Help trouble shooting rough idle and misfire

**thrawn5499** · 02-20-2017, 11:58 AM

So last December the water pump went out on my 1996 740il. While I was replacing it I decided to change some hoses fix valve cover gaskets and put new could and injectors in it. I have been getting a rough idle when it is cold out for a couple of years it has gotten worse to the point when it is cold out side the car won't idle without pulsing the gas pedal. Once the car warms up it would idle smooth. My plugs were fouled so I replaced them while I was doing the rest of the stuff.
About a week before the water pump went out I started getting a misfire on #8 maybe another too can't remember now. I figured it was the plugs do the leaking valve covers. They had oil all around the plugs. I was excepting the car to run almost like new after I replaced all of those parts. It instead runs exactly the same. Rough idle and misfire until you get it to about 3k Rpms then it smooths out and runs fine. Same when you drive it. When it gets to 3k it gets all power back and runs strong. I am going to try hooking it up to the laptop here shortly if I can keep it running I will see what inpa tells me. I am just looking for a few things to check out. I have read could be a vacuum leak though I thought they got worse with more rpms. Bad maf? Doesn't seem like cats to me but maybe I am wrong. It really seems like a plug or coil problem but they should be good. I did pull #8 out and look to see if it was founded again but it was clean. Thanks for the help

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**thrawn5499** · 02-20-2017, 12:22 PM

Ok I hooked it up and scanned with inpa. Not sure which things I should select to scan but I went through a lot and found a few errors.

I then started the engine it did idle though still have a misfire. It is warm out side so that's probably why it will idle now. I took lots of photos but of course the laptop screen is reflective so they all have a bad reflection and I will have to retake most of them.

Here is one for the engine smoothness readout in inpa

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**thrawn5499** · 02-20-2017, 12:57 PM

Here is my log from pa soft.
DME -> Shadow-memory:
8B/44 - Output thermostat

EWS -> FF/3F - General reset

ABS -> 43/FE - Electromagnetic field susceptibility

SRS -> 13/84 - Fault lamp
11/20 - Supply voltage

LCM -> 16/21 - Wire, HVAC (LRA) potentiometer, open circuit
18/01 - Connection to trailer module is disturbed
28/02 - Thermal oil-level sensor defect
Shadow-memory:
53/01 - Engine oil pressure
5F/03 - Check coolant level

ZKE -> 04/21 - Terminal R wire on the GM III
Shadow-memory:
93/23 - Power up from the GM III

MID -> 03/21 - No valid status response of TELEPHONE

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**thrawn5499** · 02-20-2017, 01:03 PM

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**thrawn5499** · 02-20-2017, 01:40 PM

Not sure but looking at the smoothness pic again it looks like most of the problem is located on the passenger side 1-4 I am going to pull those plugs out again and have a look.

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**thrawn5499** · 02-20-2017, 03:57 PM

Ok so I took out #1 plug and cleaned it. It did not look bad but was a little black. Dry not wet. I put it back in and it did t really seem to make a difference. I shut off the car and disconnected #1 coil. Started the car. It didn't seem to make much of a difference in the way it was running. I then hooked one of my old coils up. I did not know if they are good or going bad. I just figured they could be changed since the were still the original one. When I started the car it did seem like it was idling smoother. I checked with the smoothness test in inpa. (Not sure what this is telling me)

big change in #1 with the cleaned plug and old coil. Not sure if this is worse or better but it is a noticeable change in the numbers. Since it seems to be further out of range, I would think this would be worse, but it did seem to be running a little better, though I could be wrong about that.

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**SergeBMW** · 02-20-2017, 04:25 PM

Are you saying that the injectors were replaced even after you have had this problem? Or did the problem come afterwards? Are you able to detect actual misfire in a cyclinder with INPA? I am not too familiar with INPA as I use BMW DIS and gives me individual cylinder misfire count.
I am not sure that engine smoothness is a direct relation to cylinder misfire. This may or may not be leading you down the wrong path.

Check for vacuum leaks:
- Get some FLAMMABLE brake cleaner, make sure its flamamble or it wont work. Spray around all the intake gaskets and seals including throttle body/ intake/ intake mounting bolts/ back near OSV etc...

Move coil packs around
- Move all the ones on the passenger side to the drivers side and see if you see any change on INPA.

Disconnect the MAF and start it, see if it runs any differently.

