'88 735i transmission problem

[jlfulton51]

I am looking at a 1988 735i that is immaculate and seems to have had exceptional care (garaged, etc.) but the transmission jumps our of overdrive occasionally. If you shut the car off for 10 sec., it is fine again. Is this the ECU, throttle position sensor, or internal?

[witeshark]

After the 10 second shut off, how long is it good for? What kind of driving? Do you have access to the service records, and how many miles on the tranny?

[jlfulton51]

I haven't been able to drive it myself yet. The owner just says "occasionally". The transmission has 143,000 miles on it.

[jlfulton51]

Here's a little more info on the '88 transmission problem. It only shifts out of overdrive when you first are getting up to speed. After you shut if off for 10 seconds your good. It doesn't do it again. The car has only been driven about 1,000 miles in the last 5 years.

[jlfulton51]

Thanks for the previous response.
Now that I have this car, I can be a little more specific. The car has 152K miles on it. From the records, it has been serviced well with not previous transmission problems. There are not leaks under the car. I drove it a 1000 miles home. At first it would correct the problem of shifting back into drive by shutting it off for 10 seconds. Then no more problem until you stop again. Later in the trip it would shift back and forth from overdrive to drive a few times, then settle into drive and stay there. After The last time I stopped for gas, it acted like it stayed in drive when I started out rather than starting in 1st. Ocassionally, going down the interstate it would shift into OD, then back into drive and a few times shifted into passing gear for a second. Eventually, it stayed in drive even when I got into town. I hope this helps. Can you please discern anything from this?

[witeshark]

I think one thing I'd have a look at is the throttle position sensor.

[jlfulton51]

Thanks so much for your help. That verifies other recommendations. I'll do that first, and let you know the outcome.

[jlfulton51]

I replaced the TPS and the transmission worked well about 20 miles of interstate and around town the next day. However, the idle was around 1,000 rpms. We took another 30 mile drive the next evening. When we stopped and I got out for about 15 minutes, my wife said that there was some sparking or static sounds under the passenger side of the dash. About the third time we stopped at a light it stayed in drive instead of shifting down. I just check the TPS again for resistance when the throttle is operated and the resistance doesn't change.

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[jlfulton51]

Here is where I stand with the 88 735i transmission. I have changed the ECU with a used one, and nothing has changed. When I start out in the morning it is always fine. After it is driven awhile it will start shifting from drive into third. Eventually, it will not shift out of 3rd. When it first starts acting up it seems to help by shutting the car off for 10 to 15 seconds. When I start out again, it will be fine for awhile, but as the day goes on, even after leaving it parked for a couple of hours, it gradually gets worse. The transmission warning "ding" becomes constant, and it will not shift out of 3rd. After sitting over night, it will be fine for awhile the next morning. Could this be the valve body? or an internal solenoid? If so, is it possible to fix it without rebuilding the transmission?

[taze]

I am in an identical situation with the same problem you describe in your thread of several years ago. I did not see the resolution to the problem. Can you help?