[MrT]

Has any other V6 owner experienced a lumpy feeling to the engine when slightly revving it under no load? At normal idle ~750rpm it is perfectly smooth but at fast idle ~1500rpm, such as when first started when it is cold, it seems a little lumpy. I feel the lumpyness through the car, the exhaust note is normal as in no misfires.

 

Under any load, including just putting it in Drive, it again is perfectly smooth.

 

Could this be something to do with the Auto as you are not supposed to run the enginer at high speeds in Park?

 

There are no faults at all reported on the engine management system, including a zero misfire count when measuring live.

[Ivor_E_Tower]

It's not good to run the engine at a constant speed under no load, especially when cold. This could just be a quirk of the cold idle programme, to keep the idle speed varying by a few hundred rpm. Has it always done this?

[Dally]

MrT

 

I get exactly the same thing but some mornings it seems fine. I have asked the garage to look at it twice but they say no faults are being logged. I also get what seems to be a miss fire when accelerating at motorway speeds on the odd occasion but again no fault is logged.

 

Of more concern to me recently is when in Drive and the vehicle is stationary, I am getting a slight grating/grinding noise from the engine bay. If I take it out of drive and put it back in drive, the noise dissappears. However, if I move off again in drive and come to a standstill, the noise reappears. It can get intrusive at times.

Have you experienced anything of this sort?

[MrT]

Yes the engine has always done this, and I am probably just being cautious as the vehicle is coming to the end of its lease and I am going to purchase it as long as there are no major issues in the next two weeks.

 

I don't deliberately rev the engine, the engine management system does it for me when the engine is very cold. It actually starts at a very low idle then after about 20 sec it goes to fast idle then it drops back to the low idle after about two minutes. When it is doing this the exhaust is as if a choke on an old fashioned car was in use. Incidently if I put on the heated screens, lights and air con at this stage the roughness seems to go.

 

I don't get any grinding noises, but if I am in a hurry to go off and put into drive when the engine is at fast idle, it will drive off at more than walking pace unless I keep the footbrake hard on. Are you sure the grinding noise is not the handbrake? At fast idle and in drive, if the handbrake is not hard on, the car will edge forward and the rear brakes creak as the car edges forwards, particularly so if the car has been left in the wet overmight and they have a rust coating.

[Denis]

Mr T, my car shows the same thing, a lumpiness when idling at cold though as the rev counter remains steady I have assumed it is just a characteristic of the engine/ transmission.

[Dally]

Mr T

 

The grinding noise definitely is not the brakes. If I let the car crawl under idle, the noise disappears - just seems to be there while stationary in drive.