Rough Idle When Cold

mdezie06 · 12-06-2005, 04:18 PM

Hi, Im new to the board. I have a 98 Z28 Auto. The cold weather has created some problems though. When i start it the rpms are unstable and it will sometimes die it will also sputter and shake a little bit while running. It runs perfectly after its warmed up but from a cold start the rpms sometimes drop down to about 3 or 400. Just wondered if anyone might have a clue as to what may be the cause of it.

Thanks, Matt

**PEWTER Z** · 12-06-2005, 05:31 PM

You gotta let it warm up and let the oil and motor parts heat up. There's alot of friction going on in the motor before it's totally warmed up. Mine does the same thing too.

**fredg369** · 12-06-2005, 07:14 PM

I have an LT1 and mines is does the same.....starts right up then a little shake and rpm goes up and down alittle.I hate it....makes me want to sell the damm thing.

mdezie06 · 12-06-2005, 07:19 PM

If thats the case does anyone know of anything that would help this? Or what oil would help to reduce this rough start?

**Zboner** · 12-06-2005, 07:20 PM

i also have a 98z and i have the same problem with that, give it 5-10 mins before you drive it in the mornings

**fredg369** · 12-06-2005, 07:23 PM

I'm using mobile 1....0 w40....with synpower additive.
Think I should change it out to the ...5 w30....like it recommends from gm

**~redlinels1~** · 12-06-2005, 07:32 PM

Im running mobile 1 5w 30. Ive never experienced that problem. Even on COLD ass mornings. Such as this morning when it was -1.

Question...why are using an additive with a synthetic oil?

**fredg369** · 12-06-2005, 07:44 PM

I read it somewhere on here that it works...I don't know
Think I'm gona go back to the 5w 30 and see what happens.

**SeVeReDiStOrTiOn** · 12-06-2005, 08:43 PM

cold mornings??

...oh, we had a 32er the other morning...pretty nipplely

Maybe you could install a engine warmer or something...block heater??

**Sarge** · 12-07-2005, 06:41 AM

Originally Posted by ~redlinels1~

Im running mobile 1 5w 30. Ive never experienced that problem. Even on COLD ass mornings. Such as this morning when it was -1.

Question...why are using an additive with a synthetic oil?

Valvoline Synpower provides a shot of Moly and Boron and additional cleaning agents that makes any oil much more robust......
Sounds like your closed loop idle needs to relearn.......
From a dead ass cold start pull your PCM fuse or disconnect your negative battery cable.......then turn your key on and leave it on for a few minutes to drain all the capacitors etc. Replace the fuse or the negative battery post and start your car.....put a full load on the electrical system....rear defogger....A/C the works...let it idle for a few minutes then go for a drive...this will allow your PCM to relearn and should smooth things out for you....let us know....