Cold start rough idle

[bchene]

Hello
I have a 96 318ti (manual) that recently began to start hard and idle very rough until the engine warms up (two minutes or so). I have reviewed the threads and am intimidated by the potential number of problem areas. Some other info on the car; has 97k miles, regurlarly maintained, no CEL light, and runs great once warmed up or during warmer weather (car is in Maine). Given all the potential issues what in your expert opinions should I investigate first.

[CirrusSR22]

Probably a sensor isssue like mass airflow meter, coolant temp sensor, or air intake sensor.

[aceyx]

When's the last time you changed your plugs? Platinums start to wear at the 100k mark.

[bchene]

Plugs and wires were changed at 90K. Only happens when cold, and does not last long, several minutes. Runs beautifully when warm. Rough idle and will almost always stall out once before settling down.

[Paul Anthony]

would a cam position sensor cause this rough idle/hard start problem?

My car runs fine in warm weather and when the engine is warmed up.

I got the check engine code recently and CPS needs to be replaced.. but the problem didn't start until the weather dipped below freezing.

anyone have any experience with this issue?

[bigdondero]

I have a similar problem. On cold start, the car starts up;immediately, the idle dips to about 150rpms, then back up to 800, then down to 150. This continues for a couple minutes. I find that if I rev to about 2000rpms for about 20 seconds, it idles fine. I think it might be a vacuum line. I will be fixing the suspected vacuum line tomorrow. I will post my results whether I am successful or not.

[bigdondero]

I changed numerous vacuum lines tonight. The problem still exists. Next thing to tackle is the fuel pressure.

[cva_mikey]

BG Induction Service + thinner oil!

Had exact same problem with my '98ti, so I had BG Induction Service performed, added 44K to the tank, and changed the oil to a 5w-30 synthetic. 17 degrees this morning, and she fired on the first crank and settled into a smooth idle.

cva_mikey

[Bills86e]

Yup. Nothing like a working IAC! On older engines get carboned up.
Clean'm or replace'm.

http://www.ebay.com/itm/B024-NEW-199...#ht_3349wt_987

The IAC is a key component to your engine's idle speed by allowing for air to bypass the
throttle plate. A bad or malfunctioning idle air control valve/motor will often cause a
variety of symptoms such as engine stalling engine stumbling and irregular fluctuation of
engine idle speeds.

Bills86e

[bazar01]

Originally Posted by Paul Anthony

would a cam position sensor cause this rough idle/hard start problem?

My car runs fine in warm weather and when the engine is warmed up.

I got the check engine code recently and CPS needs to be replaced.. but the problem didn't start until the weather dipped below freezing.

anyone have any experience with this issue?

I had a P0340 fault on my 1996 and it starts, idles and runs fine. I went ahead and bought a CPS by Beck from Advanced and my CEL stayed off.

When I changed the CPS this past few days, I removed the upper intake and put it back on When I started it, it idled really rough and almost stalled. I realized I forgot to install the vacuum line that goes to the injectors. After I hooked that up, it idled fine and there was no CEL triggered.

Remove and clean the idle control valve.