Rough idle after warm up. Hrmm...

[wagons ho]

Pistons need heat at sustained rpm to loosen carbon from ringlands. Like, running down the road at 80 plus for an hour at a time.
Quick blasts probably put more fuel in cylinder and add to problems.
Also, switching from synthetic to dino oil, and additives like marvel mystery or other type to cut buildup.
I've brought back several mechanically sound but fouled engines this way.

Also, plus 1 to everything RShaffner said. He's much more detailed, I'm quick and to the point.

[R Shaffner]

Waters17:

I was suggesting pinching/blocking the hoses because you were still looking for an intake leak. If you think all the leaks are fixed now, from the computer scans, that's probably not necessary. (Couldn't hurt tho.)

About the roughness test, I read that having the readings under 100 was what we should shoot for. Having relatively even roughness scores, if they are high, would NOT be good. (Even compression numbers yes, even roughness no. We want those low.)

Recently I suspected some of my coil packs were going bad, and I'd saved a few old ones as spares. I used INPA's roughness screen to see which ones had scores over 100. I swapped those coil packs to other cylinders. The differences were not exact, but it was clear that the scores changed and were higher with the suspect ones. I replaced those packs with some old ones and got all the scores under 100. I could tell the difference in how the car drove.

Another thing...

How are the engine mounts? The ones on my '97 went soft around that mileage. One even came apart so that side of the engine could lift up. When you watch it and rev it, does it shift more than normal? Transmission mounts can go bad too. Loose/bad mounts can magnify any roughness in the engine.

And finally...

When you pull the plugs for the compression test, keep track of them, examine them, and compare them to one another. (If you're not sure what different looks mean, compare your plugs to pics online.) If any plugs look different, they might be pointing to another cause of the poor idle, and of course fouled plugs can then cause a poor idle. Plugs can be swapped around too, but they're so cheap I'd just replace any that look suspect.

[waters17]

I was suggesting pinching/blocking the hoses because you were still looking for an intake leak. If you think all the leaks are fixed now, from the computer scans, that's probably not necessary. (Couldn't hurt tho.)

I'm still going to run DIS scans when I get a little bit of time.

Recently I suspected some of my coil packs were going bad, and I'd saved a few old ones as spares. I used INPA's roughness screen to see which ones had scores over 100. I swapped those coil packs to other cylinders. The differences were not exact, but it was clear that the scores changed and were higher with the suspect ones. I replaced those packs with some old ones and got all the scores under 100. I could tell the difference in how the car drove.

I'll swap them around. Chances are if one or two of them are bad, I'll most likely replace all of them.

How are the engine mounts? The ones on my '97 went soft around that mileage. One even came apart so that side of the engine could lift up. When you watch it and rev it, does it shift more than normal? Transmission mounts can go bad too. Loose/bad mounts can magnify any roughness in the engine.

The mounts only have 10k miles on them. I'm confident they're good.

When you pull the plugs for the compression test, keep track of them, examine them, and compare them to one another. (If you're not sure what different looks mean, compare your plugs to pics online.) If any plugs look different, they might be pointing to another cause of the poor idle, and of course fouled plugs can then cause a poor idle. Plugs can be swapped around too, but they're so cheap I'd just replace any that look suspect.

Good idea!

An easy way to test coils (that has worked well for me): Open the throttle wide below 2,000 rpm in 2nd or 3rd (without downshift). Does it stumble or hesitate? If so, that usually tells me one or more coil packs are going bad (though they might work well enough at other times to not throw any codes).

So what do you mean here? I have a manual transmission, so I don't need to worry about downshifting. I tried cruising at 2,000 and 3,000 rpm, but it seemed pretty smooth.

[jicaino]

^he means short shift it, and starting at around 1000 rpm 20ish mph in 3rd floor it. If it gasps ever so slightly before get-going, you could have tired coils which would be my next guess at 150k. and no history of replacement. I swapped my original 16 years old coils a while back and man, OH man, it was like "booom". A big big difference in response and idle smoothness.

[waters17]

Damn, I wish you would have replied before lunch so I could test it out over my break.

[wagons ho]

When you pull your plugs and coils to swap them around,
DO A COMPRESSION TEST!
8 pages of ideas that haven't helped.
In my belief, (which people take issue with) coils do not get weak. They work or fail.
Original coils in my car @ 185k.
Plugs, who knows, they were in there when I bought it.
And waters, you are not experiencing any misfire or backfire, just poor idle, correct.
Take the ohm meter to the coils.


There is one brand of car known for "bad" coils. And they are bad every 20k or so. That car is also known for bad oil leakage in the spark plug well. Which could be causation, but still blamed on coils. That fine car is jaguar and German fords,and tbird that use the same engine. But that's not what we are talking about here.

[waters17]

I will, I will. I didn't have any time to do it yesterday. I'll do it sometime this week and report my findings.

Correct, no misfires or backfires. IIRC, not all my coils are the same. I could be remembering totally wrong though. I'll update later.

