Lumpy tick over

GrahamG · November 15, 2016

Today while stopped at the lights out of the blue the tick over became very lumpy as if firing on only four pots. Shifted into neutral but no improvement until I revved it hesitatingly to 1800rpm. The car had been running normally for about twenty minutes beforehand and drove normally for another twenty minutes.

It was just at one set of lights the lumpy tickover occurred.

Floored it from 30mph and it accelerated impressively. Car starts from cold as it should. Run it on premium fuel and three months ago it had major 120,000 mile Lexus service [car has done 85,000 and has full Lexus sevice history] which included new plugs.

No warning lights are showing.

Any guesses as to what might cause a one off event like this?

Tinonline · November 15, 2016

Hi

annoying as it could me a range of serviceable part issues from 02 sensor to your elbow. Might be a coil on plug issue they play up when warm and usually under gentle use 30-50 mph. They'll misfire on tickover. On some cars they won't throw codes. Doubt it though.

if you have a local indie you'll save hours fretting/testing...check for codes. Might be a sensor out of range.

I'd see if it returns though.

GrahamG · November 16, 2016

Thanks for an excellent reply Simon. I knew it could be multiple causes but it is comforting to have two culprits that are not megabucks.

Drove it another half hour and no recurrence.

I see you are in Berks, do you know of an indie somewhere near me in Fleet Hants, otherwise it is a visit to Lexus Guildford?

Tinonline · November 16, 2016

There must be an indie about but I'd use my Jaguar indie who works on all manner of classics. Fenn Motor Works in Reading.

ive done most stuff myself so far.

brendangeorge · November 17, 2016

Hi Graham

I hope you have an electrical or sensor problem mate - electrical problems usually manifest at high speed not low speed.

I have a lumpy tickover or death rattle as my wife calls it. Unfortunately she is correct - I have low compression on No 6 => duff valve or oil seal = scrap car. 60 PSI on No6 and 160 on the others.

At high revs the compression comes back up and the car runs smoothly like yours - I have warning lights and an intermittant miss fire error and other grief. At low speed an in traffic jams it is intollerable - motorway cruising I put in 4th to keep the revs up a little.

I am shopping for a new car - 15 years and 255K miles is not bad I suppose. Paying out cash for a new motor is one thing (I am a Yorshireman) bit having to choose which Lexus I get is a pain - I think it may be an RX450h.

Good luck

Brendan

Malc1 · November 18, 2016

and there's me thinking these drive trains are indestructible !

Are they on the Ls400 do you think even if they're not on the 430 ?

Malc1

brendangeorge · November 20, 2016

On 11/18/2016 at 2:27 AM, Malc1 said:

and there's me thinking these drive trains are indestructible !

Are they on the Ls400 do you think even if they're not on the 430 ?

Malc1

They are indestructible Malc - my problem was caused by some knob not tightening the plugs after a service - at least that's all I can put it down to. When we compression tested the cylinder, when diagnosing the low speed miss, all 8 plugs were only hand tight. If you treat these engines well they run forever.

I just bought a 4 year old RX450h to replace my beast. After 15 years of me it deserves a Viking funeral :)

Bren

Malc1 · November 21, 2016

OMG how on earth does an engineer service guy get that wrong .... and destroyed your car in the process. You should have had at least another half million miles in the old lady