Intermittent Stuttering & Stalling
 

Hello. I have a 1997 850 that is having some issues.

My buddy sold me this private sale. It ran perfect for a few months. Then one day, I was driving home and it started bucking pretty seriously. I threw it into neutral so it wouldn't jerk the car, and it stalled. It was a pain getting home.

When you first start it, it will run fine for maybe a minute. Then it will heavily bog down and the rpm will fluctuate wildly. I can usually keep it running by modulating the throttle, but it's rough. It will do that for a few minutes, then go back to running fairly normal, and repeat this cycle. The weird thing is, even when it's not fluctuating, it will run very rich.

It's not throwing any codes. In the below video, the CEL is on but it always is for the first minute or so the car is on, then it goes off. I've scanned it with my Actron OBD-II tool right after it starts, but it throws no codes at all.

Here is a list of things that have been changed on it recently, to no avail:

• Up and Down stream O2 sensors
• Fixed a couple vacuum leaks
• Fuel Filter
• Dry Gas
• Cleaned MAF sensor with iso alcohol

Here is a video of how it acts:
I'd really appreciate any help I can get. Feel free to ask questions, because I usually forget things. Thank you.

Check your fuel pressure at the rail.

Checked the fuel pressure; it's perfect at 44.

The car finally threw a code. Don't know what jump started it.
It shows an MAF Circuit High Input code. I cleaned the sensor with CRC MAF cleaner, and it helped a little.
I'm having a new one arrive tomorrow and we'll see what that does.

And when it starts dying does the pressure change?

Boxpin's advise is sound - you need to watch the pressure over time with a guage. When my 850 started randomly stalling I replaced the fuel pump relay to fix it. Problem is, fuel pump relays can fail when the pump is drawing too much current so true to form, it was a matter of months before the fuel pump started to fail outright. It would show normal pressure for a while then the pressure would drop off and the car would stall or be hard to start.

I was surprised to see that it stayed at 44 even while dying.
I had fixed a small vacuum leak at the regulator that I fixed before I tested the pressure. I don't know what the pressure was before that but it didn't run much better after it was fixed.

I replaced the MAF sensor and it runs like a dream now. I also found a thick gauge engine ground wire disconnected (rust), so I reattached that. Maybe that shorted something out.

Going to throw all new plugs in and call it good.

Thanks for the help.