idle out of control help plzzzz

[Manni198]

Hi i have recently bought a e30 cabriolet it jas a 325i lump in it. My problem is that it is constantly revving between 900 and 1900 rpm occasionally at a constant of 2000 rpm. Now ive been reading a fair bit about what it could be icv tp. Now i have tested these parts with a multimeter and the icv was not giving any resistance so sourced another icv. Still revving badly. Changed the throttle position sensor for a second hand one still no luck. It could possibly be the fact that both second hand parts are nackard. When i disconnect the tp sensor the car holds its revs at a constan once plugged back in again they start jumping. Now if i diconnect the icv loom nothing happens and the car still revs badly. So now i have hit a brick wall could it possibly the ecu?

[Grrrmachine]

Have a good read of this, and click on the blue links to learn more about each component:

http://www.e30zone.net/e30zonewiki/inde ... ake#Idling

[Manni198]

I have read this and have still had no luck.

[Grrrmachine]

So what air leak checks have you done?

[Manni198]

I have checked the breather pipe from the rocker cover to the carb checked tje tjin black pipe on the inlet manifold and the pipes conecting to the brake servo is their anymore

[Grrrmachine]

if you read the Wiki, it explains all of them especially the rubber cap on the bottom of the throttle body.

[Manni198]

Rubber cap?

[Grrrmachine]

Rubber plug:

http://www.e30zone.net/e30zonewiki/inde ... #Air_Leaks

[Manni198]

Ok were is this plug i have the throttl housing off

[Manni198]

Ok their is no rubber plug on the bottom side of the throttle control valve. The icv is functioning correctly. The throttle position sensor is functioning correctly. All have been tested with a multimeter so now what I have done is manually closed the gate in the icv and disconnected it so now idles ok.mis my ecu gone? I have checked the loom to the ecu to make sure the wires are ok from their to the control switches. All is okay. I can only track this to the ecu but before I buy another one has anyone got any other thoughts on this matter.

[Grrrmachine]

Ok their is no rubber plug on the bottom side of the throttle control valve.

You've either got a rubber plug, or a pipe going to the carbon canister (for cars with catalyzers). If you have neither of those, then you have a metal pipe coming out of your throttle body which is one massive air leak. I can't explain it simpler than that.

[Brianmoooore]

If the car idles OK with the ICV blocked off, then either the throttle butterfly stop is incorrectly set, or air is getting in by a route which it shouldn't.

[Manni198]

Ok their is a pipe their which goes straight into the throttle body from the underside. That is ok and have double checked all vacum hoses again.

[Manni198]

It onlu idles okay with the icv set accordingly. Opened up a little

[Manni198]

It onlu idles okay with the icv set accordingly

[Grrrmachine]

If the ICV is definitely closed, and your engine still idles, then you have an air leak somewhere.

[Manni198]

So basically if i cover the air inlet on the filter box the engine should stall

[Grrrmachine]

Guaranteed - you won't have an air leak the size of the normal air inlet anyway. Even if you had a leak, covering the inlet would restrict 90% of the incoming air, which would stall the engine.

Have you done what the Wiki suggests, and sprayed carb cleaner around the intake hoses?

[Manni198]

So basically if i cover the air inlet on the filter box the engine should stall

[Manni198]

Yes i have tried that. Could the air inlet manifold gasket be the problem?

[Manni198]

Just to update it was ecu that was causing problem. The way I figured it is if the icv has gone straight to open position when the ignition is on then this is in theory telling me that the engine requires the full amount of air through the bypass section. It obviously doesn't. I've sort of learnt how the icv works electronically so it was getting a constant open signal and not variating. I managed to find someone to let my try a ecu they had kickin about. Tried and soughted. Although I have now learnt that my throttle body and possibly the maf housing/box is of 320. Are their any advantages to this. And how can I make sure about the air box/maf

[Manni198]

Thanks for ur help grr machine

[Grrrmachine]

Is this new ECU from a 325i as well, and did you give it ten minutes at idle to learn its settings? If the answers are "yes" and "no" then there's a chance your idle was cured by overfuelling rather than an actual "fix".

As to the other thing; E30s use an AMF rather than a MAF. Small difference, but it'll help you when it comes to searching for problems. The 320i and 325i do use different AMFs, but I doubt you'll see a difference between them unless you're really pushing for performance. I had a 325i MAF on my 320i for years with no ill effects.

Oh, and don't thank me, thank Brian; he's the one with all the correct answers

[Manni198]

Ok so should I replace the ecu for a like for like? The one I got from a friend was from a 325. The nackard one had a part no. Finishing with 164 the replacement finished with 163 do I need to find a 164. I also found a little

[Manni198]

Ok so should I replace the ecu for a like for like? The one I got from a friend was from a 325. The nackard one had a part no. Finishing with 164 the replacement finished with 163 do I need to find a 164. I also found a little sticky on 325idle this would of helped me a great deal first. My bad for lack of observation. Anyhow I have learnt this car still also has the 320 throttle body so is the ecu right for this car. The was log booked as a 320 but the previous owner put a 325 lump in it.

[Grrrmachine]

The nackard one had a part no. Finishing with 164

This means that you have an engine running Motronic 1.1

I also found a little sticky on 325idle this would of helped me a great deal first. My bad for lack of observation.

The Sticky in this forum is about Motronic 1.0. It's a surprisingly different system to 1.1, and you can read about the differences here:

http://www.e30zone.net/e30zonewiki/inde ... c#Versions

the replacement finished with 163 do I need to find a 164.

164 is for a 325i, 163 is for a 320i. Internally they're the same computer but they have different chips for the different fuelling requirements.

Anyhow I have learnt this car still also has the 320 throttle body so is the ecu right for this car. The was log booked as a 320 but the previous owner put a 325 lump in it.

If you've got an engine with a 320i throttle body and 320i AFM that says 320i on the log book, and which runs better with a 320i ECU than with a 325i one, then I'd be asking serious questions about whether the engine is actually a 2.5 litre lump.

[Morat]