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E36 M3 evo Idle problem. Problem started off 1 year ago. Car was dying out when stopped at traffic lights etc. Took car to a mechanic who told me he thought it had a vacuum leak and was also down on power. He fixed Vac leak by replacing hoses and also fitted a lamda sensor. He also fitted a new Vanos seal kit. Car came back with tons of power but now idle would start of normal say 750/800 rpm but then climb to about 1400 rpm which is obviously way too high. Blipping the throttle would bring the idle down again but it would climb again to 1400 rpm. I spoke to the mechanic who said the only other thing left would be the idle control valve which should be changed out. Car sat inside all winter and I’m only getting back to it now.
I decided to have a look myself and I removed the airbox/inlet manifold to gain access to the idle control valve. I found the following (See pictures for descriptions):

evo1.jpg evo2.jpg evo3.jpg evo4.jpg evo5.jpg evo6.jpg


(I hope these images come through as they help a lot to explain)



So started her up and went for a run to warm her up. I get the following results.
Engine warm and vacuum pipe to T piece unblocked – I can hear and feel a vacuum leak (unsurprising) and the engine idles steady at 1800 rpm – way too high
Engine warm and Vacuum pipe to T piece blocked – engine idles steady at 1400 rpm – Still way too high.
Car drives ok but I want to get to the bottom of it. Checked obvious stuff like throttle cable backed off at idle / not sticking.
Could the idle control valve be defective? – after cleaning it moved freely and rattled when twisting. I can get a new one but it’s a £180 experiment!
Are there any other vac pipes I should check that aren’t under the inlet manifold?
I’m thinking of getting codes read to see if any faults but if anyone has any ideas I’d really appreciate the input.
 

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Discussion Starter #2 (Edited)
Hi just realised these images are tiny so resending the images - hopefully it will be easier to read! Any ideas of what to try next appreciated.

My M3 has developed a problem recently with idling. Any pointers would be much appreciated - I'll go through the story to date
At first it was dying out at lights and junctions. I took it to a mechanic who said it had a Vacuum leak and was way down on power. He put vanos seals in it. He also replaced a lamda sensor. I got it back - the power was way better but now the idle speed would start normal like 750 rpm but then hunt to 1400 rpm. Blipping the throttle would bring it down but it would soon rise to 1400 rpm again. I spoke to him about this and he said the only other thing it could be was the idle control valve. The car sat inside all winter and just last week I decided to have a go at getting to the bottom of it

I started by removing the air intake box to inspect the pipes and ICV.
I found a Vent hose that connects from intake box to head was really easy to squeeze in and had signs of perishing (but not bust) I could imagine this would be restricting engine breathing under acceleration and got a new one as a precaution. See Image


for full size click link

https://i.postimg.cc/cH67bLyS/evo1-1.jpg

Next I removed the idle control valve and found a bleed-off pipe connected to the top hose was running to a t piece with one port completely open?? See image



for full size click link
https://i.postimg.cc/fb8jC0PC/evo1-2.jpg

also
https://i.postimg.cc/DZyCVpz3/icv-A.jpg

also
https://i.postimg.cc/QxRnBqfc/ICV-B.jpg

also
https://i.postimg.cc/Yq4sqPzp/ICV-C.jpg

Removed pipes and inspected ICV which has clogged with carbon deposits and not moving/clicking when twisted/flicked. Cleaned this up with carb cleaner and it moved freely


for full size click link
https://i.postimg.cc/WbZ8VzDp/evo1-3.jpg


Cleaned the inlet ports while I had access


for full size click link
https://i.postimg.cc/fRjv3Pj6/evo1-4.jpg


Before putting back together I decided to keep my options open regarding the T piece with no connection so I connected a longer hose to it that I could access without removing everything again. See image


for full size click link
https://i.postimg.cc/nhtkhx74/evo1-5.jpg

Put all back together again


for full size click
https://i.postimg.cc/BvSB2Cmt/evo1-6.jpg

So started her up and went for a run to warm her up. I get the following results.

Engine warm and vacuum pipe to T piece unblocked – I can hear and feel a vacuum leak (unsurprising) and the engine idles steady at 1800 rpm – way too high

Engine warm and Vacuum pipe to T piece blocked – engine idles steady at 1400 rpm – Still way too high but I’ve left this blocked off.

MAF - Read a bit about MAF and decided to do a test with and without the MAF connected to try and rule it out. I got an interesting result but not sure if it means MAF is suspect.

With MAF connected on cold start idle = 1000 rpm still high. Went for a run to warm up and came back car idling at 1400 rpm. Stopped engine, disconnected MAF. Started engine idle dipped like it was going to die but then settled at between 700 and 750 rpm and it’s a bit “lumpy”. When engine rev’d it dips like its going to stall and then returns to 700/750 rpm. I went for a drive and it didn’t drive too bad – perhaps a little hesitant on acceleration but not massively different.

So with MAF connected it definitely made a difference to idle speed in that it brought it closer to what you’d expect so the MAF is doing something but can I rule it out?

Throttle Position Sensor (TPS)

Read up a bit on this and located it at front of engine

full size click
https://i.postimg.cc/FRqb5XNJ/TPS.jpg


I measured the resistance between the center and outer pins with closed and full throttle
Center pin to righthand pin closed throttle 1320 ohms rising steadily to 4050 ohms at full throttle
Center pin to lefthand pin closed throttle 4410 ohms decreasing steadily to 1700 ohms at full throttle.
I think this is ok??

Another thing on ICV that I read was that when removed if you connect the electrical plug and turn ignition on it shoud vibrate in your hand. I'm too late as it's now in accessible again but I did manage to squeeze a finger on top of it with ignition on and could feel nothing - what do you think / does anyone have any definitive electrical tests that I can do??

Any and all advice greatly appreciated.
 

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