M20 325i low idle @600rpm

Post Wed Jun 11, 2014 12:25 am

Looking for someone to shed some light on a low idle issue I currently have with the 325i cab that I recently bought.

The car currently idles at around 600rpm and the idle is a bit lumpy at times due to this low idle speed.

I read on here that one of the checks which can be done to check for any air leak issues is to remove the oil filler cap whilst the engine is running.

With the engine warm, I popped the hood and removed the oil filler cap and the car cut out momentarily after removing the oil filler cap.

What does this mean? Does this rule out an air leak?
How can I find the culprit and fix this idle issue, and what are the next checks I should carry out?

Thanks

Post Wed Jun 11, 2014 7:53 am

It should be around 600 at idle, If it is a little lumpy it could be as simple as spark plugs need a clean or change. Basics first then look further.

Post Wed Jun 11, 2014 8:50 am

zaust wrote:It should be around 600 at idle, If it is a little lumpy it could be as simple as spark plugs need a clean or change. Basics first then look further.

I've been told on another post that it should idle at around 850rpm

Regarding it cutting out when removing the oil filler cap whilst running, what can that be?

Post Wed Jun 11, 2014 10:32 am

http://www.e30zone.net/e30zonewiki/index.php/Intake

Post Thu Jun 12, 2014 6:24 pm

zaust wrote:It should be around 600 at idle, If it is a little lumpy it could be as simple as spark plugs need a clean or change. Basics first then look further.

You sure about the 600 Marc, always had mine around 850 and
have all been spot on.

Post Thu Jun 12, 2014 8:36 pm

All of mine sat between 6 and 7k and sweet as a nut.

4 cylinder then yes 8k

Post Fri Jun 13, 2014 1:09 am

UPDATE!!

Cleaned the ICV out with carb cleaner and put it back on a fired the car up and it still idles poor, just as before at about 600rpm!

The rubber intake boot also seems fine and I didn;t discover any cracks in it or anything after carefully examining it.

What I did notice though is that the pipe coming out of the ICV which goes towards the end of the throttle body was very loose in terms of connecting to the throttle body. It easily came out without any pulling as the splines on the metal pipr are worn out.

Could this be causing as issue, as in can this being loose affect the idle, even though it's position after the ICV?

What shall I check/Clean next?

Thanks

Post Fri Jun 13, 2014 9:00 am

Possibly. You could try sealing it up using PTFE tape or silicone sealant. Try cleaning out the throttle body and TPS with carb/brake cleaner, and ensure it is set up correctly.

Post Fri Jun 13, 2014 9:11 am

Speedtouch wrote:Possibly. You could try sealing it up using PTFE tape or silicone sealant. Try cleaning out the throttle body and TPS with carb/brake cleaner, and ensure it is set up correctly.

Is there a good guide anywhere on the internet on how to remove and clean the throttle body and TPS?

Also, I have no idea how to check the TPS is set up correctly, so a guide would be excellent. It does click when the throttle is applied slightly. Does this means it's correctly set up?

Would you recommend cleaning the AFM with carb cleaner too? I took off the boot and the nasty K&N filter fitted to the car, and theres a little bit of oil around the exit of the AFM, is this meant to be there or is the AFM meant to be clean and oil free for proper operation? The flaps have some slight resistance and tick once when opened, just the the TPS ticks once, when the throttle is applied, is this correct?

Thanks

Post Fri Jun 13, 2014 9:20 am

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

Yes, you could use carb/brake cleaner to clean the AFM. It shouldn't have any oil in it! This may indicate that the piston rings and/or valve guides are worn, allowing oil to be blown back into it - I would run a compression check, to ensure all six cylinders are giving around 170-190psi.

Post Fri Jun 13, 2014 9:34 am

Speedtouch wrote:http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

Yes, you could use carb/brake cleaner to clean the AFM. It shouldn't have any oil in it! This may indicate that the piston rings and/or valve guides are worn, allowing oil to be blown back into it - I would run a compression check, to ensure all six cylinders are giving around 170-190psi.

I wouldn't say it's got oil in it actually, it just looks like it has a golden glazing on it, most probably dirt. Looked dirty, but dry to the touch.

Engine has been rebuilt last lear by JustE30z, and has covered 400 miles since, but the car has been stood for the majority of the time since the engine rebuild.

It's got very noisy tappets too, so I'm guessing that adjusting those will also give me a slight improvement right? Also, binning the K&N Filter for the original panel filter may also help I guess?

Thanks

Post Fri Jun 13, 2014 9:49 am

Sounds like varnish from stale petrol - probably nothing to worry about.

Yes, adjusting the tappets may well make a significant differnece to the idle speed, changing the air filter less so, unless it is badly clogged with dirt.

Post Fri Jun 13, 2014 10:02 am

The things to do on my list, one by one, to try and find the culprit are the following:

1) Full service [plugs, oils, filters]
2) Adjust valve tappets
3) Clean throttle body
3) Clean and check TPS switch
4) Clean and test the AFM
5) Seal (or replace) ICV exit pipe to throttle body

ICV has already been cleaned so that's one thing ticked off the list

I'm guessing that after going through and carrying out the above, that "should" hopefully cure the rough idle!

Anything else which people suggest to check/do to help cure this idle issue?