Temporary Rough Idle on Cold Start

[Amos830]

Hello gentlemen,

I am calling upon your collective wisdom once again to solve this dubious mystery.

Upon a cold start my 1984 533i will start, yet have a very rough idle. So rough it could be described as though the car is barely clinging to live whilst emitting a foreboding death gurgle.

This rough idle "stumbling" lasts approximately 8 seconds before the idle returns to normal and the car runs as it should.

Once running there are no perceived issues and while I'm out and about during the day the car starts as it should.

Either searchy failed me in this en devour or my skills as a super sleuth are lacking.

Any ideas?

[Mike W.]

What's it smell like? Super rich? If so you could have injectors leaking down. Could even be a leaky cold start valve slow to seal. Actually when I had leaky injectors it was more like 20 or 30 seconds, but not running as bad as you describe. It seemed to have more to do with how long it sat rather than how cold it was. But that's the direction I'd look.

[Amos830]

I wouldn't say it smells super rich, maybe a little. However it doesn't keep fuel pressure over night. Sounds like maybe she is just loaded up and needs to clear out.

I've attached a video of a cold start up below.

I should have also added that in the last 5000km's I've done the following.

- New cold start valve *pita to change with the intake on
- New idle temp sensor
- New idle control valve *ohms to spec
- New Coil *ohms to spec
- Checked cap and rotor *no moisture, no cracks, ohms to spec
- Checked plugs *all burning clean
- Cleaned and re-calibrated the air flow meter *adjusted the track
- Changed oil *Mobil 1 15W50
- New O2 sensor
- Installed new exhaust *SuperSprint and replaced manifold gaskets* no leaks
- Checked throttle position sensor *adjusted properly
- Cleaned throttle body * throttle cable adjusted properly
- Cold compression check - all within 10%
- New fuel pressure regulator *Installed in-line fuel pressure gauge - regulator functioning properly - no fuel leaking to vacuum line
- Rebuilt injectors *but not tested -home rebuild and clean
- New vacuum lines and bellows boot

I'm not normally this proactive all in one shot but I wanted to get the car ready for a couple thousand km family vacation.. which was great! Other than the cold starts.

I was thinking perhaps whatever controlled the air/fuel mixture before the O2 sensor kicked in was failing or some other new component is kaput.



Cold Start Video

[alabbasi]

It does sound like a fuel pressure issue. Either fuel is leaking of the rails through the injectors or back into the tank. Assuming that it also takes a few cranks to get it going?

[Fedaykin528e]

Please excuse if this is a supernoob useless response, but did you try cleaning the plug connection to the ICV and cold start sensors? I have had rough initial idle issues in the past that have been solved in seconds with a can of QD electrical contact cleaner.

If this does nothing, then listen to these guys! ↑

[Mike W.]

I was thinking perhaps whatever controlled the air/fuel mixture before the O2 sensor kicked in was failing or some other new component is kaput.

That would be the AFM, which even after the O2 sensor starts working still provides the single largest input for fuel delivery.

[Amos830]

Thanks so much for the input!

I'll look into testing the AFM and checking the injectors.

[Amos830]

Update:

I haven't had much time to tinker with it due to the work schedule.

However I started her up this morning with the usual results, slight hesitation, and I let it warm up.

I then decided to test for vacuum leaks by removing the dipstick and the valve cover cap. While it's still cold it kills the engine BUT once it's warm, removing these two causes no rpm change.

What I find odd is that with both the dipstick out and the valve cover cap off she idles rock solid at 750rpm and still rev's smoothly without any hesitation!

If I remove the breather tube and/or the icv tube from the intake bellows and try to rev it at all she dies, however it will idle at a solid 750rpm with both these out as well.

If I pull a FPR vacuum line off from the bottom of the intake the rpm does seem to change slightly, but this might just be in my head.

I have an acquaintance with a smoker machine so I guess I'll be doing that on my day off however until then I'm curious as to what is actually happening with the car to make it run so well with such a harsh vacuum leak.