**thrawn5499** · 02-20-2017, 04:33 PM

I had the misfire and rough idle before the injectors were replaced. It seems to run exactly like before the plugs and injectors were replaced. I did get a misfire detected before with pasoft but not anymore. I have not been able to get dis to connect to the car. Maybe I need to try a little harder on that. I am going to get another new plug tonight and see if that makes any difference. I don't think it will. Also will try swapping some coils around but since they are all new I don't think it will be the problem. Could it be my cat? It seems to be isolated to the passengers side cylinders. I also rev'ed the engine while under the hood and while it does sound better at higher rpms, the misfire is still detectable.

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**SergeBMW** · 02-20-2017, 04:58 PM

Oh I didnt read that you had new coils. Scratch that.

Could be a bad cat or o2 sensor on that bank. Easiest way to check the cats is to run the car up to temp, get under and measure the temperature just in front of the cat and just behind the cat. Best to get yourself a laser thermometer. The front inlet should be cooler than the outlet. That is a normal working cat. If its cooler in the back then something has gone wrong with it. Compare to drivers side.

**thrawn5499** · 02-20-2017, 05:09 PM

Originally Posted by SergeBMW

Oh I didnt read that you had new coils. Scratch that.

Could be a bad cat or o2 sensor on that bank. Easiest way to check the cats is to run the car up to temp, get under and measure the temperature just in front of the cat and just behind the cat. Best to get yourself a laser thermometer. The front inlet should be cooler than the outlet. That is a normal working cat. If its cooler in the back then something has gone wrong with it. Compare to drivers side.

Ok I got the stuff to do that. Might be tomorrow or later before I can get to it. Thanks!

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**thrawn5499** · 02-21-2017, 03:23 PM

The more I think about this the more it seems the answer is right in front of me and I am missing it. If my problem is isolated to cylinders 1-4, what would control those and not effect 5-8? Injector relay? A wiring harness i forgot to connect? What would kill only one side and leave the other working fine?

On top of that it improves with more rpm's maybe too much fuel at low rpm's...

**mooll** · 02-21-2017, 03:34 PM

U did replace the injectors o rings right ?

**thrawn5499** · 02-21-2017, 03:38 PM

Originally Posted by mooll

U did replace the injectors o rings right ?

Yes I did.

**thrawn5499** · 02-21-2017, 06:22 PM

I tried hooking up again with DIS v44 but still get fault number 200.159. I can't seem to get it figured out. I don't know if it is the cable or something else. I am using the same cable as I do with INPA not sure if the same one works...

**psjr** · 02-21-2017, 08:55 PM

Temperature-dependent rough idle usually points to a vacuum leak.
However, your symptoms are so bad and so evenly across Bank 1 that I might consider suspecting something else. The fact that it is better at high RPMs would contraindicate a clogged cat, a common cause of a whole bank having issues.

However, it is easy and cheap to replace all intake gaskets and all vacuum hoses - I would definitely start there if you haven't considered it.

**thrawn5499** · 02-22-2017, 09:45 AM

While I want to get the car running, I don't want to spend much more on it since when I get it running it is going in long term storage and might end up being a parts car for my 2001. I would not have bought new plugs coils, injectors and hoses, if I knew I was getting the 2001. the car needs to drive an hour or so to my parents farm to go into a storage shed. I would prefer to not have it only firing on 4 cylinders when I drive it. Also there is a chance something could happen to one of my other cars and I might need this as a temporary back up. Thanks!

**thrawn5499** · 02-25-2017, 04:11 PM

Ok I changed the #1 plug today. I started it up and ran the smoothness test again.

After reving the engine a little

Then it started getting worse from there. Though the car was running better after about 5 mins #1 was back over 2000. A lot of the other numbers dropped though. I will post a pic from the computer shortly.

You can see even though #1 got bad again some of the other numbers dropped. I figured that was why the car started running better. Still want to get this figured out.

I shut off the car and pulled the plug again. Here is what I found.

Dry and black. This is after about 5 mins in the car.

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**thrawn5499** · 02-28-2017, 07:01 PM

Just thought I would post an update. I got the car running good again. I think it was a combination of a few things. Mostly it had not been ran long enough since changing the injectors. I think I may have gotten a little fuel in the engine when I changed them. I think this helped cause the carbon fouling of the plug shown above. Today after the car ran for 10-15 mins it was running a lot better. I took out the Number one plug and checked it to see if it was dirty again. It looked brand new still. I then took out #4 plug and it was covered with oil. I think I got it dirty before putting it back in. I cleaned it and put it back in making sure the plug well was completely clean. when I started the car it ran really smooth no more detectable misfire. No rough idle just a smooth running motor like I was expecting before I worked on it. Thanks for all of the help getting it going again!