Low Idle Speed And Engine Vibration

[Ian_J]

I have just bought a very low mileage (20,000 miles), one owner, 2005 1.6 vvti Corolla. The car has been main dealer serviced from new and has just passed the MOT test. The previous owner is a family member, hence I know that the history is genuine. I have had a good look under the bonnet and it the car does appear to have been serviced well (e.g. clean oil at correct level, clean Denso air filter)

In general the car runs very well and feels 'spot on' to drive. The one problem I have is, that once warmed up, the idle speed drops to around 600rpm (and hunts up and down a little). It doesn't stall, but there is a level engine vibration which I doubt is as Toyota intended. It feels very much like the engine is simply idling at too low a speed. If I switch on the air con or the head lights, the ecu correctly increases the idle rpm and it idles smoothly.

I am aware that in the last few years the car has covered very little mileage and has probably been on very few journeys of more than 3 miles. I am suspicious that something may be 'gummed up' due to the engine never realy having got properly warmed up and only being driven once or twice a week very gently.

Since buying the car, a week or so ago, I have driven it every day, including one 100 mile trip at motorway speeds. The low idle speed and accompanying vibration has not improved, as I had hoped it might given a bit of 'proper use'.

I would appreciate help with the following questions;

• is the idle speed of 600rpm when warm correct? (seems a little low to me)
• if this idle speed is too low, can someone recommend where I should start looking for the cause
• if this idle speed is correct, can someone recommend where I should look for the cause of the vibration
• is it worth filling up with 'super unleaded' in order to 'clean' the engine (if so is there any particular brand that is recommended)?

[oldcodger]

They do idle around the 600 - 650 rpm mark and can feel a bit lumpy when ticking over

Typically if its idling and you have the door open you can see the door vibrating, as someone else mentioned.

Its there on mine, but just got used to it.

Not aware its causing any problem or if there is a cure as expect its all set by the ECU.

If you have had the Battery disconnected, then for the first few miles the ECU has to re-learn and then the idle really does drop to almost zero and then jumps back up etc.

You may also notice another quirk of these systems is that when , say you come to rest a traffic lights, foot off the accel, the rpm does not drop instantly, sometimes falling slowly over a couple of seconds.

I ran on standard Shell for 2 years and then on Asda petrol for the last 3 years, noticed no difference in mileage or performance, still get around 42 in summer and 38-40mpg in winter.

There are many petrol addatives on the market, such as Cataclean, Redex etc etc, but if its just got though the mot emission test ok and mpg/performace is good.....

[Ian_J]

Thank you oldcodger for your response to my query.

It sounds like the low idle speed is just part of the Corolla's character. Mine also has the 'quirk' you describe where after stopping at a junction it takes a few seconds before the idle rpm falls from around 900rpm to 600rpm.

[roks]

Yep... soon as it drops below 700rpm, I get that vibration on mine too, while it hovers between 600-650rpm.

I tried supporting engine from the oil pan with a block of wood to thinking it may be the engine mounts, it made not difference.

I just live with it by applying the theory, "its not a fault, its a feature".

[Ian_J]

As an engineer, over the years I have come to the conclusion;

• if something operates in a manner that you didn't expect then it's an opportunity
• if you can't fix it, it's a feature

I will go along with the response from roks, that the low idle spend is simply a feature and I will get on with enjoying driving the car.