Does that mean the CTS, AFM and ICV are all compensating for the vacuum leak or is something potentially more sinister happening?

*On a different point: with the potential of the injectors sticking ON TOP OF EVERYTHING ELSE, I'm nervous fuel may have leaked into the crank case. Oil consistency seems normal, via sight (no bubbles) touch and smell but cylinder wash is a horrid thought to me.

[tn535i]

Pulling the FPR line adds fuel with slightly increased rail pressure. If you do that is the cold start up better? You could also unplug the O2 sensor and see if that changes anything? These would give a clue.

But start by fixing any vacuum leaks which cause all sorts of problems (especially at idle with low air flow) and you need to do that first or you are just going to be compensating for something outside what the whole system is intended to work within. It could be that simple and it just has difficulty with it's inital adjustments to keep running.

Now at this point I'm not so clear on your model if it is like a later car? If it is then checking the idle control system making sure the TPS and ICV are working properly and after all the above maybe make adjustments to the AFM bypass based on the O2 sensor voltage to get it to idle as it should when it is fully warm. For example a solid idle with NO fluctuations might indicate a too rich or too lean condition. It really should dither back and forth from rich to lean when warm, about every 3-5 seconds.

Some cars will idle OK at the minimum fueling commanded by the ECM meaning you can even unplug the AFM and it continues to idle. I bet you can. Honestly I think that's what it sounds like. You have enough air leaking in that the AFM is basically shut and the ECM is commanding the minimum fuel based on the AFM being essentially at it's lowest value (closed).

[Amos830]

HI tn535i,

The car is a 1984 533i running a b34 on m1.0 basic.

The ICV is brand new and ohms to spec according to the Bently manual.

With reguards to the FPR vacuum line I meant that the car responds differently to vacuum leaks before it fully warms up, ie cold according to the CTS, thermostat, etc.

With reguards to the AFM, if I disconnect the AFM the car stalls.

[Amos830]

Got a chance to work on the car yesterday.

Ripped apart all the vacuum lines, tested and replaced. I'm confident that if there are vacuum leaks they're not obvious!

I also dismantled the injectors, tested them and found two that had a VERY slow leak.

I replaced the injectors with known good ones and re-tested. No injector leaks!

I also took apart the throttle body, cleaned it and re-checked adjustment.

Still having slight hesitation when the car initially starts and is running open loop. No injector leaks/CSV leaks, a good injector spray pattern, new coil, good cap and rotor and good plugs indicates to me that the stumbling is more of an air issue than a fuel issue.

Tomorrow I'll be testing the AFM and possibly tuning the spring/mixture screw. I have access to another stock AFM if I botch it horribly.

[garageboy]

However I started her up this morning with the usual results, slight hesitation, and I let it warm up.

What does "let it warm up" mean, specifically?

Do you normally do this?

If the answer is yes, don't do this. You warm up a car with einspritzen by driving it at moderate engine speeds.

Not saying this is your problem, but do tell if you observe a difference. Hope this helps.

[Amos830]

Let it warm up:

Starting it and letting it idle until the high-idle rpm drops. Which is usually 20-30 seconds.

I always do this.

I then do not exceed 3000rpm until a while after coolant normal operating temperature is reached, so as to allow the oil to reach normal operating temps.

What happens next is just between me and her.

[garageboy]

Just drive it. If you don't believe me, look in your car's owner's manual. Let us know if you observe a difference.

[Amos830]

Just drive it. If you don't believe me, look in your car's owner's manual.

Which page? Are you thinking about the economy section?

What do you think I'll be helping by "just driving" it? Other than the environment.

Do you think letting it idle for 20-30seconds; often less, on a cold start (1 maybe 2x a day) and allowing the cold thick oil to circulate around is harming it?

Do you think pushing cold air through the radiator will heat up the car faster?

