Rough idle - how smooth should it be?

[BristolE30]

Hey zone

I’ve noticed my 325i doesn’t idle super smoothly. It’s fairly constant but it feels like it is doing mini cut outs, then being saved from stalling. It idles around 600rpm when warm by looking at gauge. Then it might drop to 550 for half a second then back up to 600rpm.

Is this normal for an old car or should it stay perfectly at 800 or something? I cleaned the ICV with carb cleaner but didn’t seem to do much. Seen lots of threads on high idle but what about low idle?

Any help appreciated

[Contours]

I think 750 rpm is the ideal.

[BristolE30]

I think 750 rpm is the ideal.

Yea that's what I'd like to have. Was thinking about just tightening up the throttle cable a bit?

Cheers,

[tha881]

Be careful when adjusting the throttle cable, if you take out too much slack you could activate the tps taking it out of idle mode and into part throttle, not ideal. There is no relation of throttle cable and idle speed. The purpose of throttle cable adjustment is basically to remove slack at the pedal.

[Steve]

Doing that will just hide the real issue, have you check all the vacuum hoses?

[steve_k]

check all the vacuum hoses for any splits no matter how small,

check the gaskets round the inlet side as they could be split which also causes a vacuum leak,

once thats all done post up your findings & someone should be able to help you.

[steve_k]

as steve & tha881 have said don't mess with the throttle cable as that then causes you another issue to deal with.

if you do with to "tack the slack out of the throttle cable" then only do it a fraction,

[Brianmoooore]

Be careful when adjusting the throttle cable, if you take out too much slack you could activate the tps taking it out of idle mode and into part throttle, not ideal. There is no relation of throttle cable and idle speed. The purpose of throttle cable adjustment is basically to remove slack at the pedal.

Exactly this!

[Brianmoooore]

check all the vacuum hoses for any splits no matter how small,

check the gaskets round the inlet side as they could be split which also causes a vacuum leak,

once thats all done post up your findings & someone should be able to help you.

And this! There also should be a blanked off (with a rubber cap) port under the throttle body (assuming you don't have emissions stuff fitted) , almost touching the TPS. This cap deteriorates over time, and often falls off.

[BristolE30]

Thanks for the responses guys. Won’t all of these vacuum leaks cause increased air, thus higher idle?

My idle is wanting to drop out and is rather bumbly and rough. Or can leaks cause a lower idle?

[BristolE30]

Either way I will give the hoses a once over!!

[Brianmoooore]

The leaks will weaken the fuel mixture and cause hunting, which I think is what you are trying to describe as 'bumbly and rough'.
Air that causes a higher idle leaks in downwind of the throttle butterfly. This is air that leaks in after the AFM.

[BristolE30]

The leaks will weaken the fuel mixture and cause hunting, which I think is what you are trying to describe as 'bumbly and rough'.
Air that causes a higher idle leaks in downwind of the throttle butterfly. This is air that leaks in after the AFM.

Thanks mate, having a look over the car but I’m not really sure what I’m looking at/for

[BristolE30]

All the pipes seemed to be intact. There is some sort of oil leak as the TPS was covered in fresh oil.. maybe a gasket is gone?

The cap seemed to be on the port tho. My idle isn’t erratic and you can’t actually see the hunting on the needle - you can just feel it in the seat

[Brianmoooore]

If the weak mixture isn't being caused by air leaks, then the other usual cause is injectors long overdue for a rebuild.

[BristolE30]

If the weak mixture isn't being caused by air leaks, then the other usual cause is injectors long overdue for a rebuild.

That’s probably the case to be honest. If I buy one of those Bosch sets on Ebay, how easy/hard are injectors to remove and replace?

Thanks

[Brianmoooore]

Injector rebuilding is a job best left to the professionals - they have the measuring equipment and test rig required. See the first post in our traders' forum.
Injectors are held in place by the fuel rail and the electrical connector assembly. Remove those and they just pull out.
Flip all the metal springs completely off of the plugs with a small screwdriver to get the electrics off. Refit the springs before refitting.

[BristolE30]

Injector rebuilding is a job best left to the professionals - they have the measuring equipment and test rig required. See the first post in our traders' forum.
Injectors are held in place by the fuel rail and the electrical connector assembly. Remove those and they just pull out.
Flip all the metal springs completely off of the plugs with a small screwdriver to get the electrics off. Refit the springs before refitting.

Do you know the OEM number for our injectors? Considering just buying a whole new set of 6 as they seem to be cheap. Autodoc is offering me these ones, but I feel like they look slightly different to my currents 325i ones? Or is it just a different colour?

https://www.autodoc.co.uk/bosch/1150409

Any help appreciated, just want to find the correct stock ones.

Cheers

[Brianmoooore]

The BMW part numbers in that ad. are the correct ones for what should be on your car.

[Foe]

If the weak mixture isn't being caused by air leaks, then the other usual cause is injectors long overdue for a rebuild.

That’s probably the case to be honest. If I buy one of those Bosch sets on Ebay, how easy/hard are injectors to remove and replace?

Thanks

There's a guy on here, and also a web site, called injector clean. I'm going to get mine done. There's also still a discount for zone members. It will work out a lot cheaper than buying new ones, and at least you know the current ones fit!
Link here
http://www.injectortune.co.uk/Injector_Cleaning.html

Drop him an email, worth a shout.

[Bonymaenjack]

Injector rebuilding is a job best left to the professionals - they have the measuring equipment and test rig required. See the first post in our traders' forum.
Injectors are held in place by the fuel rail and the electrical connector assembly. Remove those and they just pull out.
Flip all the metal springs completely off of the plugs with a small screwdriver to get the electrics off. Refit the springs before refitting.

