tpenta

Hey gang,

What exactly happens when you start the engine in the first couple of minutes? I usually let the car warm up until the RPMs drop suddenly from 1,100 to 800. I'm just curious what actually happens in those couple of minutes and why the RPM drop.

Thanks,

-T

jhbrennan

Since manual chokes were eliminated, every car I've ever owned on cold start has higher RPM so this shouldn't concern or surprise you. CW (and owner's manual) says start driving right after start, just keep RPMs less than 4K until engine oil is warm.

tpenta

I am not really concerned. I am curious as to what actually happens. It seems as if it's going through a process of some sort until it reaches a stable idle of ~800 RPM.

Thanks,
-T

Bob Rouleau

Warming up the catalytic converters.

ADias

Exactly, to control emissions. The ECU driven by lambda sensor (pre/post cats) readings changes mixture and revs until the emissions op params are attained. Contrary to the 'drive right away', which I think is emissions driven, I like to idle the engine a couple of minutes until the idle settles. This is not to heat up the engine, as idling is not efficient for that.

Edgy01

Just drive off. The car knows what it needs. And is ensuring sufficient RPM is maintained until the internal temps are achieved. No need to stop to idle and 'warm up' the engine.

Tsilnner

I have always waited a minute or so for the RPMs in my cars to drop before I drive off, keeping the revs under 4-5,000 'till the oil temp gets to 200. I take the time to belt-up, turn on the iPod, start the seat heater and fire up the radar detector.

I remember reading that the quick drive off advice was to keep the emissions down and that in some countries in Europe they actually have a law forbidding you do sit parked warming up the engine.

Like my more frequent (that recommended by Porsche) oil changes, I figure it can't hurt.

tpenta

Thanks guys.

-T

Quadcammer

incorrect.

The lambda or 02 sensors are not active until the ecu switches to closed loop.

In open loop, the car runs off fuel and timing tables as well as the MAF transfer function

ADias

OK. I thought the sensors worked all the time. Any particular reason it does not work in closed loop at startup?

The startup regime is still an emissions driven one, though.

stevepow

I fasten seat-belt (or did I already do that?), release hand-brake, glance at TPM and gauges, glance to see if BT and iPod have booted up to the PCM, close the ashtray cover where I removed the CTEK, push the Sport button, check the rear-view, select R, check the rear-view again, and ease it on out...

Optionally switch on headlights, set NAV, find a good XM station.

It's a lot to do...just to run to the grocery store...

Quadcammer

agree about emissions.

The 02 sensors need to be hot to function properly. Takes a few minutes for the exhaust to heat up enough.