I can let you know right now what difference I'll observe. It'll run like shit for about 8 seconds.

A problem I'm currently trying to resolve.

[Amos830]

Didn't get a chance to play with the AFM today as I figured I should double check that everything else is good before I do.

I checked the O2 sensor and it fluctuates between .2 with the oil valve cap off and .8 at idle after a good drive to get it warm. 0.8 at idle seems a tad high to me. Opinions?

I also tee'd in a vacuum gauge and she's a solid 16in at idle. Is this good / acceptable?

Finally I re-checked the CTS and it's testing within spec.

[Acid House]

My car is having a similar issue out of nowhere.

I am associating it with the cold weather, because as you say it starts normally when its been driven that day or even on warmer days.

I am going to have a buddy crank it over when it's cold tomorrow and have a look, for some reason I feel like one of the belts is shrinking/expanding and doesn't fit properly when cold?

It's running great in every other way after the coughing spurt but man oh man what an awful noise

Edit: seems different than yours after watching the vid, I will have a look at it tomorrow.

[garageboy]

Just drive it. If you don't believe me, look in your car's owner's manual.

Which page? Are you thinking about the economy section?

No, dude, read the friendly manual. Page 40 to 43, specifically page 43.
http://www.slideshare.net/BahadirALTUN/ ... k-13406646

What do you think I'll be helping by "just driving" it? Other than the environment.

Do you think letting it idle for 20-30seconds; often less, on a cold start (1 maybe 2x a day) and allowing the cold thick oil to circulate around is harming it?

Do you think pushing cold air through the radiator will heat up the car faster?

I can let you know right now what difference I'll observe. It'll run like shit for about 8 seconds.

A problem I'm currently trying to resolve.

OK, smart guy. Make fun of what you don't understand. First, try reading the manual and what the manufacturer (not me) tells you. Then, I'm happy to discuss.

One question: Do you still have the old cold start valve? Not sure where you got the new one, but I would put the old one back in as a test, pain in the ass or not.

Another question: How does one "check" a cap and rotor? These are maintenance items. Unless you can tell me how many miles are on them and how long they've been on the car, they're definitely still suspect.

And having watched this video, when it's "fine", it was idling at 1000 rpm. Is that "normal"? That is not normal.

It seems to me that your belief that throwing parts at a problem that wasn't necessarily a problem just prior to your vacation has changed so many variables at once that until you can confidently remove variables from the equation (which requires you to assume new parts are also potential problems) this issue may go on for awhile. Good luck.

[Amos830]

OK, smart guy. Make fun of what you don't understand. First, try reading the manual and what the manufacturer (not me) tells you. Then, I'm happy to discuss.

I read my manual today. The only mention of not letting the car warm up (I could find) is in the section dedicated to economy. A practice I fully agree with, with regards to economy. However, when it comes to engine longevity I disagree with the zero warm up time course of action and never read anything that would convince me 20-30s of idling on a stone cold engine will harm it. Most of what I've read on the subject affirms this opinion. http://porsche356registry.org/resources ... dures.html

One question: Do you still have the old cold start valve? Not sure where you got the new one, but I would put the old one back in as a test, pain in the ass or not.

Bav auto I think, maybe BMA. I also removed the ICV inlet tube to the bottom of the intake manifold and watched the spray pattern and put 40lbs of pressure of fuel to it to see if it leaked. It did not. ie, The csv test as described in the Bentley at 7:24-25. I just kept the valve in the manifold. I did this before an oil change, just in case you're worried about the oil.

Another question: I don't know how to "check" a cap and rotor. These are maintenance items. Unless you can tell me how many miles are on them and how long they've been on the car, they're definitely still suspect.

You check them with a volt/ohm meter and visually for wear as described in Bentley 8:6-7. They have 8672km's on them, approx 5388 miles. Installed 642 days ago. lol Ya gotta love maintenace logs and internet calculators.

