Car wont hold a steady idle... UGH!

[cscracker]

Have you checked for vacuum leaks? They're extremely common, as there's a lot of different places they can happen. Check all your rubber hoses (don't forget the one going across to the crank case), intake boot, and brake booster vacuum lines, but also check where the aluminum fittings go into the throttle body - they're just friction fit, and when they get old and worn, they stop sealing. You can also leak vacuum out the dipstick tube, it's got a rubber hose holding it to the oil pan, as well as the O-rings on the dipstick itself.

[Kershaw]

I would have said a vacuum test too, but he said he had a smoke test done.

[wilholl]

Have you check your throttle position sensor (switch)?
Make sure the switch is closed at idle position.
Also, check for water and corrosion in the fuel rail injector harness plug
This fixed my idle problem.

[Simmie]

I was having a similar surging idle issue along with intermittent trouble starting. Both problems were fixed by replacing the spark plugs.

[blackmist27]

Here's a picture of mine:

http://pics.deadface.org/phone/e30/IMG_20160813_202552.jpg

This is taken from the passenger side, the blue one is the one for the ECU, brown one is for the cluster. My car only has two sensors, and the other two holes have plugs in them. Your car has four sensors in the thermostat housing, so I'm not sure what the other two are for.

Something else you can try is using the wider end of the spark plug gap spec. Using a gap at the wider end can help an unsteady idle as well. I use NGK ZGR5As and they are factory gapped to the wider end. Never had a problem with idle since I made the switch to them not long after getting my Eta.

hmm... id love it to be that simple. who knows? ok... ill buy some and give it a shot :)

Have you checked for vacuum leaks? They're extremely common, as there's a lot of different places they can happen. Check all your rubber hoses (don't forget the one going across to the crank case), intake boot, and brake booster vacuum lines, but also check where the aluminum fittings go into the throttle body - they're just friction fit, and when they get old and worn, they stop sealing. You can also leak vacuum out the dipstick tube, it's got a rubber hose holding it to the oil pan, as well as the O-rings on the dipstick itself.

we did a smoke test... fixed all the leaks. at least i think we did. professionally done.

I would have said a vacuum test too, but he said he had a smoke test done.

Have you check your throttle position sensor (switch)?
Make sure the switch is closed at idle position.
Also, check for water and corrosion in the fuel rail injector harness plug
This fixed my idle problem.

hmm... this is a good suggestion. ill have to check the rail.

I was having a similar surging idle issue along with intermittent trouble starting. Both problems were fixed by replacing the spark plugs.

thanks ill check. just ordered some new plugs. fingers crossed.

[JIM1inWisconsin]

idle

Had two e30's with idle problems that were cured instantly after installing a Mark D chip that I got used for $75. Amazing. Same chip used in both cars. Not sure exactly why this worked but I'm a simple minded pragmatist and it seems you've tried everything else.

[blackmist27]

Had two e30's with idle problems that were cured instantly after installing a Mark D chip that I got used for $75. Amazing. Same chip used in both cars. Not sure exactly why this worked but I'm a simple minded pragmatist and it seems you've tried everything else.

I appreciate that. actually i replaced the DME with a SSSQuid chipped version. the car drives so much better its incredible. however didnt do much for the idle issue.

[itsonlygeorge]

If you ate doing plugs, replace the wires and distributor cap/rotor. Get good Bremi wires, not that BavAuto crap.


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[cheffy30]

surging is not good... idle control valve has a lot to do with it... pull it and clean it.
although the m20 seems to have a rough idle... mine has been sorta rough forever...
seems normal... she purrs though...
for what its worth

[RobTapps88]

Mine revs to 1500 on a cold start then once it levels out it bounces(slowly) between 700-900 as well.. Kinda drives me nuts.. Too broke to diagnose right now though. Hope ya can figure it out!

[blackmist27]

UPDATE:
so i THINK* i solved the surging problem. i replaced the sensor that sits on top of the thermostat housing that looks like a nut with 2 prongs coming off of it. my car now drives as it should. fingers crossed but i think its solved. thanks everyone!

[RobTapps88]

UPDATE:
so i THINK* i solved the surging problem. i replaced the sensor that sits on top of the thermostat housing that looks like a nut with 2 prongs coming off of it. my car now drives as it should. fingers crossed but i think its solved. thanks everyone!

Good to hear, will have to try cleaning mine.. Not going to replace it as the motor has done its time and a new one is coming in a few months time..

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