I replaced the MAF on my 3100 engine, (although I had no codes) now the car runs really bad, erratic idle especially. Am I supposed to reset the ecm, and if I am how do I reset?
This car is driving me nuts!

 

Hi G,
Did you replace your MAF sensor with an AC/Delco? I replaced mine with an aftermarket one and had the same symptoms as you, then it got to the point where the car would run until the Temp reached 160° then the car would just Die. And it would not start again until the engine cooled. Once the Delco MAF was put in, the car ran fine.
Have you tried to put your old MAF back in? What was it that caused you to want to swap out the MAF? Maybe one of us can help you figure out what is going on if you give us a little more info on your symptoms before the MAF swap!

 

First, my biggest question....
Why did you change the MAF? Unless you have a condition that diagnostics indicate it has gone bad, then you don't need to change it.
Second, as JC pointed out, brand of MAF can be important (as not all brands put out the same values as the AC Delco ones).

 

No I didn't replace it with a delco. I did put the old maf back in.
Ran a scan using a snap on Modus scanner. Nothing showed up, everything seems to be in spec. BUT the car does not run right, seems to be searching for the right fuel air/mix at about half throttle, up to around 3,000rpm. then runs normally. DOES NOT do it when the car is cold. But as soon as it gets warmed up, it starts to stumble. New plugs, new wires, new filter, new oil/filter, cleaned EGR passage, used propane to search for vacuum leaks, vacuum is steady. replacing the MAF was just an educated guess from the symptoms, from other techs and from what I've read.

 

Gbrown, I would suggest with modern cars don't just start replacing parts hoping to fix something. First, you say it runs fine cold but once warmed up it "stumbles". With no check engine light I would do a compression test; make sure all 6 cyl have good, and relatively close numbers. When I was trying to solve my rough idle problem one thing I did was remove the entire throttle body and gave it a thorough cleaning. I was surprised at how dirty it was behind (downstream) of the throttle plate.

Good luck.

 

When is the last time the O2 sensors were replaced?

Edit: (just read your post again.) When scanned was it just a search for codes or did you get any real time data with the car on the road? You may have a bad connection at the MAF from road vibration. If you do you should detect voltage signal fluctuation. The PCM would be constantly trying to compensate for the signal changes.

The reason I mentioned the O2 sensors is the air/fuel mixture is calculated off a voltage signal from the temp switch until the engine is up to temperature. Then the air/fuel mixture is calculated using the O2 sensors. If either has an accumulation of carbon on it the voltage signal will fluctuate. The PCM will constantly be trying to compensate for the voltage changes. This can happen without triggering the CEL. If you don't find a bad connection in the MAF wiring harness I would check the harness for the O2 sensors. If they have over 65K on them I would replace them.

 

It could be a MAS problem. Mine had issues when the engine reach NOT. But you could also have a clogged injector or fuel rail issue. 03SSLE has a very good handle on these cars. The_Maniac knows a lot too and has Shop manuals.
I agree, don't swap part hoping one will fix the problem. That could get very expensive. You can get a BLUETOOTH OBD II Scanner and Torque II app for your for. You can read codes and get real time info. It may not help you for this issue but it is a great tool to have!

 

I already got real time info. using the snap-on tools scanner. O2 sensors were fine, everything was in spec. (except right front speed sensor for the anti-lock, but I already knew that) Car idles so smooth you don't know it's even running. Throttle body is clean. Remember, I put the original MAF back in.
Here's the latest thing I've discovered, I removed the EGR solenoid and made a blocking plate, then put the egr back on. Car ran great, well at least as good as it did before the issue. Took the plate out reinstalled the egr and produced the same problem, what do you think? Do I need a new egr solenoid?

 

1998 Monte-Carlo 3.1eng. 125,000+mi.
I've been dealing with this sort of stumbling on acceleration for awhile. Originally started with an egr code, erased code, didn't throw the code again. Then started really stumbling on acceleration up to 3,000rpm, but idled very smooth, no misfire. Installed new plugs, new wires, cleaned throttle body, cleaned egr passage, compression good, no dtc. Went over the engine with propane gas and a hose and found no vacuum leaks. I then got a friend who is a tech to use his really expensive Snapon Scanner tool, and found all sensors to be in spec. I went full circle and came back to the EGR. As a side note I did clean the EGR pintle too. I took the EGR out and put a 9volt battery on the terminals and could see the pintle move in and out, although that's not an indication that the valve is completely closing.
I then decided to make a plate to cover the EGR openings, and reinstalled the EGR solenoid. Went for a drive. The car ran like it did before all of this started!
Soooo after this long story I'd like to ask all of you..does this sound like the EGR solenoid needs replacement? Remember, I don't have any trouble codes and live data scanner says everything is in spec.
Thanks a bunch!

 

Check fuel pressure also. You could unplug the EGR and see if that makes a difference too.