Volvo 850 CEL - need to diagnose

Suddenly run into an issue with my '96 Volvo 850GLT wagon. Car has 133k on it.

A few weeks ago, my nanny was driving, and she said that the car sputtered for a few seconds and the CEL came on. Other than that, she said it drove OK. I tried to tell her that she was wearing too much clothes and the car sensed it, but she didn't buy that story... So, thoroughly dejected, I went out to check the car. It started right up, but within a few seconds sputtered badly and stalled. Fired back up and stalled again. Let it sit a few minutes and went back out. Then it fired up and ran great for a bit. Until it stalled again. At that point, it was the night before I left for a business trip. It sat for a week. Towed it to the mechanic when I got back as it was due for inspection anyway. They pulled the code and said the MAF was bad. Put a new one in.

The next day after leaving the shop, the CEL comes back on. The car is running better in that I don't feel any more sputtering while driving. But it's now harder to start when it's cold. It'll take an extra crank, sputter for literally a half second then run fine. Starts OK when warm. Also now hearing detonation under part throttle, goes away when I lift off the gas or hit it hard. I pulled the code at Autozone yesterday. It's now saying bank 1 (it's an inline 5, so not sure why it's saying "bank") is running rich. That would probably explain the hard cold start, it's being flooded?

Any idea what's the cause? I don't want to throw parts at it until we get the right one. How to best determine what's really the issue? Pressure regulator perhaps?

Its also possible that Bank 1 (thats just the way they do it- on a single O2 sensor system, there is only B1) is actually running lean because the O2 sensor has gone south. Its reading richer than it actually is, starts pulling fuel out.

Or, on a car of that age, sometimes it takes a while to get the adaptive memory reset to normal. If the MAF was off, it will have been altering the fuel trims, and is taking a while to head back from there.

Or, you cheaped out and bought a remanufactured aftermarket MAF instead of a Bosch or Volvo branded unit, and its junk.

I'd head back to the shop that did the work and get them to check whether they are finished...

Wiggle the MAF connector while it's running and see if it hiccups, it's a known problem with these cars. If the connector is the problem, you can get in there with a pick and tighten up the connectors. When you put the plug back on put a sip tie around the base of the plug and hold the maf wiring to the base with it, this keeps the strain off the maf wiring.

Also, could be a bad fuel pump relay, you'll have to unscrew the cover of the fuse panel to see it. It will be the relay in the middle with 103 marked on it. If it's green, it's the original relay and should probably be replaced by now as they have a problem with the solder joints at this age. If the relay case is pink, it's been replaced.

Shawn

Thanks for the tips, I'll check those out.

I'm not sure what brand MAF he put in, I'll have to ask. I was wondering it the cars' adaptive memory had anything to do with it. I was guessing not, but I'm not sure.

Bringing this back up as I'm still trying to chase down the problem. One pattern I just noticed. The engine detonation/knocking is very dependent on ambient air temperature. In the morning when it's cool, there's very little detonation if any. Yesterday on my drive home it was 90-92 degrees and it was knocking like mad if I was at partial throttle. So, we have:
Hard cold starting, starts fine when warm.
CEL saying engine running rich (though oddly enough, my fuel mileage has gone up by 1+mpg recently).
Ambient air temp sensitive detonation.
All of which started after changing a MAF due to engine sputtering/stalling (which has now stopped).

What's going on here?

Temp sensor? Or O2 sensor is where i would start.

Klayfish wrote: So, we have: Hard cold starting, starts fine when warm. CEL saying engine running rich (though oddly enough, my fuel mileage has gone up by 1+mpg recently). Ambient air temp sensitive detonation.

All these seem to indicate a lean condition. The fact that the CEL says running rich even when mpg is going up points to several things.

Since you have already changed the MAF I would look at the O2 sensor, temperature sensor, and maybe the IAC (idle air controler) in that order.