Help: Erratic idle when warm

[Luciano36]

Hey guys,
I've been having a problem with the idle of my 91 325ic.

When the car starts cold, the idle is super smooth; however, after a couple of minutes when engine gets warm, the idle becomes erratic. The car responds fine when you add a little throttle or on the road.

The car seems to be idling low at times after it warms up, it stumbles and tries to get back to a normal RPM (never goes high revs when idling), and I can feel the car "shaking" when that happens (at every stop light, for instance)

A little bit of maintenance history: I recently (May this year) replace timing belt, thermostat, dist cap and rotor, all plugs, water pump, rocker seals, breather hose, and adjusted valves and put a new valve cover gasket. Last week, I replaced the O2 and coolant temp sensors and cleaned the ICV.
My problem still persists.

What do I do next? Any thoughts?

Thanks a lot in advance!
Aloha

Luciano

[davem]

Hey guys,
I've been having a problem with the idle of my 91 325ic.

When the car starts cold, the idle is super smooth; however, after a couple of minutes when engine gets warm, the idle becomes erratic. The car responds fine when you add a little throttle or on the road.

The car seems to be idling low at times after it warms up, it stumbles and tries to get back to a normal RPM (never goes high revs when idling), and I can feel the car "shaking" when that happens (at every stop light, for instance)

A little bit of maintenance history: I recently (May this year) replace timing belt, thermostat, dist cap and rotor, all plugs, water pump, rocker seals, breather hose, and adjusted valves and put a new valve cover gasket. Last week, I replaced the O2 and coolant temp sensors and cleaned the ICV.
My problem still persists.

What do I do next? Any thoughts?

Thanks a lot in advance!
Aloha

Luciano

Replace intake manifold gaskets, water temp sensor and all other vacuum hoses. Sounds like your air/fuel ratio is messed up when your car is in idle mode due to vacuum leaks/and(or) bad water temp sensor.

[Luciano36]

Replace intake manifold gaskets, water temp sensor and all other vacuum hoses. Sounds like your air/fuel ratio is messed up when your car is in idle mode due to vacuum leaks/and(or) bad water temp sensor.

I already replaced the water (coolant) temp sensor last week. If I understand correctly, a vacuum leak may make the car idle higher than normal? If so, this is not the case because the car never idles higher than normal. It goes from normal to lower and then normal again (this happens in maybe 2 or three seconds) and so on.

I checked all vacuum hoses and they are in great shape. Any other causes of this? Bad cat? Wires? Clogged injectors?

[Luciano36]

Found out something annoying, but promising. I unplugged the O2 sensor and the erratic idle (when warm/hot) disappeared! With the O2 sensor unplugged, the erratic idle goes away and it doesn't seem to idle high (my tach is dead). The O2 sensor is NEW!! I replaced it last week! WTF? What's going one here?
Please help!
Thanks in advance
Luciano

[Luciano36]

Bump for help!

[Luciano36]

Somebody in another forum suggested I should check the TPS, which I haven;t done yet. I'll do it soon.
What about the purge valve? If that's faulty it will make the car idle poorly right? How can I test it?

In addition, I also found that the Motronic in the glove compartment buzzes when the ignition is on (similar buzz to that of the ICV). Is that normal??

Thanks in advance!

Luciano

[custom e30]

throttle position senser, sounds just like my prob about 6 months ago, i replaced everything, and in then end it was the throttle position sensor

[Luciano36]

throttle temp senser, sounds just like my prob about 6 months ago, i replaced everything, and in then end it was the throttle position sensor

It's good to know. Hopefully that's what causing all the idle problems. I'll check it asap and let you know. Thanks!!

[spiDmang]

keep us posted! im having similar issues

[g.ruff561]

I had similar issues. Changed the same things as you and checked for vacumn leaks. Idle was surging from 500 down to 300. Pretty soon I was driving with both feet just to maintain idle. Changed TPS and now my idle is pegged at 750. With or w/o ac. Smooth as shit. Thank you shout out to Diego and Blunttech.

[harold30]

Somebody in another forum suggested I should check the TPS, which I haven;t done yet. I'll do it soon.
What about the purge valve? If that's faulty it will make the car idle poorly right? How can I test it?

In addition, I also found that the Motronic in the glove compartment buzzes when the ignition is on (similar buzz to that of the ICV). Is that normal??

Thanks in advance!

Luciano

buzzing dme or icv when switching on means they're working and this is normal.

this is the guide i used when hunting my idle issues:

http://www.verrill.com/car/idle/e30_idleproblem.shtml

(i did everything in the link and the last thing i did was cleaning up the ejectors and replaced o-rings, idle and hard start problem solved)

also, there's a thread that has similar issue with yours try to search it and look what jlevie suggesting. it's very thorough.

[Luciano36]

Thanks a lot guys!! I'll tackle all that this weekend!
Aloha!

Luciano