Cold Start Excess Revving Incident

[Manic]

Had a weird experience tonight. Started the car up for a quick food run, everything normal. It was a complete cold start so it was doing the usual hovering around 1.8-2k RPM. Let it sit like that for 10-15 seconds, and then I put it in reverse to get out of my driveway and it dropped to normal idle speed as per the norm. I had to steer around my girlfriend's car so I depressed the clutch and used the brakes a bit as I reversed around it.

However, while I was clutched in, the engine revved up to about 2.5-3k with zero throttle input. I put it in neutral and made sure I wasn't touching the gas pedal or that it wasn't caught on anything, all clear. I blipped the throttle real quick and let out the clutch, still in neutral, and only after did it return to normal idle.

I'm fairly positive I'm not imagining things because my girlfriend commented on how "it sounded weird". I've never had the engine return to cold start revs after it's been put in gear (22k miles so far) so I was little worried to say the least. No CELs or anything for the rest of drive, perfectly normal.

So, my question is, has anyone else experienced this?

[D_Thissen]

How cold was it there last night? I have had that happen to my car as well from time to time. Usually only when it was below 0C (32F).

[Manic]

I'd say probably around 40-45F. It has been a bit chilly lately.

[Efferalgan]

Is 1.8-2k idle at 40F really "usual" for your cold start? Is that NA/stock?


Mine never went above 1.7k or so even at -25C and lower (negative F). With supercharger revs might go slightly higher occasionally but my idle now is 900.

[Manic]

Originally Posted by Efferalgan

Is 1.8-2k idle at 40F really "usual" for your cold start? Is that NA/stock?

Yes, it's the usual and yes it's NA/stock. I believe this is pretty par for the course for stock engines. After it's warmed up, it idles at around 700.

[jvincent]

Originally Posted by Efferalgan

Is 1.8-2k idle at 40F really "usual" for your cold start? Is that NA/stock?


Mine never went above 1.7k or so even at -25C and lower (negative F). With supercharger revs might go slightly higher occasionally but my idle now is 900.

I think you should post a video of your RPMs at startup.

@Tcoat in case he misses this one.

[Tcoat]

Originally Posted by D_Thissen

How cold was it there last night? I have had that happen to my car as well from time to time. Usually only when it was below 0C (32F).

Me also. But again it was very cold not 45 degrees (California "cold").

Never seemed to be an issue and ran perfect afterward.

Maybe just a brief moment of ECU insanity? Wouldn't worry unless it happens a lot or throws an CEL.

[Tcoat]

Originally Posted by jvincent

I think you should post a video of your RPMs at startup.

@Tcoat in case he misses this one.

Dude, really?
"misses this one"?

[MisterSheep]

I don't know about you but I usually try letting it warm up even more than when the idle dips. Our cars idle very high upon start-up due to them trying to warm up the cats. This is a very common occurance with cars now-a-days. I let it dip from 1750/2k down to 700. It first will go down to about 1k on cold starts before it dips even more to about 700 or 600 rpms.

I know this probably doesnt answer your question but I do not know what else to tell you bud. My only suggestion would to let it warm up more before driving it. I too live in CA and we dont get anywhere near as cold as some other folks. I leave for work around 5:30 am each morning and have experienced probably 34 degree F being the coldest this year. Whenever I let it warm up in the mornings its roughly for 5+ minutes. I know we can't do this every time but it's just a good practice to get your car to warm up as much as possible on its own rather than driving it. If you must drive it just let it dip to the 700/600 before you set off. I just remember if it's revving even more then it's trying to warm itself back up.


I hope some of this help......

[jvincent]

Originally Posted by Tcoat

Dude, really?
"misses this one"?

You might have had a meeting or something.

[Tcoat]

Originally Posted by MisterSheep

I don't know about you but I usually try letting it warm up even more than when the idle dips. Our cars idle very high upon start-up due to them trying to warm up the cats. This is a very common occurance with cars now-a-days. I let it dip from 1750/2k down to 700. It first will go down to about 1k on cold starts before it dips even more to about 700 or 600 rpms.

I know this probably doesnt answer your question but I do not know what else to tell you bud. My only suggestion would to let it warm up more before driving it. I too live in CA and we dont get anywhere near as cold as some other folks. I leave for work around 5:30 am each morning and have experienced probably 34 degree F being the coldest this year. Whenever I let it warm up in the mornings its roughly for 5+ minutes. I know we can't do this every time but it's just a good practice to get your car to warm up as much as possible on its own rather than driving it. If you must drive it just let it dip to the 700/600 before you set off. I just remember if it's revving even more then it's trying to warm itself back up.


I hope some of this help......

In the real cold start world:

Start it
Let it drop from high to mid idle
Put in gear and drive it away
Take it easy for 5 minutes or so of driving to bring cats, bearings, oil and fluids up to semblance of earth like temperatures
Let er rip


The only reason I would let it sit and idle for 5 minutes or more is to allow the heater to come to temperature and blow through the defroster before tackling 1/2 an inch of solid ice all over the car.

[go_a_way1]

Originally Posted by Tcoat

In the real cold start world:

Start it
Let it drop from high to mid idle
Put in gear and drive it away
Take it easy for 5 minutes or so of driving to bring cats, bearings, oil and fluids up to semblance of earth like temperatures
Let er rip


The only reason I would let it sit and idle for 5 minutes or more is to allow the heater to come to temperature and blow through the defroster before tackling 1/2 an inch of solid ice all over the car.

^ This hahaha!!

I have a remote start for a reason

[Manic]

Very good info, all. I'll just chalk it up to an odd anomaly. I generally let it warm up to normal before taking off, but the desire for awful junk food blinded me.

As for the weather, yes us southern californians are spoiled with great weather. Unfortunately, I live in Temecula/the desert. So recently, we've had lows of around 30-40F with highs of 75-80F, which has just thrown of my internal calibration. Not enough rain to get snow, although we did have some freak snow last year.

[steve99]

Originally Posted by Manic

Had a weird experience tonight. Started the car up for a quick food run, everything normal. It was a complete cold start so it was doing the usual hovering around 1.8-2k RPM. Let it sit like that for 10-15 seconds, and then I put it in reverse to get out of my driveway and it dropped to normal idle speed as per the norm. I had to steer around my girlfriend's car so I depressed the clutch and used the brakes a bit as I reversed around it.

However, while I was clutched in, the engine revved up to about 2.5-3k with zero throttle input. I put it in neutral and made sure I wasn't touching the gas pedal or that it wasn't caught on anything, all clear. I blipped the throttle real quick and let out the clutch, still in neutral, and only after did it return to normal idle.

I'm fairly positive I'm not imagining things because my girlfriend commented on how "it sounded weird". I've never had the engine return to cold start revs after it's been put in gear (22k miles so far) so I was little worried to say the least. No CELs or anything for the rest of drive, perfectly normal.

So, my question is, has anyone else experienced this?

Heaps of stuff happens at initial cold startup

Different compensations are applied on hot start

see diagram below

On Cold start

Fueling is enriched to heat cats, fast idle and retarded timing (thats the noisy bark at startup)

Different offsets to MAF (fueling) are applied depending if in neutral or in gear.

Different idle depending on coolant temps.

If you load the engine so it drops below its idle target of say 1800 rpm in initial phase the eCU applies more compensation to try to hold the idle at 1800, so if you then depress the clutch it will idle above 1800 for a bit , before settling back to its target idle speed. It a bit like anti-stall.

Idle targets A through to I are applied throughout the startup/warmup phase depending upon time since startup I suspect and coolant temps ,probably other factors as well

Best let it idle for a minute or so till idle settles to about 1200.