87 325is sudden high idle issue

[luiscarpenter]

Hello,
My 121k-mile M20 engine had been running smoothly for the past six months, idling around 750 RPM. This morning, it started with a steady high idle at 1900 RPM. I drove it for an hour, and the idle remained consistent with no variation. The car is only driven in fair weather on weekends, and significant work has been done over the past year to eliminate all previous vacuum leaks.

I’m familiar with the usual suspects: vacuum leaks, TPS, ICV, throttle body boot leaks, etc. Since the idle is consistently at 1900 RPM, both cold and hot (with AC on or off making no difference), where would you suggest I start troubleshooting?

[mjweimer]

1st step - check that your floor mat has not jammed against the accelerator pedal.

If no - check your throttle linkage for binding - easiest to take off the intake boot at this point

If no - electrically check the throttle position switch - remember this is a switch and not a potentiometer. If your switch is broken or out of adjustment, it will never make the "idle" position and will have high idle symptoms.

See: https://www.rtsauto.com/e30-m20-tps-...-installation/


Other than the above, there are no real influences other than the DME control of the idle air valve or vacuum leaks.

[82eye]

always start with vacuum leaks. eliminate that as a probable first. even if there is another issue, you won't be able to track it with a vac leak.

[MrBurgundy]

That's typical of no TPS signal. In that situation, the ICV is naturally wide open. Start there.