Possibly a bad maf

[MNBoxster]

Hi,

I mentioned this in another thread, but start by reading your plugs. This is a diagnostic which has all but been forgotten on this day of OBDII cars where people rely more on scanners, but is still a very valid way of discovering what's going on directly inside the cylinder.

As mentioned, the codes you're getting will often not point to a particular problem. A fueling issue or bad MAF will manifest themselves in conditions which other sensors detect or cannot account for and so those codes are thrown instead.

Aside from fuel and air issues, I think there's a distinct possibility of a vacuum leak somewhere as well.

But, as I said, read the plugs. Whitish-gray indicates a lean A/F mix, Tobacco Brown is a proper stoichiometric mix and Black would indicate a rich mix. Go from there. Hope this helps...

Happy Motoring!... Jim'99

[ohioboxster]

Originally Posted by Gary Gaukler

One other thought: You said it stumbles at idle for a while, and then it goes away. That could be another indicator that your fueling is off. The first couple of seconds at idle the car is in open loop: the o2 sensors won't correct the A/F ratio until they have warmed up. Hence you are running off some standard fuel maps. Once the car is idleing in closed loop, the o2 sensors correct the mixture.

Gary,
That makes sense, would the maf have anything to do with fuel on start up when its in open loop? The interesting thing is the fact that after I reset the cel from the ecu the car ran fine. I let it sit for a few hours before I went to work and normally it would stumble on start up. Well, it didnt stumble at all but on the way to work the cel light came on. In the morning it stumbled a little. Its weird its getting progressively worse unless I reset the ECU. This kind of makes me think a sensor, not sure.

[ohioboxster]

Originally Posted by MNBoxster

Hi,

I mentioned this in another thread, but start by reading your plugs. This is a diagnostic which has all but been forgotten on this day of OBDII cars where people rely more on scanners, but is still a very valid way of discovering what's going on directly inside the cylinder.

As mentioned, the codes you're getting will often not point to a particular problem. A fueling issue or bad MAF will manifest themselves in conditions which other sensors detect or cannot account for and so those codes are thrown instead.

Aside from fuel and air issues, I think there's a distinct possibility of a vacuum leak somewhere as well.

But, as I said, read the plugs. Whitish-gray indicates a lean A/F mix, Tobacco Brown is a proper stoichiometric mix and Black would indicate a rich mix. Go from there. Hope this helps...

Happy Motoring!... Jim'99

Well here it is can you see it good enough?

[MNBoxster]

Originally Posted by ohioboxster

Well here it is can you see it good enough?

Hi,

Not the clearest pic, but the plugs look OK. This leads me to think vacuum leak, because whether it was fuel or MAF, either would affect A/F Mix, which by your plugs is good...

Happy Motoring!... Jim'99

[ohioboxster]

Yes, I felt the plugs looked good as well. Im pretty confident its not a vacuum leak I checked for vacuum leaks about a dozen times, the converters dont turn cherry red if the car sits and idles to temp and beyond finally the problem is only at cold start up. Its very strange and seems odd that after resetting the ECU the problem seemed to go away on the next cold start up and the stumble is far less than before resetting ecu. I ordered an Actron CP9135 so I can check which codes its throwing now. Considering ordering an LM-1, data logging software and doing a street tune. Need to check and see which is more cost effective between dyno shop tune or buying all the stuff myself.

[ohioboxster]

Originally Posted by Frank

Hi,
I recently had my MAF go bad.The car ran real bad on startup in the morning. It accelerated horribly and was just slow.I got the codes read at autozone and it said oxygen sensors,well it was the MAF and not the oxygen sensors to make a long story short. To figure out if that is your problem,just disconnect the wire for the MAF and it will put the computer into default mode,your car will run great if that's the problem.By the way,don't buy the bosch universal oxygen sensors if you ever need to replace any of them,they don't work .
Frank

Frank,
It worked! I pulled the harness off the maf sensor and the car started right up cold with no stumble. I kept it out of boost and drove it home with no issues. That was a great idea unplugging the maf! It kept the values set and allowed me to eliminate the maf from the equation, Thanks!