1990 735iL rough idle and vague steering wandering (archive)

My 735iL now has over 131,ooo miles and while it has had it share of repairs it stillruns excellent and I can't seem to justify a newer one for the money. While I have the usual self leveling and outside temperature failure (no heater core failure yet) and even a failed transmission 3k ago. I never seem to notice two problems that seemed to plauge 735 owners. One is a tendancy for the car to wander at highway speeds and the other is a rough idle that only appears after long periods of idling. About 3 months ago both happened at the same time.

I spent a lot of time going throught the archives and wanteed to pull together the information that I found in the archives and by experimenting with the car so that all of the information is in one archive.

First the steering. Even when I first bought the car the steering was never as tight as my 3 series and I simply chalked it up to the 7 having a reciprocating ball vs. the rack in the 3. Over time the steering got mor vague and the car would wander and follow the ruts and cracks in the road especially at highway speed. Eventually it got so bad that I didn't want to drive the car much at high speed. It was still tolerable at the speed limit.

The archives contain several items related to this topic and it was really just a matter of trial and error to find the right one. There was some direct loose feeling between what I did with the steering wheel and what the tires did so my first task was to reset the lash adjustment in the steering box. One full turn was apparently to much as I lost the ability for the wheel to center and finally ended with only moving the adjusting screw by a little less than one half turn. very small improvement. Still thinking my problem was in the column I tracked down the large nut at the very bottom of the steering column just before the shaft goes through the fire wall. This was not loose per se but I did manage to turn it one full turn which eliminated some fo the play between the column and the splined shaft. still small improvement mostly at low speed.

I put the car on a lift ( I restore lancias so I have a lift in my shop) and checked the tie rod ends and all of the the rods for that matter (everything checked out). Just before setting the car down I grabbed each tire at 12 and 6 (no play and at 3 and 9 and found lots of play in the drivers wheel. For those of you who have seen this it was a defective lower control arm ball joint (less than 30k on this one). Bought an OEM replacement this time, still pretty cheap from bimmerparts.com. steering fixed.

Next task was the rough idle and I would be slightly off base to say I have the problem fixed but I think I have it isolated. I should clarify that this problem only appears when the car is hot and has been idling for more than a minute as if the car is running lean or dropping a cylinder. Ten seconds after I pull away the car seems to clear it throat and runs perfect. As the car was about 40k off its last tuneup I gave it new plugs, wires, cap, rotor. no change. hmmm. I ran through all the checks on the TPS (mine is the six pin for the automatic) and it checked out fine. I pulled and cleaned the idle control motor whci helped some but not the final fix. checked the crank sensor which appears fine and spark from the coil looks good. pulled each wire carefully from the cap with the car running and each cylinder was contributing equally.

I pulled the air cleaner and started experimenting with moving the air flow meter vane by hand to get a feel for whether the car might be runnign rich or lean and decided that it might be a bit lean. I then adjusted the idle mixture screw in the air flow meter (very hard to get at) to as rich as it would go (screw bottomed out). This seemed to help but on a long test drive afterwards the rough idle seemed to return not quite as bad. I went back to the shop, opened the hood and pulled the air cleaner again to experminet with the air flow meter and within about 20 seconds the idle evened out (I hadn't touched anything yet, simply removed the air cleaner). I inspected the air cleaner element and housing, no problems. I even reinstalled the air cleaner and let the car idle for a half hour while the idle remained nice and even. I closed the hood and witin 10 minutes the rough idle returned.

The answer appears to be under hood temperatures and my guess is that it is the air temperature guage in the air flow meter picking up heat from the valve cover. For the recond I also bled the colling system (no air) in case it was an air hot spot near the collant temperature sensor. I am inthe process of figuring out a good way to insulate the bottom of the air flow meter from the valve cover and I will report back when I have more information. Any additional feedback is appreciated.

Tom Balon
1990 735iL, Damn I love this car!
1999 Jeep Grand Cherokee, damn poor quality
1965 AC Cobra Replica Twin Turbo, damn I hate winter
1958 Lancia Appia, built like a swiss watch

Follow Ups:

Excellent Article and excellent diagnostics alex lynch 14:14 3/25/2001 (0)
Re: 1990 735iL rough idle and vague steering wande Tom Balon 11:16 3/25/2001 (3)
- At least someone has had enough of BMW saying..... Rodzy 14:49 3/25/2001 (2)
  - Re: At least someone has had enough of BMW saying. Bryan Garner 16:59 3/25/2001 (1)
    - Re: At least someone has had enough of BMW saying. Rodzy 00:12 3/26/2001 (0)

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