And having watched this video, when it's "fine", it was idling at 1000 rpm. Is that "normal"? That is not normal.

Yep, she idles at roughly 1000rpm for 10-30s when she's cold. Then it drops to 750rpm with a very slight dither. I thought that was normal. :S

It seems to me that your belief that throwing parts at a problem that wasn't necessarily a problem just prior to your vacation has changed so many variables at once that until you can confidently remove variables from the equation (which requires you to assume new parts are also potential problems) this issue may go on for awhile.

The parts that I changed were parts that were due for change ie, not in spec or had an unknown history. My 528e and my 533i share many similar parts so some of the parts were new parts I bought for the 528e that I simply transplanted for diagnostic purposes, ie the ICV, coil.

Good luck.

Thanks man. I know sincerity and friendly sarcasm aren't conveyed all that properly via the interweb and my tone can be misinterpreted but I am genuinely grateful for your input.

[bane.oh]

Cheers Amos830 for dealing with the grumpy troll. Expertly played.

[wkohler]

The 1000 rpm idle until warm is normal. The switch in the thermostat housing closest to the fan monitors the coolant temp. Once the temp reaches the desired point, the circuit closes and the idle drops to 750 (in theory).

I personally would lean towards replacing the coolant temperature sensor (white insulator nearest the head), especially if you don't know when it was last replaced. It's inexpensive and could be a likely cause of this issue. There's a resistance spec in the Bentley for it. You could test it first.

[tn535i]

Didn't get a chance to play with the AFM today as I figured I should double check that everything else is good before I do.

I checked the O2 sensor and it fluctuates between .2 with the oil valve cap off and .8 at idle after a good drive to get it warm. 0.8 at idle seems a tad high to me. Opinions?

I also tee'd in a vacuum gauge and she's a solid 16in at idle. Is this good / acceptable?

Finally I re-checked the CTS and it's testing within spec.

The O2 sensor voltage should really dither between about .2 and .8 volts about every few seconds once it is warm. Usually I would say adjust the bypass screw on the AFM to get the mixture dialed in so that it does at idle. Your are rich (0.8v) at idle which would suggest open the bypass screw. However, you shouldn't adjust that screw untill you have any vacuum leaks sorted out. Removing the oil cap (leak) drove it lean (0.2v). It really should about die with the oil cap off so if it still runs I'm guessing the AFM bypass screw is mostly closed and you are ricj even if you have a vacuum leak. Just a guess though. Maybe no leaks and just way to rich on the AFM base idle setting.

Next step would be to run it up about 1500 rpm and see what the O2 sensor does at this point. If it does bounce hi-low-hi-low... then you know the O2 sensor and ECM are controlling properly. Once you think any leaks are fixed now you need to get it to do the same on a warm idle condition adjusting the AFM bypass or spring. Don't go casually adjusting the spring. Normally you only adjust the spring if the mixture is way off at the higher rpm range. I would only do it if able to monitor the O2 sensor under throttle and load. Ideally when it goes open loop the AFM is running you just slightly rich.

I think 16 is maybe a bit low. I think a healthy motor at idle should be closer to 20. I would need to check. Of course individual gauges acuracy varies about like the weather. But with a vacuum leak it will be a little low. BMW puts the whole block under vacuum which is a good thing in many ways but makes leaks a big deal.

Somewhere in this process when you get the idle to settle properly warm I would then consider making a fine tune of the throttle base position. Opinions varies but I suggest you simply unplug the TPS once warm. The ICV will go to 'home' and the idle may either speed up or slow a little. I like to adjust the base throttle so that it runs a couple hundred rpm faster with no load on a warm engine. That puts the ICV in the sweet spot for it's control range and minimizes any on-off idle transitions. Of course every time you make an adjustment you need to then check and re-adjust the TPS.

Keep going you'll get it...