[jicaino]

I also sustained the theory that coils either work or not and then I swapped a whole new set of coils. My car is known for running smooth and idle perfectly, it was that way and has been that way since I removed precats when I got it. Now after having swapped all them coils I was amazed at hom much of a difference it made.

[R Shaffner]

Jicaino -- Yes and Yes. Thanks!

[R Shaffner]

Just to be clear, I'll notice the slight hesitation when I floor it at 2,000 rpm in 2nd or 3rd because I do that often enough as I normally drive. (Why downshift when all that sweet torque will pull me up to speed?) If I had an automatic I'd never notice it because it would kick-down, of course. And after I feel the hesitation the engine pulls strong all the way up. So the coils are clearly working well enough for that, with no codes.

But after I find and replace the sub-par coil packs, no hesitation from 2,000 or so when I punch it.

[waters17]

I tried it but I'm not sure what I should be feeling for. Normally when I idle and goose the throttle, I hear a slight whistle of air being drawn in to the motor and then the motor responds. This all happens in about a half second or so. I just assumed it was due to the DBW setup. I experienced the same thing when I tried flooring it at 2000 rpms. I can record audio of it later. When I do this at idle, there are three distinctive sounds that are heard in order. I hope it translates when I record it.

Pedal sound->intake sound->engine sound

I'm guessing the intake sound and the engine sound should be closer together and possibly overlap. It'll make more sense when I upload audio.

[jicaino]

I tried it but I'm not sure what I should be feeling for. Normally when I idle and goose the throttle, I hear a slight whistle of air being drawn in to the motor and then the motor responds. This all happens in about a half second or so. I just assumed it was due to the DBW setup. I experienced the same thing when I tried flooring it at 2000 rpms. I can record audio of it later. When I do this at idle, there are three distinctive sounds that are heard in order. I hope it translates when I record it.

Pedal sound->intake sound->engine sound

I'm guessing the intake sound and the engine sound should be closer together and possibly overlap. It'll make more sense when I upload audio.

That sounds like you're describing lag, the lag that bad coils produce. DBW is actually better in terms of throttle response than cable. Have you replaced thtottle body, accelerator pedal ? coils we know you haven't. These 3 things could all or one of them be causing idle gremlins as well.

- - - Updated - - -

Just to be clear, I'll notice the slight hesitation when I floor it at 2,000 rpm in 2nd or 3rd because I do that often enough as I normally drive. (Why downshift when all that sweet torque will pull me up to speed?) If I had an automatic I'd never notice it because it would kick-down, of course. And after I feel the hesitation the engine pulls strong all the way up. So the coils are clearly working well enough for that, with no codes.

But after I find and replace the sub-par coil packs, no hesitation from 2,000 or so when I punch it.

I have a Dinan stage 3 tranny tune that won't downshift under those parameters and I've ran that EGS for years so I know what you mean. That's the first thing I noticed when replaced the coilpacks. It was like I just remapped the throttle response curve in the pedal.

[waters17]

Pedal is still original. Throttle body was replaced (VDO) 19k miles ago. I'm going to explore the coil issue first. Probably not until this weekend. Ambition is pretty low after work.

[waters17]

Okay, here's the audio clip.

https://soundcloud.com/andy-waters-5...tle-hesitation

[Chedley]

Just a trivial question: did you reset the adaptations after cleaning the throttle and replacing the coils and spark plugs ?? You should.

[jicaino]

Under load, man!
Even so I hear some hint of "fat guy choking on the world largest taco".... is your intake resonator in place? All of the vac and evap lines to the intake elbow are safe and sound? Fuel pump is ok? Fuel filter replacement history? Have you checked your fuel pressure? If.you remove your dipstick things changes?

[jicaino]

Í just had an idea. Check the SAP valve an crossover tube o-rings. That's an exhaust leak after warmed up if the valve is bad, or if the o-rings gave up the ghost.

[waters17]

Just a trivial question: did you reset the adaptations after cleaning the throttle and replacing the coils and spark plugs ?? You should.

Yeah, I pretty much reset adaptations whenever I run INPA.

Under load, man!
Even so I hear some hint of "fat guy choking on the world largest taco".... is your intake resonator in place? All of the vac and evap lines to the intake elbow are safe and sound? Fuel pump is ok? Fuel filter replacement history? Have you checked your fuel pressure? If.you remove your dipstick things changes?

I can try to get you some clear audio under load.
Intake resonator is in place
vac and evap lines are all new and secure
Fuel filter was replaced 9k miles ago

I haven't checked fuel pressure or the pump.
**I'll remove the dipstick later tonight and report my findings. I do recall a suction noise, but I can't say for sure if it upsets the idle.**

Í just had an idea. Check the SAP valve an crossover tube o-rings. That's an exhaust leak after warmed up if the valve is bad, or if the o-rings gave up the ghost.

Those o-rings have about 40k miles on them, but the issue has persisted pretty much that whole time.

The rough idle is noticeable during warm up, but once that secondary pump shuts down, the idle quality will get worse.

[jicaino]

Have you tried block off plates and see what happens?

[waters17]

Have you tried block off plates and see what happens?

