Returning Idle Problems

[CLINNVIP]

Whats up guys,

First off I have a 86 325E swapped with a M20b25 by the PO.. It has an XG motorsports chip the PO put in. I have been going through his work and have corrected and replaced A LOT, but I cant seem to shake the idle wonders I have been having. I've read around the forums but cant seem to find the answer I'm looking for..

Onto the story, The car had been operating fine but has always had a rough start up since PO swapped the motor. When its cold it idles just below 500 rpm roughly then as it warms it will oscillate from 500 to 1000 rpm's and then finally settle its idle at around 800 after 15 min or so and drive perfectly normal.

Yesterday driving home from work my car starting hiccuping and stalling as I added throttle and when I dumped the clutch to keep it alive the rpm's spiked to 3K and stuck. I reengaged the clutch to bring the idle down but it merely stalled out. Fortunately, I was rolling downhill so I used the clutch to jump start it again.

This morning I replaced the chipped DME with a stock DME and on the drive to work the same darn thing happened! As I parked I shut it off and tried to start it but would not turn over. Ive replaced the ICV twice and cleaned both units, cleaned my CPS(yesterday and today), I also have checked my vacuum lines and everything seems to be okay, also checked my motor to chassis grounds bc I just replaced my oil pan. Has anyone had any symptoms similar to these? Any suggestions or help is appreciated!

UPDATES:

After I finally got the car started and drove home the same symptoms happened. Drove fine for a few minutes and then my idle rose to 3K. Once I got home I let the car sit at idle. It slowly started to decline and eventually sat at 1K and never went further down.

I have not been able to get my car smoke tested, but I have been trying to eliminate the possibilities. When I start the car it runs super rough and idle oscillates. After about 5-10 min the idle rises up to 2800-3000 RPM's and stays there. When I apply throttle it chokes it out and the RPM's drop significantly and it tries to adjust but simply rises back up to the high idle issue.. Hopefully this explains some common symptoms of whatever problem I am having?

[Tonybeemer]

Have you checked fuel pressure ??

[dnguyen1963]

Do a smoke test to eliminate any vacuum leak issues before troubling yourself with other components. Looking over vacuum lines/hoses is not the way to say that you have no vacuum leaks.

[CLINNVIP]

@dnguyen Agreed, lol definitely will do. Do you think that this is the only culprit? What suggests the high idle of 3K rpms?

[E30NJ]

Did you check the PCV hose line running to the valve cover?

[dnguyen1963]

@dnguyen Agreed, lol definitely will do. Do you think that this is the only culprit? What suggests the high idle of 3K rpms?

After you fix all vacuum leaks, you need to disconnect the negative cable from the battery for about 1 min to reset the ECU. Your idle should then return to normal. You might need to drive around for about 20 min for the ECU to adapt to the new settings.

[603Racing]

Things that can cause bad idle:

• Vacuum leak
• Ignition (any of the ignition system, but in this case I doubt it's ignition)
• AFM
• TPS
• ICV
• CPS
• O2 sensor
• Coolant temp sensor
• ECU
• Fuel pump
• Fuel filter
• FPR
• All the wiring between all of the sensors and ECU

The list is extensive. The first thing to do is a smoke test. Then check fuel pressure at idle speed and off idle speed. If all of those come back good, then start testing all the sensors. There are threads on proper voltages and resistance, you will need to test at the sensor and/or at the ECU.

[CLINNVIP]

@603Racing Thanks for the list! Super helpful!