Do you know the OEM number for our injectors? Considering just buying a whole new set of 6 as they seem to be cheap. Autodoc is offering me these ones, but I feel like they look slightly different to my currents 325i ones? Or is it just a different colour?

https://www.autodoc.co.uk/bosch/1150409

Any help appreciated, just want to find the correct stock ones.

Cheers

Just to say that I recently bought a set from AutoDoc and the transformation was very noticeable, easier to start and better consumption

[BristolE30]

Injector rebuilding is a job best left to the professionals - they have the measuring equipment and test rig required. See the first post in our traders' forum.
Injectors are held in place by the fuel rail and the electrical connector assembly. Remove those and they just pull out.
Flip all the metal springs completely off of the plugs with a small screwdriver to get the electrics off. Refit the springs before refitting.

Do you know the OEM number for our injectors? Considering just buying a whole new set of 6 as they seem to be cheap. Autodoc is offering me these ones, but I feel like they look slightly different to my currents 325i ones? Or is it just a different colour?

https://www.autodoc.co.uk/bosch/1150409

Any help appreciated, just want to find the correct stock ones.

Cheers

Just to say that I recently bought a set from AutoDoc and the transformation was very noticeable, easier to start and better consumption

Good to hear. Did you buy the same ones I put a link for? They fit alright?

Did you remove intake manifold to replace or just unclip them from under it?

Cheers
Jo

[Bonymaenjack]

Do you know the OEM number for our injectors? Considering just buying a whole new set of 6 as they seem to be cheap. Autodoc is offering me these ones, but I feel like they look slightly different to my currents 325i ones? Or is it just a different colour?

https://www.autodoc.co.uk/bosch/1150409

Any help appreciated, just want to find the correct stock ones.

Cheers

Just to say that I recently bought a set from AutoDoc and the transformation was very noticeable, easier to start and better consumption

Good to hear. Did you buy the same ones I put a link for? They fit alright?

Did you remove intake manifold to replace or just unclip them from under it?

Cheers
Jo

Hi yes they're the same but to confirm mine were for a 2.5 . To replace is pretty straight forward with no requirement to remove the manifold although I would suggest removing the rocker cover just to provide a bit more clearance and make sure before you do try and clean the area around where the injectors fit . If you follow the wiki guide https://www.e30zone.net/e30wiki/index.p ... _injectors then its not a dauting task by anymeans.

[BristolE30]

Hey guys,

Little update on this one. Did a valve adjustment today - some had zero clearance some were loose. Changed them all to 0.25. Wow perfect idle. It’s never run so smooth.

Worth a shout if anyone is having a bumbly idle, that isn’t super erratic just annoying.

Very happy

[BristolE30]

[Brianmoooore]

NOT a good idea to park those nuts there! Oil drain holes in the head are big enough for a small nut to go down. (I know from experience.)

[BristolE30]

NOT a good idea to park those nuts there! Oil drain holes in the head are big enough for a small nut to go down. (I know from experience.)

It’s okay I was careful lol. Will remember for next time

[BristolE30]

Bit of an update on this one - I’ve done my valves twice now as I wasn’t 100% sure. Second time I used the special tool and the clearances are perfect.

Still got a rough idle as can be soon in the video. It’s really when it gets warm. It’s very low and goes up and down.

Can’t see any vac leaks at all. Any one else have a suggestions?

I was thinking coolant temp sensor next, then 02 sensor?

[boiliebasher]

If yours it an 88' model, I doubt it's got a lambda sensor to be honest

[boiliebasher]

Blue coolant sensor definitely worth a go however. I bought a genuine bosch one from fleabay a couple months ago for like £12 so definitely worth it imho

[BristolE30]

https://streamable.com/1mxm6 - Shows the up and down

https://streamable.com/s2vjq - Shows it wanting to die every time it comes down on the revs

[Brianmoooore]

Pull off the small rubber hose from the inlet manifold to the fuel pressure regulator at the regulator end. Leave the stub into the regulator open, but block the end of the hose.
Does the engine idle better?

[BristolE30]

Pull off the small rubber hose from the inlet manifold to the fuel pressure regulator at the regulator end. Leave the stub into the regulator open, but block the end of the hose.
Does the engine idle better?

Just tried it but it didn’t really effect it - seemed just as bad :/

[BristolE30]

Just went out and tested the blue coolant temp sensor and it seems to be in spec (2800ohms at room temp) so I guess it’s not.

Really scratching my head now. I’ve noticed the AFM has been dismantled at some point in its life and the cap is missing from the adjustment screw, so some PO has probably had issues. Do think it’s worth me ever so slightly tinkering with the adjustment screw when it’s warm to see if smooths idle out? I know I don’t have all the equipment to measure emissions but figure if it makes it worse I’ll just adjust it back..

Appreciate any thoughts

[Brianmoooore]

Pull off the small rubber hose from the inlet manifold to the fuel pressure regulator at the regulator end. Leave the stub into the regulator open, but block the end of the hose.
Does the engine idle better?

Just tried it but it didn’t really effect it - seemed just as bad :/

This will have made the idle mixture a little richer
I once bought a very cheap two door E30 with a hesitation under acceleration when partly warmed up that noone could fix. Already fitted with a new blue sensor, but a genuine second hand one from a scrap engine was all it needed to get it running properly.
Not only needs to be right at the ends of the range, but at every temp inbetween. Red