M20 Rough Idle

[EngPhys09]

I don't know if any one else on this forum has had this issue but I wouldn't mind some opinions.

I have a 90 525i, m20 engine with a 5spd. 145k on the motor. Now that its cold out I've noticed a few things that are very predominate with its colder out.

1. When I pull up to a stop light and push the clutch in the engine will drop to about 700rpm then up to 950rpm and slowly approach a comfortable idle after 10 seconds. Now I was just wondering if this could be sensor related, no warring light are on? Or is it just a fact of temperature.

2. I notice that its also very tough to shift when its colder out until the car warms up. I do have a UUC SSK so this is a bit of the problem. But I wasn't sure if anyone else had similar issues.

My major thought is that it needs a rebuild along with the motor which will happen within the year.

Thanks

[DaveVoorhis]

Neither of these issues sound like justification for an engine/tranny rebuild, unless they're clearly worn out. The former could be a vacuum leak or a dirty Idle Control Valve. The latter suggests need for a tranny oil change, possibly to a synthetic.

[Turbo Ready]

^^^ Very true

[RichG]

Mine has 240k on it. If I disconnect the battery and the computer has to re-learn, it will also drop to 700rpm when I push the clutch in and almost die and then jump to about 950rpm. After maybe 10 times doing this, it learns it can't idle at 700 rpm and just idles at around 900rpm. I have a Dinan chip, so I don't know if it's the programming of the chip or this duplicates the stock chip.
It never has idled well (I have only had it for about 20k miles) and I've changed idle control valves with no change. I've pretty much given up on having it idle well, but it does ok running and after the 10 times learning, it doesn't want to die at lights.

Mine is also hard to shift when first starting to move when cold, so I just take it easy the first couple of minutes and then it's fine.

So you're not the only one with these problems.



I don't know if any one else on this forum has had this issue but I wouldn't mind some opinions.

I have a 90 525i, m20 engine with a 5spd. 145k on the motor. Now that its cold out I've noticed a few things that are very predominate with its colder out.

1. When I pull up to a stop light and push the clutch in the engine will drop to about 700rpm then up to 950rpm and slowly approach a comfortable idle after 10 seconds. Now I was just wondering if this could be sensor related, no warring light are on? Or is it just a fact of temperature.

2. I notice that its also very tough to shift when its colder out until the car warms up. I do have a UUC SSK so this is a bit of the problem. But I wasn't sure if anyone else had similar issues.

My major thought is that it needs a rebuild along with the motor which will happen within the year.

Thanks

[vince]

I have a 1990 525i with an M20 and 5-speed, 190k miles. I've gone through the entire a/f system and replaced a bad a/f meter, but the idle, especially when cold, initially hunts around a bit.

I am using Redline MTL in the trans, and it shifts much better than when it had regular geal oil. Shift mech is stock, though, and I've had ss kits that were notchy in some cars.

Hope this helps,

vince

[EngPhys09]

Neither of these issues sound like justification for an engine/tranny rebuild, unless they're clearly worn out. The former could be a vacuum leak or a dirty Idle Control Valve. The latter suggests need for a tranny oil change, possibly to a synthetic.


Well i plan on rebuilding the engine because I have bad compression in 2 cylinders, wet compression is good. And i figure if I'm pulling the engine out i might as well fix the trans.

Thanks for the opinions on oil for the tranny. I'll take a look around the engine for a leak but I think its just the cold weather. I'm running a 20W50 oil just because of some leaking issues, another reason to rebuild the engine.