s50 swap rough idle when cold

[dillon7]

Hey guys, I'm having some issues with my s50 swap and wanted to see if I could get some opinions on where to go next. The idle is rough when cold, around 450-500 rpm, and will stall and die unless I constantly give it some gas. Once it warms up it will idle about 80% correctly, and fluctuate between 750 rpm-1k rpm. When the fan kicks on the idle will drop down to around 650 rpm, and it sounds like it's missing and the idle will be rough.

Bit of background:

The car is a 1986 325e

Did the swap a couple years ago, and it would occasionally idle odd, but the car sat for a couple years and the idle seems worse.

Before the swap, the previous owner of the motor installed the following new parts: crank seals, cam & crank position o-rings, water temp sensor, timing chain guide rails, timing chain tensioner, new thermostat & housing, water pump, ARP head bolts, main belt, spark plugs, and knock sensors.

Running a 413 red label dme with correct tune.

New MAF

Recently did a smoke test and didn't find any vacuum leaks.

ICV was clean but decided to throw in a brand new one just for safe measure along with new hoses. That didn't change anything.

Bought and installed a new TPS, no change.

I'm at a loss right now, any ideas?

[dillon7]

bump, any thoughts?

[dillon7]

Messed with the car some more tonight. I noticed that the throttle arm wasn't touching the stop screw, so I did the adjustment according to this write-up, which seemed to help. The idle was extremely sensitive to the adjustment and barely moving the screw would move the idle +/- 200 rpm. After setting it at the recommend 1/4 turn, the car would idle around 800-1000 rpm.

The first time it got hot enough for the fan to kick on, the idle went back down to around 550 or 600 and was rough, but the second and third time it only dropped to around 750, and then goes up to around 900 or 1000 when it goes off.

Still not sure what the cause of this is. I recently got new coil packs and spark plugs, but have not installed them yet. Going to try and install them tomorrow to see if that makes any difference.

If you guys have any other ideas, I'm all ears.

[ykarabala]

I had a similar issue and my gooseneck hose wasn’t clipped in all the way. I’d spray carb cleaner all around and look for increased rpm.

[dillon7]

I had a similar issue and my gooseneck hose wasn’t clipped in all the way. I’d spray carb cleaner all around and look for increased rpm.

I'm not sure which hose you are referring to. Are you talking about the one coming off of the idle control valve? If so, it's secure, and I ran a smoke test so I'm pretty sure I've eliminated any vacuum leaks.

[dillon7]

I had some time to install the new coil packs and spark plugs this evening. Fired it up and there was no change. Still rough.

I was reading about some people having idle issues and it coming from a bad coolant temp sensor. The PO of the motor said he had replaced it but since it was a cheap part and the one on mine didn't look new, I decided to replace it as well. Still no change.

At this point I'm completely out of ideas. The only other thing I can think of is that maybe I have a bad DME?

[dillon7]

Another update:

Recently did a compression test. All 6 cylinders were within about 15psi of each other, so I think I am good to go there. Do you guys think it would be worth it to do a leak down test as well just in case?

[TeXJ]

any update?