swapped the o2 sensor

[Erick]

Hey guys I just swapped the o2 sensor in my car in hopes of fixing my unstable rpms. My ECU also showed that the o2 sensor had a problem.

So I swap everything, crank it up, and the unstable RPMs are still there. It's not something that goes on, but it oscillates 2 or 3 times and it goes to 600rpms.

Is this just the o2 sensor getting used to the car or something? I want this damn car to stay flat at 600rpms when I'm in idle.

Edit: also, I checked the ECU and after I press the pedal 5 times it doesnt flash at all anymore. I take it that it assumes nothing is wrong then.

[Erick]

Alright it's back to it's old usual state of unstable RPMs......

Guess it's not the o2 sensor causing it. I can't find any vacuum leaks anywhere from the airbox to the throttle body. Maybe a gasket? :? Kinda doubtful, but I dunno what else to think of.

It's not the ICV, I swapped that with the alpineweiss's unit. Maybe the ECU? The weiss has the 525 and I have the 173 so I cant really swap it out.... I'm definetly not paying for a new ECU based on a guess.

Any thoughts guys?

[KenC]

What about the ICU?

[Erick]

What about the ICU?

ICU? By any chance are you talking about the Idle Control Valve ( maybe you mean unit? )

Are you talking about that black little cylinder that is connected to the intake boot on one side and the intake manifold on the other? If so, then yeah that's what I swapped out of my father's 325i. His car still ran fine and mine idled like shit.

[KenC]

If I meant 'Idle Control Valve' I would have written 'ICV' LOL.

The ICU, or Idle control unit is in your glove box by the ECU. Yours is probably green with yellow. It's about 2" x 2". They tend to overheat after a while and stop working.

[Erick]

yeah I was pretty sure you didnt... wasnt aware of a ICU though. I'll take a look tomorrow it's 12:30am right now and I have a Pre-Cal test tomorrow.

I'll see if I can swap it out from the white 325i and see if I get any results out of that. Any more ideas just keep 'em coming.

Thanks for the help Ken. I'll let you know how this works out.

[KenC]

The ICU that is all green (with yellow on the bottom) is supposed to be the best one to use. I've heard that they don't have a heatsink inside for heat dissapation so they'll burn up after a while or in really hot weather.

[Erick]

really hot weather.

Pfft..... they are hopeless in FL then. :roll:

[chesster6969]

I thought ICU's where only in older cars without Motronic.
Prove me wrong please :oops:

[James Crivellone]

M20B25's did not have an Idle Control Unit, Nor did M42's

[chesster6969]

M20B25's did not have an Idle Control Unit, Nor did M42's

Haha! Built into the DME itself.

How about running some Sea Foam through your engine. Maybe some bad carbon deposits.
Have you checked if you cat is clogged? I got a slightly better idle when I replaced my stuffed up cat.

[KenC]

M20B25's did not have an Idle Control Unit, Nor did M42's

Haha! Built into the DME itself.

How about running some Sea Foam through your engine. Maybe some bad carbon deposits.
Have you checked if you cat is clogged? I got a slightly better idle when I replaced my stuffed up cat.

I second that notion. Definitely run an entire can of sea foam through your vacuum hose. And then put an entire can in your fuel tank just before you fill up.
Have you checked for vacuum leaks in the small vacuum hose from the intake manifold to the fuel pressure regulator?
If you car has been running rich for a while (perhaps due to a faulty O2 sensor) your cat *might* be clogged up.

[EVOIIIM3]

You might have a intake leak, bad base Co setting, or a unstable crank trigger.

next thing to check would also be the TPS, make sure it clicks at idle.
Unplug it and see what happens.

[AdamF 88iS]

A good size vaccuum leak on an M20 will set an O2 sensor fault every time. That's where I'd look.

[Erick]

wow my car just gave me a huge scare today. I went to school. Left school went eat at Subway. When I started the car at subway, the check engine light was up already and when I gave the car gas the engine just went back to idle!

If I pressed ANYTHING over like 1/4 way of the gas ( or if I went pass 2k rpm ) the engine would go back to a poor idle at 400-500. It never shut off, so with a lot of struggle I could get it off the parking lot.

After 5 minutes running the engine picked up and came back to normal, but WTF?! I followed the Bentley's instructions ( although they are brief about it.... 1 paragraph on how to replace it... makes it seem like a common sense swap, no tough issues )

I just home and I'm letting the car cool down. The ECU again points at 1-2-2-1 as a fault. The o2 sensor in this case. I seroiusly think this ECU has issues.

I'll stop by NAPA auto parts see if I can find this Sea Foam or anything that resembles it. I cant afford to leave the car rotting in my garage while I wait for parts through the mail.

I'm reading the Bentley here and I"m also going to check the o2 sens. heater relay, which is right next to the AFM.