Engine RPM at cold-start?

bluebullet · 01-18-2005, 06:17 AM

My car hates getting started in the cold. On start up is the engine rpm supposed to be around 1500 rpm or so? mine just stays around 900-1000, sometimes hitting 1100 if its cold enough. It also reeks of fuel from the exhaust. Would the air by-pass valve need cleaning or replacement? Car gets up to temp ok and is fine once warm.

ae1969 · 01-18-2005, 06:41 PM

You know.......... I can't ever recall my 944 liking 0 degree weather........and I have never seen her jump to 1500 rpms to warm up. IT WOULD BE NICE.

It hates the cold.

There are 2 things that will affect cold starts........ Engine temp sensor for the dme and air temp sensor ... If those are in spec not much else you can do. The dme will richen the mixture hence the smell of gas..... Mine jumps to ~1100 rpm and shudder do to the cold.......warms up and idles fine.

I think when they designed this series (944) they assumed that cold start would be for the florida area.

bluebullet · 01-18-2005, 07:45 PM

LOL oh well not much luck I have then.

Zero10 · 01-18-2005, 08:11 PM

You have the same problem I had.
If it was a few degrees below 0, it would stumble at idle, and the exhaust simply reeked of gas. Once we hit about 20 below, the idle would bump up to around 1100-1200rpm, but still stumbling, and reeking of gas, and once it was below -20C, the results are tainted since the car was plugged in, but again, it would idle at 800ish, and stumble a lot.

Now, here's what I did on troubleshooting.
I measured the resistance of the DME temperature sensor at 5 different temperatures, all 5 times it checked out. I measured the resistance of the intake air temperature sensor at +20C, and at -30C, and both times it checked out.

The one thing I always meant to do, but never got around to, was clean out the idle stabilizer valve.
The other problem I had, was that 90% of the time after driving, it would return to an idle after one or two dips to 500rpm. However, the other 10% of the time, it would hunt endlessly. I checked and rechecked everything, again, no vacuum leaks, all injectors were absolutely great, etc. Couldn't find anything wrong, but I still hadn't pulled the idle stabilizer valve. It was on my to-do list when the car burned, so I guess now I'll never know.

However, it's my guess for your problem (providing you've checked out the temperature sensors).

Zero10 · 01-18-2005, 08:12 PM

Oh, time for a quick addition.
I talked with a porsche tech at South Centre Fine Cars (the local stealership), and he told me that it should idle in the mid 1000 range (i.e. 1250-1750) when cold, but only for a couple minutes, not until fully warmed up.

bryanthompson · bryanthompson's Garage

When really cold (like below 10 degF), mine idles a little under 1000, like at about 900.

It actually acts the same as when my oxygen sensor was bad. It's a little rough and stumbles a little bit. So I think it could have something to do with the one-wire oxygen sensor not heating up quickly enough...?

livewirevoodoo · livewirevoodoo's Garage

Quote:

Originally posted by ae1969
Mine jumps to ~1100 rpm and shudder do to the cold.......warms up and idles fine.

that, and the overwhelmingly rich exhaust describes my ride this winter.

bluebullet · 01-19-2005, 05:11 PM

well lo and behold, I started it up this morning. The car did its normal bumble and stumble, missing out here and there (too hard to fire all that fuel), but after like 10 seconds, the idle started going up. I took quite a bit of interest in this, and looked at the tach...slowly rising to 1500, and staying there for a good 5-6 minutes or so. Car was running clean and the smell was gone.

I havent touched the car at all!. I think the idle valve might need cleaning cuse when i pulled the old intake boot off that was ripped it had all sorts of grime in it. The vacuum hose going to it is dryrotted, and prolly causing problems. Im going to see if I can get it inside tomorrow and pull it apart and replace the hose and clean the idle valve.

BTW where is the engine temp sensor on this motor?

Zero10 · 01-19-2005, 08:31 PM

Under the #1 intake runner, Since it's a late motor, there will be 2 sensors there, one with 2 spade connectors on it, and the other has a big blue plastic connector, that's the DME temperature sensor, the other one is for the gauge, one wire for the gauge, the other for the warning light.
The DME sensor has an independant ground, while the gauge sensor grounds through the block.

Sounds like the Idle Stabilizer needs cleaning.
I'll sell you a half-burned one for cleaning

bluebullet · 01-19-2005, 10:55 PM

haha i bet all the crap got burned out of it. Prolly works good as new