Sudden Surging Idle

[gonomo]

I am selling my 325IX this week and was planning on showing it today. This car has never let me down and always ran very well. Naturally, I went to start the car to meet the buyer and the idle began surging from about 1000-1800 rpm. I drove the car earlier in the day and it was fine. When I crack open the throttle a bit, the car jumps to about 3 or 4 thousand RPM. My ICV is a year old and the switch has the correct resistance, I have no vacuum leaks as far as I have checked, and my throttle position switch is working and in spec. What are other possible causes?? Thanks Sent from my iPhone using Tapatalk

[e30vert]

Throttle Body Elbow and/or the band clamps that hold it in place and make a seal Its easy to miss micro cracks in that sucker.

[cheffy30]

try blasting out the icv with brake parts cleaner. sent from hell using tapatalk

[gonomo]

Is there any way to test the power going to the icv? I have a feeling it is always open even though the ICV is good. Sent from my iPhone using Tapatalk

[tomstin]

The best all in one place document I have found in here: http://www.verrill.com/car/e30_idlefaq.shtml

[ForcedFirebird]

100% vacuum leak. When air is introduced between the AFM and throttle, it causes and oscillation as it's "trying" to keep a steady idle and bouncing back and forth between cells in the chip file. Easy way to test is when the car is surging, just as the idle drops to where it should be, unplug the IAC and the car will magically stay there.

Only way to accurately test a vacuum leak is a smoke test.

[gonomo]

100% vacuum leak. When air is introduced between the AFM and throttle, it causes and oscillation as it's "trying" to keep a steady idle and bouncing back and forth between cells in the chip file. Easy way to test is when the car is surging, just as the idle drops to where it should be, unplug the IAC and the car will magically stay there. Only way to accurately test a vacuum leak is a smoke test.

My car dies when the IAC is unplugged. I did replace it with a new one. I have a new intake elbow and the press fit vacuum lines are not leaking either. Could my air flow meter have gone bad? I feel like it’s an electronic issue because it happened so suddenly. The throttle body gasket and intake seals were all done a year ago too. Sent from my iPhone using Tapatalk

[ForcedFirebird]

Something is definitely wrong if it dies when unplugging the IAC. I have done it thousands of times to demonstrate this exact issue.

Try revving it to about 2000 as you unplug it and see if that makes a difference. The IAC should be moving in relation to the RPM.

The AFM "may" be bad, but it doesn't cause an oscillating idle like a vacuum leak does.

[gonomo]

Update: I did a smoke test, and as I thought, there were no leaks. I also tried tricking the AFM that there was less air going into the car, therefore leaning the mixture, and it idled better. I have a feeling I’m looking at a new ECU Sent from my iPhone using Tapatalk

[gonomo]

I’m almost 100% sure that this is an ICV issue. I had someone else start the car while I modulated the idle air with my hand so I could look into the ICV. The ICV stayed about 75% open no matter what the throttle position was. It’s an 88 IX so I don’t have a idle control module. Is that operation controlled in the ECU?