I'm going to check the coils first, but for future reference, what's the purpose of block off plates and at what location would I try them?

[jicaino]

They seal the ports of the SAP piping on the face of the cyl heads. That could be a nice exhaust leak there, if for some reason the SAP valve is slurry and doesn't closes all the way. That valve is the old school glass fuel filter looking thingy under the MAF area.

I'd also replace all the coils and spark plugs if tha was my car. You'll hear a lot of junk about how bosh are bads and all. I've been running on Bosch Super Plus plugs for all of my 540i life and I've replaced just 2 sets of them. Never an issue. I even have ultrasonic cleaned the old ones I replaced the last time and they were like new. Get the "Made in Germany". Also use permatex dielectric grease on both sides of the boots, and on the wiring harness plugs, and on the nuts that clamps the coils down.

[waters17]

I swapped coils today and noticed some positive changes, but then I did the compression test and I think that may be where my problems are coming from.

TIS says compression should be 176-206 PSI?
CYL 1: 170 PSI
CYL 2: 175 PSI
CYL 3: 160 PSI
CYL 4: 165 PSI
CYL 5: 180 PSI
CYL 6: 175 PSI
CYL 7: 175 PSI
CYL 8: 160 PSI

I also can't get my car started now. Can't connect to INPA to see anything. "IFH-0003: NO RESPONSE FROM CONTROL UNIT" My guess is the DME needs to be re-aligned. Can't remember how to do that though.

[wagons ho]

You knew that I would check in eventually. The only suprising thing is that the compression numbers don't jive with the cylinders that inpa gave as weak.
So no, coils will not smooth out your engine.
Now, assuming that your cylinder bores are not scored, or that your valves are leaking?
Both can be checked, leakdown check and borescope, but I think we can rule out major problems.
Are you ready to treat your engine for carboned rings?
Non synthetic oil and additives. And forget 6th gear for a while.
Like I said in post #177

[R Shaffner]

GG did a great write-up about getting the computers aligned. Here it is:
https://www.bimmerforums.com/forum/s...ends-are-wrong

With compression tests, I understand that the most important thing is consistency. Some places I've read say that on an old engine having a variation within 10% is considered OK. That fits my experience. In your case the low is 160 and the high is 180, so that variation is a little more than 10%, but not awful.

How did the plugs look when you pulled them? Any fouled or wet plugs? Did any look different than the others?

Also, the point about swapping coil packs is to see if the roughness on INPA stays with the cylinder or follows the changed pack. Unless you have a new pack or two that you're swapping in, of course, in which case the idle and other symptoms might improve if the old coil pack wasn't great.

And, finally, did you try a little bit of oil in the cylinders after the compression test to see is that helped? (If the compression in a cylinder is low because the rings are worn, it will be higher if some oil on top of the rings helps hold air in. But not too much oil, which can displace air and make the compression look artificially high).

[waters17]

You knew that I would check in eventually. The only suprising thing is that the compression numbers don't jive with the cylinders that inpa gave as weak.
So no, coils will not smooth out your engine.
Now, assuming that your cylinder bores are not scored, or that your valves are leaking?
Both can be checked, leakdown check and borescope, but I think we can rule out major problems.
Are you ready to treat your engine for carboned rings?
Non synthetic oil and additives. And forget 6th gear for a while.

Like I said in post #177

Pistons need heat at sustained rpm to loosen carbon from ringlands. Like, running down the road at 80 plus for an hour at a time.
Quick blasts probably put more fuel in cylinder and add to problems.
Also, switching from synthetic to dino oil, and additives like marvel mystery or other type to cut buildup.
I've brought back several mechanically sound but fouled engines this way.

When I get the car to start, I'll try out the non synthetic oil and additives. I have a borescope, and I can try that, but I don't have a leak down tester, so I'll have to put that one off until a later date.

GG did a great write-up about getting the computers aligned. Here it is:
https://www.bimmerforums.com/forum/s...ends-are-wrong

With compression tests, I understand that the most important thing is consistency. Some places I've read say that on an old engine having a variation within 10% is considered OK. That fits my experience. In your case the low is 160 and the high is 180, so that variation is a little more than 10%, but not awful.

How did the plugs look when you pulled them? Any fouled or wet plugs? Did any look different than the others?

Also, the point about swapping coil packs is to see if the roughness on INPA stays with the cylinder or follows the changed pack. Unless you have a new pack or two that you're swapping in, of course, in which case the idle and other symptoms might improve if the old coil pack wasn't great.

And, finally, did you try a little bit of oil in the cylinders after the compression test to see is that helped? (If the compression in a cylinder is low because the rings are worn, it will be higher if some oil on top of the rings helps hold air in. But not too much oil, which can displace air and make the compression look artificially high).

I remember when he posted that. I totally forgot about it though. His write-up has given me some things to check, but it's like I'm not even getting power to the DME. I've started another thread on that topic though.

Plugs looked fine.

Roughness changed on a few cylinders, but some stayed the same. The results were negligible. I left my notes at home, but I can post the actual roughness results later.

I did not do a wet test. I looked into it briefly, but that's about as far as I went.