735i (M30) Running Rough

[twhitestone]

Hello,

I have a 1988 735i (with the M30 straight six 3.5L) and I am having a problem with it running rough. It seems to idle smooth, but as soon as you give it any gas the engine runs roughly. It is driveable, but unpleasant. I did discover that if you take off from a stop and accelerate rapidly (to about 3500 RPMs) the problem goes away for a time while driving (15-30 mins.) but will come back either 1) after you turn off the car or 2) after a short period of time (30-90 mins.) elapses. Anyone here had any similar experiences, or perhaps insight to point me in the right direction for troubleshooting? I have replaced the spark plugs, checked for air leaks upstream of the MAF, and tested the idle control valve, they all checked out fine. Thanks!

Tom

[bmwstyle]

maybe its your fuel pump or fuel lines....

check that out.

[1988735iLBrooklyn]

Had the same problem brought the car to a mechanic and said cylinder one was not firing properly.

So discovered that on of the rockers was broken. But the car still ran but rough.

We replaced all rockers then cam shaft.

Brought the head to a machine shop for them to grind it.

Works like a champ now.

Total cost.

$1410.00

12 Rockers at 385.00
Cam Shaft 375.00
Machine shop for head 250.00
Labor about 400.00

[csieminski]

When I had my 528e, the fuel pump failed from one moment to the next--ie I drove the car, shut it off, and when I tried to restart, the car cranked and cranked, but would not fire because the pump had simply failed. So from my experience it doesn't sound like a fuel pump problem.

I did recently have a problem with oxygen sensor needing replacement, and my 535i demonstrated similar behavior to your 735 prior to replacement. Is the check engine light on? I'm suggesting this because O2 sensors apparently require replacement every 60K miles, and a malfunctioning one will cause the car to run rough as well as at a loss of power.

[wizzordrb]

Originally Posted by twhitestone

Hello,

I have a 1988 735i (with the M30 straight six 3.5L) and I am having a problem with it running rough. It seems to idle smooth, but as soon as you give it any gas the engine runs roughly. It is driveable, but unpleasant. I did discover that if you take off from a stop and accelerate rapidly (to about 3500 RPMs) the problem goes away for a time while driving (15-30 mins.) but will come back either 1) after you turn off the car or 2) after a short period of time (30-90 mins.) elapses. Anyone here had any similar experiences, or perhaps insight to point me in the right direction for troubleshooting? I have replaced the spark plugs, checked for air leaks upstream of the MAF, and tested the idle control valve, they all checked out fine. Thanks!

Tom

Sounds like the problem i had with my 735i...ideal control valve?

[twhitestone]

After many months of struggling with this intermittent problem, I brought the car to BMW for them to look at it. Turns out it was a bad fan clutch - it was causing weird vibrations through the cam shaft. All better!