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NickbE28

BMW E28 520i 1987 manual, high idle

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Hi everyone

I hope someone can help!!! 

I've recently acquired a late 1987 520i imported from the IOM.  It came with a plethora of problems such as duff valves etc and was a non runner with only 77k.  I've rebuilt the head after it being pressure tested and surfaced,  new guides and valve seats recut etc. 

I've done the timing and so that is now right,  however the idle speed is racing away at 2500-3000 rpm. 

My big problem is that it doesn't seem to have an idle control valve which most previous posts I've read seem to blame. 

I think my fuel injection system is LE Jetronic as it does have some differences between L Jetronic and Motronic though I'm not entirely sure. Haynes was, as usual, only partially helpful. I'd be grateful if someone could clarify which system mine has. I've attached a pic to help identification.

I have replaced the airhoses as initially these were causing an issue and were goosed,  I don't believe I have any airleaks. I suspect someone has been in there fiddling when trying to get it to start or run before I bought it as there was a lot of evidence of amateur mechanics having gone on (upside down valve guide to name one) 

Can anybody help??? Please?? 

Thanks in advance. 

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You are running LE2-Jetronic. Haynes manual 1560 has the wiring diagram in section 12, page 256 Fig12.13

 

I cant tell from your photos but my old Feb 1986 520i had an idle control valve on the back of the manifold.

 

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You need to set the throttle butterfly so that it is very slightly open using the screw on the throttle body (TB). You really need to remove the TB and hold it up to the light. Slightly more is better than not enough. I think 10 thou is what you want. Having set the butterfly, set the Throttle Position Sensor (TPS) so it clicks off just as the butterfly reaches its closed position. Finally adjust the Idle Control Valve (ICV) to raise or lower the idle rpm. 800-900 is about right. There may be a cap on the end. If so lever it off and behind it is a slotted brass screw. The Throttle Damper can cause problems as well. Its function is to stop the butterfly closing to quickly when you lift off the accelerator in slow traffic. If its not working properly you will get a Lean Surge as the rpms drop too fast below idle speed and then bounce back up again. Keeping the throttle butterfly with a wider stop position helps to alleviate this.

 

Hope this helps a bit. 

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Thanks JohnH that was immensely helpful. I didn't realise that that was the idle control valve! Excuse the ignorance! It was wound fully open and seized solid in that position confirming my suspicion that someone had amateurly attempted to fix it before. I managed to exract it and clean it up enough to get it to apparently close though you can still blow through it freely. I refitted and the tickover has now dropped to 1400 rpm from 3000rpm before so a major step in the right direction! However i noticed if i crimped the top hose from the ICV it dropped to 800rpm and fully crimped it dropped to 600rpm suggesting to me that there lies my problem? Is there supposed to be anything else in there besides the big fat brass screw? I think the body of it inside may be goosed and its still not screwing in far enough or maybe something is missing?

Appreciate the help.

Nick

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You may have the water heated H valve on yours. This was for the fast idle when cold. It has a wax element and works like a thermostat, with thew air bypass hole getting smaller and smaller as the coolant heats up. They were a good idea but most corrode inside and fail leading to high/variable idle.

 

 

 

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2143296024_HValve.thumb.JPG.9aedde538cf1ace69cdc1d3aea144bc2.JPG

 

Follow Andy's advice.

 

Its also worth checking for air leaks. Easier said than done. You really need a smoke tester.

What happens when you take the filler cap off when its running? Do the revs change?

The other things to look at are the throttle cable adjusted to tight and the Throttle Damper also adjusted so it is pressing on the throttle lever to much.

 

PS, the engine s looking good to me. Nice and tidy.

Edited by JohnH

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Thanks Andy

I wouldn't be at all surprised if mine has seized, everything else seems to have! The engine was very corroded and as much work went into scrubbing that up as went into fixing the engine. I'd be grateful for that valve, How much will it be and can i PM you my address? Do you have any other E28 parts you no longer need?

Thanks JohnH

I've spent a fortune sorting airleaks, I had to go to BMW for the hoses so you can imagine what that cost! If I remove the dipstick the revs go up so i think I'm good. I've set up the throttle cable and damper and neither are affecting the idle. 

I am fairly confident that this issue lies with the idle contol valve you previously mentioned and it seems to me that mine is toast. Can you suggest anywhere i might source a replacement? 

Really appreciate the advice on this, was beginning to feel I was on my own with this!

Nick

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