E34 540/6-Engine running very rough

[540ii]

When I start my e34 and the motor is cold it runs very rough and the Check engine light comes on. The problem really goes away once the car is driven for a few minutes, except it does seem a bit rougher at idle and makes a rattle noise when it is cold. Any advice on the source of this problem is appreciated.

[Fetch]

Assuming no Nikasil issues & that it's getting colder in your area,
The intake gasket(s) are probably leaking on your engine.
They leak less when warm because they swell up a little.

One source of possible rattling besides engine related: Does it only do it when the engine is idling rough/stumbling? Manual transmissions can make noises like that at very low RPMs. Try pushing the clutch in when it is making the rattling noise. Just throwin' the idea out there.

[540ii]

Thanks for your advice...It seems motor related

[Alpinewhite]

Thanks for your advice...It seems motor related
95% it is intake leaks and/or mucked up PCV plate. Many M60 people have it every winter.

[Tiger]

Ditto on ICV plate... Also the intake manifold gasket leak.

[winfred]

check what code it's throwing, 02 sensor related codes usually point to the pcv plate/intake plenum leak, air mass sensor codes usually mean crapping out air mass sensor, both are fairly common on v8s

[632 Regal]

the rattle might be either the canister draining back into the oil pan or too thick of oil (most likely). Change the oil to 0w-40 and see how it runs after a computer reset.

[Antrieb]

I concur with the above.

Here is a parts list of what you need. This job is fairly simple and is outlined in the Bentley Manual.

13541747475 - ASC only O ring
11617501562 - PCV plate
11611437694 - cap
11611747085 - cap
11611729727 - front manifold gasket
11611729728 - rear manifold gasket
11151736140 - O ring
11611433328 x 4 - cylindar head gaskets
11611736648 x 10 - bushings


Here is the procedure if you don't have the Bentley

1) Disconnect the battery
2) Remove the engine cover and the ignition coil covers.
3) Disconnect the ignition coils by pulling out on the silver retaining clips, then lifting up on the coil connector. Leave them hanging.
4) Remove the air intake boot from the air box and the throttle assembly.
5) Pull the air regulating valve from the throttle housing. Silver, cylindrical shaped. There is a rubber bracket holding it to the accelerator cable bracket.
6) Disconnect the throttle cables from the throttle assembly. You can try to remove the two T30 torx bolts that hold the bracket to the throttle assembly. I had no luck here, so just pinch the plastic tabs and work the cables out through the slots. Lay the cables over by the brake fluid reservoir.
7) Put towels underneath the input and return fuel lines and disconnect them from the fuel rail. The return line is a beast to get off, as it is really tight in there. I just cut mine and replaced it new.
8) Disconnect two hoses on the underside of the throttle assembly. These are easily accessed.
9) Remove the injector harness connections from each cylinder bank. There are three for each bank. Label them appropriately, as they will be moved around a lot. Just pinch the wire clips and lift up to disconnect.
10) Disconnect the connector to the throttle assembly, on the passenger side. There may be a similar, three-pole connector that is hanging there loose. I do not know what it is used for. Label both so that you know which one is used, if your car was set up like mine.
11) Disconnect the sensor connector from the intake manifold. It is at the front side of the manifold, on the passenger side.
12) Remove four 10mm hex nuts, two on each side, from the injector harness wire boxes.
13) Remove the injector harnesses. I tried to use a dentists pick to loosen the wire spring clips, but with no success. Per Whit’s suggestion, I used a large, flat blade screwdriver. Wedge it between the harness box and the fuel rail and ever so gently apply pressure to loosen the connection to the injectors. Work one injector at a time so as to not damage the plastic ears. Lay the driver side harness over by the air box to keep it out of the way. It remains attached to the passenger side harness.
14) Remove the two 10mm plastic nuts that hold the coolant overflow tank to the firewall. There is no need to remove the tank, just loosen it and let it hang there.
15) Remove the ten, 10mm nuts that hold the intake manifold to the engine. Use needle nose pliers to pull the nuts up, so they don’t fall down and get lost. Also pull out the ten sleeves that line the intake up on the mounting studs.
16) If possible, have an assistant hold the coolant overflow tank up out of the way while you lift off the intake manifold. It comes off with the fuel rail and injectors still attached. There is no reason to remove the injectors unless you want to replace the o-rings while you are in there.
17) Lift up on the manifold from the driver side, then slide it toward the firewall to disconnect the oil pipe from the PCV plate. There is a metal bracket that is on the end of the oil pipe that you just lift up on with a flat blade screwdriver and slide back. It is tight in there, but doable. Remove the manifold from the engine as an assembly and place on a clean work surface.
18) Now is a good time to get out the shop vac and clean out the debris in the valley. Most of the stuff in mine was just flaked off cosmolene from the valve covers. You will want to get all the crud out of there so that it does not fall into the valve train.
19) Clean the surface where the manifold mates with the heads using a lint free cloth.
20) Time to disassemble the intake manifold. As per previous posts, the T30 bolts will most likely be tight, and the heads may strip when you try to loosen them. If you had luck getting off the Bowden cable bracket from the throttle assembly, then good for you. I had to bend the ear of the bracket to get Vise-Grip pliers in there to get the bolt loose. In fact, just about all the bolts had to be Vise-Gripped loose. You can replace them with M6 hex head bolts.
21) Remove the six T30 bolts from the throttle assembly and the seven T30 bolts from the PCV plate so you can replace the gaskets.
22) The front and rear gaskets look similar, but the front side one has a slight indent on the bottom side. They will fit perfectly into the slots in the intake, so be sure to mark which gasket is front and rear.
23) Install a new PCV plate and cap along with the gasket. The cap is purchased separately. The PCV plate will come with a new o-ring for the oil pipe.
24) Replace the four gaskets on the underside of the intake after cleaning the mating surface.
25) When installing the intake, make sure that the oil pipe is reconnected to the PCV plate. To do this, push the pipe as far forward as possible, then lay the intake into the engine, pushing it toward the back.
26) The injector wiring harness connectors get moved around a lot. Be sure that you have them secured out of the way so that they can be routed back for installation.
27) Work the oil pipe into position in front of the nipple of the PCV plate. Use a flat blade screw driver to push the pipe rearward so that the firewall end engages with the PCV plate, then work the clamp into place, so that the tab locks over the ridge of the plastic.
28) Install the ten alignment sleeves, then the ten nuts for the intake manifold. Torque it to 11 ft. lbs. from the inside out, alternating sides. After torquing the nuts, go back and retorque, just to be sure.
29) Install the injector harnesses. One of the connectors on mine turned a little so I lifted it back off and aligned it prior to pressing it into place. It takes just a little push to get it to lock in.
30) The remainder of installation is the reverse of the removal.
31) Upon first restart, turn the key to position two and let it sit there for a few seconds before trying to start it. Most, if not all, of the fuel dumped out of the fuel rail and the system needs to re-pressurize. It will run rough for a minute, then smooth out.
32) Drive and check for fuel leaks.


Tool/supply list that I can think of:

1. 3/8 socket wrench
2. 10mm socket (3/8 drive)
3. A few parts bins (tupperware works fine)
4. Permatex (liquid gasket) - good for holding on the gaskets so they don't fall into oblivion (kind of like glue)
5. Case of your choice beer
6. Extension magnet for when you drop the nuts into your engine bay