1996 318i 5 speed M44 engine runs on at higher speeds only
 

96 318IC M44 engine
92,000 miles 5 Speed


Engine runs on at speeds over 65 mph in 5th gear, you take your foot off the accelerator and the mpg (vacuum Gage) does not go to the left right away. It sometimes flutters but never shuts off the fuel right away.

At all speeds below 65 and even above 3,000 rpm it works perfectly. Higher rpm in lower gears than top have no problems.


Things I have done or checked.
Last was change the DISA o-ring, the old was flat in 2 places. Checked the DISA with 12 volts flap snapped shut. Sucked on the vacuum line from the bottom of the valve closed and stayed shut.


Cleaned the throttle body, cleaned the idle air control valve. Engine idles perfectly and runs perfect except on the highway and then only when trying to slow down.


The throttle cable appears to be fine at lower speeds and constant shifting there is no problems so I ruled it out.


I am currently stumped at what the cause could be. Fuel pressure? The fuel filter was changed a bit ago. Nothing had been done to the engine recent to the problem being identified. Any help would be greatly appreciated.

I would check the fuel pressure, maybe scan the obd.

Scan it and check for pending codes

Thanks for the info I did have the OBD scanned and there were no codes. Without a loss of power I was doubtful that the fuel pressure would be low. I am constantly looking for any vacuum leaks but have found nothing yet. The around town driving still has not deteriorated. I was hoping something would change to give some indication.

I was wondering if a dirty injector could stick open and cause the engine to run on? Thanks again for reading.

A stuck open injector would likely cause a rich code, and a vacuum leak would set a lean code. Does the car have cruise control? If so, I would try disconnecting the cruise control cable at the throttle body. Perhaps the cable is binding and hanging the throttle open. Hope this helps.

Thanks for the suggestions.

I took the cruise control cable off as suggested by bluoval6, unfortunately no change. This is how it performed with the cruise cable off.

At 65 mph about 3000 rpm it ran on for a few seconds never slowing at all till it bucked a little then started to slow.

At 70 mph, about 3200 rpm it ran on for a long time. Finally I hit the clutch and the rpm's increased. It started to slow after quite a few seconds.

Afterwards in traffic it seemed to take a long time to go from 1000 to 750 rpm or normal idle.

Would a stuck open idle control valve cause these symptoms? It seems to only be happening when the secondary air is in use. Any suggestions what about the throttle cable? I would think that would be problematic at any speed.

A sticking IAC would be my next suspect. I believe secondary air only runs for the first few seconds after a start-up. Did the issue start when the weather turned cold? It's my experience that IAC valves like to act up more in cold weather.

bluoval6 You are the best that was it. I immediately disconnected the electrical plug and headed for the highway. Problem is completely gone. It does not idle any different it just shuts the fuel off more abruptly. The IAC must be stuck open when energized, it can't be open without power or the problem would not have gone away. It did have a spring return I noticed when cleaning it. I had cleaned it a couple of times because I suspected it too. Just never thought to disconnect it and try it. The car up until the last 2 years was in Massachusetts now it is living in Florida with only part time use. It worked fine till 6 months ago when I was taking a highway trip, and it started to not slow down. Using it mainly around town I never got around to getting it fixed. Thanks again for the solution. Now I have to install a new set of tie rods and it will be back to 100%. Such a fantastic car and a vert to boot. Bob

Glad to help!