We have a 93 400E that has become our problem child! This might end up being somewhat lengthy but please bare with me.
The car starts like normal every morning at approx. 1000 RPM and then drops to around 700-800 RPM (normal) and runs fine. It is driven 2 miles (3 stoplights) to the freeway and then is freeway driven between 10-15 mins. When exiting the freeway is when the problem begins.
As you slow at the bottom of the exit ramp the car's RPM begins to stumble dropping to 500RPM(very rough) and then it sometimes will all of a sudden jump to 1500 RPM. It all but stalls out completely at times and you wonder if you are going to make it through the intersection. These up and down RPMs continue for about 1/8 mile to the parking garage. But here's the kicker...never any issues on the drive home (even when needing to slow for backed up traffic)in the evening.
Then last week it did finally stall. I had driven it to the gas station which is approx. the same type of driving of going to work (10 mins. freeway). Ran fine until I got to the stop light at the bottom of the exit ramp. Then dropped to 500 RPM and was very rough. Made it into the gas station, filled up, and went to leave but only made it about 50 ft before it stalled. Started it right back up but would die on me immediately (happened 3x) with some help I got it pushed into a parking spot and tried to start it again in about 5 minutes. It started and stayed running but was back down at the 500rpm again (very rough). When I would rev the engine over 1000 rpm it would smooth right out but then drop back back down to that rough 500rpm range when I left off the accelerator. It never stalled again though, and after about 10 mins. of sitting there idling I notice that it was starting to smooth out and was running at 700RPM. So I said a "prayer" and headed for home. It ran great all the way home with no issues. I even kept driving it around the subdivision for a while once I was home "hoping " that for once the thing would act up on a trip home. Nothing..it seemed fine.
Then the other night my husband drive it around town (all city streets) for about 10 mins. to our local service guy. And sure enough it started acting up by the time we got there. Unfortunetaly, the guy was in the middle of something and couldn't come out at that moment with the testing equipment but when he tried it later, no issues (sorta like the drive home). Actually, I should say that while he couldn't get the rough idle to duplicate he did get some sort of fault on the crankshaft position sensor (I think that is what my husband said) Could this be the cause of our issues?
I have muttled my way through most of the threads that involved stalling issues. And I can add this to the info. This issue happens no matter if you are going straight, left ot right after it has been driven for 10-15 mins. Again, only in the morning never on the return trip home! Also, we tend to use BP (Amoco) fuel when we can.
We have done the following to the car in the past few years that would be related to the fuel system or ignition in some way:
Fuel pressure regulator - new(changed this thinking it might be the problem)
fuel filters - changed June 2003
fuel pump relay - 2-3 years old
caps and rotors - 4 years (approx 30,000 miles)
engine harness - 4 years
There may actually be more but my husband is at work so I'm depending on my own memory! (scary)
Thanks in advance for any input!
MB FRAU