This idle makes me want to blow my brains out

[foundation982]

I've had this car for about a year and have been non stop fighting the idle on it. I know it's an e28 but it is the 528e ETA engine
The idle seemed fine the whole winter right around 800 rpms but here in IL the entire winter was literally -10 to -40 outside that may have been what kept it down. Now that it's warming up its steadily risen to 1100rpm and just today it started sitting at 1400rpm and would sometimes begin to terrible idle surge going up and down very slowly.


I have been trying everything and cannot get it to steadily sit at 700-750rpms

Things I've checked/done
-All intake rubber hoses checked/replaced.
-Idle control module swapped in with a working one
-swapped in working ECU
-Rebuilt fuel injectors and O-rings
-Replaced Intake manifold gaskets and oil return O-rings
-Swapped in working ICV
-Tested TPS
-Replaced coolant temp sensors on thermostat housing
-Replaced O2 sensor
-swapped on a known working oil cap
-Replaced cap, rotor, wires.
https://www.youtube.com/watch?v=wR92kf_osk0

Sorry for the excessive revving obviously couldn't get it to do the slow idle surge on camera

[SlamedIAm]

I know you've replaced a lot of the hoses and gaskets but you really need to smoke test it to rule out vacuum leaks.

[foundation982]

I know you've replaced a lot of the hoses and gaskets but you really need to smoke test it to rule out vacuum leaks.

This is very true. I know I've been told this a couple times but the car is a heap of crap. I don't want to spend the $100 to just have a smoke test done. I live in the middle of nowhere and I'm not sure if any of the shops around here even have a smoke tester.

[dnguyen1963]

you can make yourself a DIY smoke machine for about $25. Search here or Google it. It will not be good enough to find all the leaks, but it will find all the major ones.

[jlevie]

This is very true. I know I've been told this a couple times but the car is a heap of crap. I don't want to spend the $100 to just have a smoke test done. I live in the middle of nowhere and I'm not sure if any of the shops around here even have a smoke tester.

You may not want to spend the $100 on the smoke test but that, a check of the TPS, and a check of the rail fuel pressure are mandatory diagnostics.

[foundation982]

You may not want to spend the $100 on the smoke test but that, a check of the TPS, and a check of the rail fuel pressure are mandatory diagnostics.

Have checked TPS need to do a pressure test on fuel rail still.

[NJ2.5rser]

This idle makes me want to blow my brains out

Did you try the tps sensor?


Sent from my iPhone using Tapatalk

[foundation982]

Did you try the tps sensor?


Sent from my iPhone using Tapatalk

Yep as the comment above says ^ its working as it should.

[Danny915]

With the car on take a screwdriver and tap on the icv, does idle change at all?
Also ohm out your sparkplug wires and coil, check ends on wire and cap for any sign of corrosion. Also have your valves ever been adjusted?

Sent from my SGH-M919 using Tapatalk

[jd_e30]

Have you checked/adjusted throttle cables? My bad idle was a result of both bad plug wires (loose #6) and most importantly the cruise control cable mount, which was broken. Make sure your cable is adjusted correctly! Just a thought! My idle would slowly creep up from 1100 all the way to 2-3k!

[jd_e30]

Any luck?

[jd_e30]

*jeopardy music*

[foundation982]

With the car on take a screwdriver and tap on the icv, does idle change at all?
Also ohm out your sparkplug wires and coil, check ends on wire and cap for any sign of corrosion. Also have your valves ever been adjusted?

Sent from my SGH-M919 using Tapatalk

I have tried changing the idle with that, according to the bentley it changes the resistance. It makes no difference when I change it and set the screw back in the place it was. Cap and rotor probably need to be replaced but this shouldn't cause a high idle as far as I'm aware of, however they would cause a weak spark. Valve clearances adjusted when I bought the car about 10k miles ago.

Have you checked/adjusted throttle cables? My bad idle was a result of both bad plug wires (loose #6) and most importantly the cruise control cable mount, which was broken. Make sure your cable is adjusted correctly! Just a thought! My idle would slowly creep up from 1100 all the way to 2-3k!

Checked throttle cable it should be where it's at, The cruise cable also has no tension on it, unless when the car turns on for some wear reason it pulls it haven't checked while running. I'm confused why a bad spark plug wire would cause a high idle? is the computer trying to compensate for weak spark and dumping more fuel in?

[foundation982]

I'm starting to wonder if something with the hydrobooster braking system is causing a leak. I don't have time this weekend to mess with it as I am moving to TN woo! but I will check it out when I get a chance still have a moderately high idle at 1000-1300 rpm.

[702pjc]

AFM -> IAC -> TPS

If you've checked all of those than it has to be an intake leak.

If all else fails check the ECU.