Car engine magically refuses to stall - how?

I drive a seat exeo, manual transmission, that is around 4 years old. When driving at v low speed in 1st or 2nd gear, it has this facility to maintain engine revs and forward motion without any gas. Like you’re crawling along in traffic, start to think about dipping the clutch as you expect the car to come to a stop, but you don’t need to and it continues to chug along without any input.

For an emphatic example of this behaviour, I was driving into a car park yesterday going v slow, 2nd gear and doing less than 10 mph. Clutch out, no gas, I drive round to a large ramp going up to the first storey of the car park (marked with a sign saying 8% gradient), and without touching the gas we drive all the way up the ramp (about 100m long).

I’ve never driven a car with this feature, so it seems weird to me - is it a common thing? The engine management system must act in some fashion to prevent stalling - anyone know what is happening?

I don’t know if there is any engine management system involved, but I doubt that is the case because all the manual transmission cars I’ve owned have been able to do this. In fact, this is how I teach friends and family to drive stick shifts: shift the car into first gear and (without adding throttle) have the drivers slowly engage the clutch. If you do it gently enough, the car will not stall and in fact will slowly accelerate.

For the record, the cars I’ve done this in have ranged from 1.5L four cylinder engines to 3.0L sixes. I have noticed it’s much easier to do this with torquier engines.

I agree with dofe. Every manual transmission car (6 total) I have owned could do this. This is also how I teach people to drive a stick.

For anyone else wondering what a “seat exeo” is.

Never heard of the automobile manufacturer SEAT (originally “Sociedad Española de Automóviles de Turismo”) in my life. Some ignorance fought today. :smiley:

Most computer-controlled engines will tolerate momentary reductions of RPM far below what is sustainable - think of older engines dieseling on after shutoff. You can turn the key back on and they’ll rev right back up.

Some clutch slip may be involved as well, with the engine continuing to spin as fast as it needs even dragging against the clutch plate.

Modern cars have closed-loop idle control, so actually open the throttle valve (or a small auxiliary throttle valve) to prevent stalling.

Older cars, motorcycles, etc. typically just have a stop screw on the throttle valve, giving a fixed opening. This severely restricts the available torque, as well as not very stable idle RPM.

What kind of engine does it have? It looks like according to the wiki, they either come with a turbodiesel, a direct-injection gas turbo or a regular old port-injected natural-aspirated gas engine. I’m guessing the “normal” gas engine is mostly a fleet engine, so I’ll bet you’ve either got the TDI or the DI gas engine. Either one of those are going to be a lot more tolerant of being lugged around at lower RPMs without stalling than a normal port-injected car.

Thks all - it’s a 1.9 VAG group TDI engine.

I’ve owned one of these engines before and it wasn’t as noticeable - appreciate that a modern car will move forward if you gently let the clutch out, but driving up a hill with no gas seemed unusual to me (I won’t be making a habit of it).

Seats are quite popular in the UK - they’re cheap versions of Volkswagen / Audi group cars, sometimes directly re-badged. Same engine and chassis but won’t be designed / finished to the same standard. The exeo I have is basically an Audi A4 from a few years back.

That right hand pedal controls the butterfly valve , which controls air flow.
The computer then sets the amount of fuel to add to it,100% control over the injectors.
Also the computer sets the ignition timing for gasolene engines… The computer got the knock sensor saying "I’m knocking " and so timing retarded to 0 TDC … without a knock sensor system it cannot adjust to the low RPM… it knocks… the explosion before the power stroke stops the engine.
But anyway the idle isn’t “0 gas” is it , so the engine slows down to the level of power “idle” is …

Over here, where ‘stick shifts’ are the norm, many driving schools use small diesel powered cars. They teach drivers to do slow manoeuvres (three point turn, reversing round a corner etc) by leaving the engine to idle and allowing them to concentrate on steering and observation.

This is fine, and gets them through the test. Then they buy a cheap low powered petrol engined car, and wonder why they can’t do that anymore.

It is all about torque at low speed.

? Don’t all cars idle at high enough RPM to move forward in first or second gear? If the engine is engaged in second gear, and you release the accelerator, you mean cars will slow down and stall?

Remember we are talking stick shifts. Yes, many cars, especially those with smaller engines will stall if you just take the foot off.

Same here, and that’s how I learned (and teach) stick as well. I guess I’ve never driven one with a small enough engine that it’s been a problem. (I learned on a diesel, which has a lot more power at the low end/torque, but the last two cars were a 1991 Nissan Stanza and a 2004 Mazda 3. Then again, it seems to me that even the smallest engine cars that are sold in America are quite a bit more powerful than the small engine end of the European market.) I’m not sure I ever experimented in second gear, but it in first they only stalled if you touched the brake with the clutch out.

I’ve only ever driven small manuals, and none have ever stalled when I release the accelerator when in first or second gear. In fact, I think even in third gear, it’ll keep on moving and not stall.

Cars being able to propel themselves along at idle revs was the main enabler to the Ghost Riding* craze of a few years ago.

Ive never owned a car with so little torque it would stall if you gently let out the clutch in the lower gears. Even the 1.0L (and 1.3L) engines in the Minis I drove in my youth had enough torque to do this.

(which, to summarise was a driver leaving the car in gear and then getting out of the vehicle, leaving it to drive along on its own until jumping back in again. I’m sure YouTube is full of examples).

Vaguely related: I once got a BMW stuck in snow on a slight incline. Realising I wasn’t going anywhere I got out to asses the situation. Amusingly I saw I’d accidentally left it in gear, because the rear wheels were slowly spinning on the snow as the engine chugged at idle revs.

Heck, I’ve idled along at a crawl in 1st, 2nd, or 3rd in a Freightliner Century.