Idles rough and drives jumpy when cold

[1.2gees]

I would appreciate any ideas as what might be wrong with my car, when I turn it on the first thing in the morning, my car runs rough, and idles at 900, meaning the idle does not increase. In fact, now that I think about it, I don't remember my 944 idling at a different speed than this, EVER! Also before the car is driven 1-2 miles there is a slight jumpiness to it, though I'm not sure somebody else would be able to feel this. There is no lack of power. Anybody have any ideas?

[lm6y]

The idle is normal at 900. Remember, the DME unit controls all of that. It will advance or retard the timing, increase the injector pulse width ( increasing the pulse width makes the mixture richer, acting as a choke ),or decrease it if warm, to maintain the optimal fuel ratio AND idle speed.
The jumpiness is probably the DME unit adjusting the timing when cold. If you advance the timing when cold, it will cough and sputter, so the DME will retard it enough to maintain drivability.
Imagine trying to do this all by yourself. If it weren't for the DME, we probably wouldn't want to drive these cars at all.

[1.2gees]

The idle doesn't go up at all, it might go down by 50rpms or so, but it will not go up at all, shouldn't it go up a little, my prelude used to go up to 2500rpms when cold. And the vibration is not that bad, it's just annoying. It's not the motor mounts, and it goes away as soon as ANY amount of gas is applied!

[lm6y]

The idle won't go up at all. If it's 100 degrees or -40 degrees mine idles at 900, and always has. With the DME there is no provision for fast idle, and no need for it. Like I said, the DME takes care of ALL that, so there is no need for a choke or fast idle.
Bad mtor mounts will be rough at idle, and smooth out when you hit the gas. If you are having the clutch put in, I would have him check the mounts, the pass. side goes first because it is right by the exhaust manifold, and the heat it creates. When I replaced mine, I didn't think they were that bad either, until I pulled the pass. side out in two pieces!

[1.2gees]

Thanks for the replies!

[This message has been edited by 1.2gees (edited 03-21-2000).]

[Pilot_951S]

Definitely check the motor mounts
If you have a bad mount the air flow meter will not read air correctly and that will cause a rough idle.

[1.2gees]

I have new mounts, and they're the updated style, I just cannot beleive the idle should not go up at all...Maybe I should've said it runs rough when cold rather than vibrates.

[jody]

You do not want to here this, but it sounds like bad motor mounts. That what my car did!

[1.2gees]

Ok, the car/engine is completely perfect and smooth as a babies bottom after about two minutes of running, right after the temp gauge starts moving...If you still think its motor mounts let me know or anything else that comes to mind.

[zeus]

I had (have) this exact same problem on my 1987 924S. I replaced the motr mounts which helped with the vibration at idle problem, but also had the rough idle when cold issue to deal with. I replaced the oxygen sensor which I had heard could sometimes be the problem. This did not help. I've exhausted my capabilities as a mechanical luddite and the rapists at the porsche shop said they'd have to try and track the problem thru the system.$$$$

Essentially, after looking like a complete jerk while the car sputters and coughs to warm up, it runs fine.

Having difficulty recalling the conversation I had with a mechanic but I want to remember Fuel Sending unit? There is a valve somewhere that alters the fuel/air mixture when cold.

Help me out here list members with experience with these issues....

[lm6y]

Hey guys,
I just remembered something. When the car is cold, pull the distributor cap off, and check for moisture. Mine did this and even left me stranded. Pulled the cap off and dried it out, and it ran fine. Replaced the cap gasket,and haven't had a problem since.
BTW, Zeus, how goes it with the sunroof?

[thamlin000]

My 83 944 used to run harsh and jerk under acceleration when cold. Once warm, it ran nice and smooth. Recently, it failed my state's emissions test and the so the garage where it was tested cleaned out the throttle body and (I think) the air flow sensor. That cost about $110.00 and now my car runs perfect when cold.

[thamlin000]

My 83 944 used to run harsh and jerk under acceleration when cold. Once warm, it ran nice and smooth. Recently, it failed my state's emissions test and the so the garage where it was tested cleaned out the throttle body and (I think) the air flow sensor. That cost about $110.00 and now my car runs perfect when cold.

[1.2gees]

I cleaned off my throttle body, I'll try the air flow sensor, thanks for the tip.