And I will often let my car warm up a bit (even a few minutes) before driving off and sometimes just drive off. If cold it should start and idle just fine and if cold enough (near freezing) that's above about 1200 rpm. Never any higher revs or full loads till the engine warms out of the blue is my rule. What you described sounds just fine.

[Amos830]

Well.. it's fixed.

Yesterday I had a couple hours to fiddle with it.

I didn't like that it was only reading 16inHg *measured from the FPR vacuum line, ie intake vacuum* at idle and although the rubber under the hood is still soft and virtually new I figured I'd try a crude test. I took off the bellows and the icv tubes and tightly wrapped them in saran warp *silly I know* and re-installed and re-tested. I picked up an additional 3inHg. There are seriously no cracks in these tubes than I can see. :shrug:

An interesting point is that if I remove the oil fill cap or dipstick an immediate vacuum loss in the intake isn't apparent once the engine is warm. The intake will stay at 19inHg with both the oil cap and the dipstick out for an indeterminate amount of time 3s-30s. Though it seems I can expedite the drop my cracking the throttle. Either way I'm happy with the increased vacuum pressure and am re-ordering all new rubber.

However no apparent changes with the issue.

I also wanted to follow your leads with the AFM but did not want to fiddle with it until I was 110% everything else was in spec. So I pulled up some diy material * http://www.the944.com/afm.htm* and went testing.

http://s346.photobucket.com/user/Amos83 ... 9.jpg.html
http://s346.photobucket.com/user/Amos83 ... f.jpg.html

The potentiometer tested beautifully but it seems the temp sensor is a tad off. That reading was at 23C. I figured I'd do some more testing so I didn't adjust anything.

Once back together I figured I'd take another run at the O2 sensor. After a good drive I tested it again and was having issues getting it to test properly. I re-checked the wire and connections and found that they were good AND I was in a what the hell mood so I grabbed a new O2 sensor from my stock-pile and threw it in. After another drive she's swinging from .2-.8 with very nice dither. To continue with the what the hell spirit I ran new fresh wire. *Single wire O2 on a 535is exhaust so it needs and extension. *Don't worry I plan on doing a 4 wire conversion soon.

Still no apparent changes.

While I was on the second drive I stopped off at the local shop and grabbed a new CTS. What the hell right, it's $20. The old one tests fine but, whatever I'll keep it as a spare.

Snugged it in and no apparent changes.

I grabbed the main relay out of the 528e and popped it into the 533i.

No change.

Finally I thought, what the hell *see the pattern?* and swapped in one of my known good ECU's.

Voila!

She's starting great! And now has the added benefit of a new CTS and an O2 that's reading correctly.

However to sour things I detected a slight vibration in neutral at an rpm of roughly 2000rpm. I pulled off the fan/fan clutch at the belt to the alt/water pump and the vibration all but disappeared. So a new water pump will also be ordered.

I won't have time to fix it and will have to keep driving the car for the next week. The vibration is pretty slight. Here's hoping she holds together.

Thank-you all again for all your help. Your combined efforts help keep these e28's on the road!

[tn535i]

Good work. Get all the potential leaks fixed, then adjust the AFM bypass setting and throttle plate and I bet not only is this issue fixed but it behaves better all around. I guess my logic is that the idle control takes 'longer' than usual to get into control because something is out enough it has to go to an extreme to adjust. It just seems to all work better when it's close to the sweet spot. A leak will drive it farther away to compensate and I think it works best when it just needs to open a little cold and then close a little warm.

[Amos830]

Good work. Get all the potential leaks fixed, then adjust the AFM bypass setting and throttle plate and I bet not only is this issue fixed but it behaves better all around. I guess my logic is that the idle control takes 'longer' than usual to get into control because something is out enough it has to go to an extreme to adjust. It just seems to all work better when it's close to the sweet spot. A leak will drive it farther away to compensate and I think it works best when it just needs to open a little cold and then close a little warm.

I 100% agree and will get that sorted as soon as the parts arrive and the wife lets me out of the house gain.