Engine Idle problem 89' iX

[e30Prestige]

I posted a video on here not too long ago about a cold start throttle/idle issue. I'll cold start the car and give it throttle to move it. It will respond normally but when I lay off the throttle the car almost falls flat on it's face and sounds like its about to stall. It hasn't stalled yet but I'm sure I could get it to if I tried hard enough.
I thought I narrowed down the issue before as there was some dry rotted hoses and a bad sealant job around the brake booster hose going into the tb and the other hose that goes from the tb to the ICV.

So far I've done the following:

-Cleaned and and then ultimately replaced the ICV (This seemed to help maintain a stable idle)
-Replaced hose from FPR to back of instake
-Replaced intake boot
-Replaced hose from connector under tb to charcoal canister
-Replaced hose from tb to the top of the valve cover
-Replaced hose from ICV to tb

I've sprayed carb cleaner at suspected areas with no increase in rpm's so it leads me to believe that nothing is leaking.

So now I'm wondering what gives? Bad AFM? Connector below Tb gone bad?

I can repost the video if anyone wants to see but I'm hoping someone has some valuable input.

Thanks in advance!

[Seawolf]

Does it only do this when cold ? How's it idle when at running temp ?

- and how does the car perform when driving aside from the idle problem ?

[e30Prestige]

It only does it on a cold start. Besides that it runs pretty good when its up to temps. Idles at around 900-1000 which is a little higher than I'd like but I'm not sure how to change that. Could be too much tension on my throttle cable.

Does it only do this when cold ? How's it idle when at running temp ?

- and how does the car perform when driving aside from the idle problem ?

[Seawolf]

Okay, that high idle could point to another vacuum leak.

But just to eliminate a couple of other candidates:

Bad coolant sensor (the blue plug with 1 brown & 1 brown/red wire). The sensor should ohm out at 3500-4000 Ohms cold / 330 ohms at operating temp.

Bad continuity from the coolant sensor brown/red wire to pin 45 on the DME. Maybe a bad C191 connection there, C191 is the round plug & socket under the intake manifold. If the sensor itself checks out you can perform the same ohm tests between pins 45 & 24 on the DME, you should get the same readings.

Note the sensor is the rearmost of the 2 plugs and should be light blue on the thermostat housing, the brown front plug is the sender which just drives the temp gauge.

[e30Prestige]

Okay, that high idle could point to another vacuum leak.

But just to eliminate a couple of other candidates:

Bad coolant sensor (the blue plug with 1 brown & 1 brown/red wire). The sensor should ohm out at 3500-4000 Ohms cold / 330 ohms at operating temp.

Bad continuity from the coolant sensor brown/red wire to pin 45 on the DME. Maybe a bad C191 connection there, C191 is the round plug & socket under the intake manifold. If the sensor itself checks out you can perform the same ohm tests between pins 45 & 24 on the DME, you should get the same readings.

Note the sensor is the rearmost of the 2 plugs and should be light blue on the thermostat housing, the brown front plug is the sender which just drives the temp gauge.

I replaced the easiest to reach sensor... I think it was the brown one not too long ago. I haven't replaced the other one because it was semi hard to reach. I'll test it out and come back with results.

[Dave_G]

I replaced the easiest to reach sensor... I think it was the brown one not too long ago. I haven't replaced the other one because it was semi hard to reach. I'll test it out and come back with results.

The brown easy-to-reach one just sends a signal to the temperature gauge -- it has nothing to do with how the engine runs. The one you want is the harder-to-reach blue one, which is the coolant temp sensor that sends the signal to the ECU. You may need to pull up on the plastic rail that connects to the injectors. You won't break anything. It'll just pull up off the injectors, and when you're done you can snap it back down.

[e30Prestige]

The brown easy-to-reach one just sends a signal to the temperature gauge -- it has nothing to do with how the engine runs. The one you want is the harder-to-reach blue one, which is the coolant temp sensor that sends the signal to the ECU. You may need to pull up on the plastic rail that connects to the injectors. You won't break anything. It'll just pull up off the injectors, and when you're done you can snap it back down.

Sounds good! thanks for all of the awesome info! I will report back with the outcome!