Idle hunting issues

[bmwsun]

Hi there. I am trying to diagnose an issue on my wifes e30
1989 325i Auto around 250k but car engine has been rebuild.

Issue is that the when i am driving the car and i come to a stop the idle drops around or below 500 and feels like it wants to die. It seems to hunt as well like it may surging but it doesnt go above 750rpms.

Here is what i have assess so far:
1.) Replaced ICV to no avail
2.) replaced O2 sensor with known good
3.) checked for air leaks


Next step:
Check connection/resistance of crank position sensor...

anything else i may be missing......

Thank you,

[4doorE30]

barometric pressure sensor i read up on some things people have replaced them and it idle smoother like it should

[bmwsun]

Hi there. I am trying to diagnose an issue on my wifes e30
1989 325i Auto around 250k but car engine has been rebuild.

Issue is that the when i am driving the car and i come to a stop the idle drops around or below 500 and feels like it wants to die. It seems to hunt as well like it may surging but it doesnt go above 750rpms.

Here is what i have assess so far:
1.) Replaced ICV to no avail
2.) replaced O2 sensor with known good
3.) checked for air leaks


Next step:
Check connection/resistance of crank position sensor...

anything else i may be missing......

Thank you,

Checked the crank position sensor and it is good.

As well i swaped the airbox with a known good (no resolution)

I checked the TPS and i am unsure of the readings i am getting, however i did notice that when i took the plug off it has some fluid in there and i aware that over time oil can drip onto the TPS and damage it.... should i just replace it?

[agent]

Last week I fixed a warm idle issue by replacing the breather hose that connects the intake to the valve cover. It was only after removing the old hose that a big split was discovered on the underside where it makes that sharp turn to attach to the intake assembly (just below the ICV).

It had some hairline cracks visible on the top, but a carb cleaner spray-down vac leak test did not reveal it as being the culprit. When my neighbor pressed his thumb firmly on that hose against those cracks, the car would warm start (without adding throttle), which is something it would not do unassisted. In hindsight, apparently he was applying pressure in just the right way to help seal that big split.

Pelican has the hose for $3. I bought the same brand (Eleplast) from my local CarQuest for $10 because I could get it that day - I am impatient.

[jlevie]

I checked the TPS and i am unsure of the readings i am getting, however i did notice that when i took the plug off it has some fluid in there and i aware that over time oil can drip onto the TPS and damage it.... should i just replace it?

The TPS contains two switches, one that closes at idle and the other that closes at WOT. The respective pins on the connector should be open circuit when not at idle or WOT and zero ohms when activated.

I always drill a 3/16" in the center of the bottom cover of the TPS to give the oil that will seep in from the intake a place to go.

[txtorquemade]

The TPS contains two switches, one that closes at idle and the other that closes at WOT. The respective pins on the connector should be open circuit when not at idle or WOT and zero ohms when activated.

I always drill a 3/16" in the center of the bottom cover of the TPS to give the oil that will seep in from the intake a place to go.

Good idea. Ill do that when putting my 90 i back together next week.

[bmwsun]

I disconnected the battery and reset the DME and it made no difference. my next step is to throw in a spare ecu i have...will update as i go on.

[tim88325is]

Replace or test the coolant temp sensor for the DME.

[Sir Smirnoff]

Did you check your spark? It could be that. For our FSAE car, the timing was off and it always idled rough because of it. Sounds like an ECU/tune issue. does this happen when cold , warm or both??

[bmwsun]

I just replaced the coolant temp sensor and it runs fine now (knock on wood). I was looking at the sensor and it appears that i my have broken as a was able to move it from side to side (twisting motion)