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2000 SE has been acting up, cutting out, etc. I'm getting seriously fed up with working on this thing. In the last two months I've replaced the a/c compressor, starter, plugs and wires, O2 sensor, fuel and air filters and cleaned the MAF and electrical connections. It still has an intermittent miss, stumble, cutting out whatever you want to call it. Even after replacing the O2 sensor it's still throwing a P0420 code. Any ideas on where to go from here?

We did sort of leaving you hanging here http://www.pontiacbonnevilleclub.com/fo ... 828#p24828 and it probably would have been better to bump that one.

Have you tested the TPS to see if it responds smoothly? Did you mention the P0420 code earlier? If it is stumbling as the RPMs climb, in particular if you get on it a bit, coupled with that code, you could have a plugged cat.

I did post "updated" on the other thread but didn't get a response. Sorry, I'm just getting a little frustrated with the situation. I had mentioned the code in an earlier post before replacing the O2 sensor. I had the cat replaced with an aftermarket one a couple of years ago. I guess it could be a bad one. How do I test the TPS?

It's easiest to check with an analog (with needle) meter, set to watch the resistance. It should vary smoothly, without any dips or sudden rises, as the throttle is increased. Seeing you have a scantool, you can watch the voltage and/or angle for the same thing.

Forgive my ignorance but I don't understand what you're saying about using the scantool to check it. I did pull it and connected a standard ohm meter to the prongs of the TPS and the needle moved smoothly throughout the range while moving the spring inside the TPS. Sorry I don't know all the technical jargon associated with these things.

It's ok, we all have to start somewhere. He meant that you can use your scan tool to watch the TPS voltage and angle, and make sure that it wasn't going from, say, 15% open and jumping to WOT or something. Or when you go to WOT it would say 15%, etc. But since you did that with an analog volt meter, you are good.

OK, I'm not sure my scan tool will do all that or maybe I just don't know how to use it. All I can do with it is pull codes, it's just a cheap OBD II Scan tool.

A little more info. I experienced the cutting out while idling today but it never seems to happen at highway speeds. Don't think its the cat because it runs fine when you get on it.

OK, so then you have a code reader, not a scanner. There are several things that could cause your problem. You could have an intermittent crank sensor causing your your problem.

i had the same promblem..did the tune-up..fuel filter..ect. it was the mass air flow sensor! hope that helps if you havent fixed it yet!

What I would look at

1) Vacuum lines. As the lines get old, they can look fine but be brittle and leak. Since you can't reliably repeat the behavior, try a "wiggle test" of the vac lines. Take each one, one at a time and while idling, wiggle the line and the connectors where it's attached. As you wiggle each one, see if there is a change in idle. If there is, that could be the culprit. If you can attach a vacuum gauge on the motor while doing this test, you may see a vac difference that doesn't necessarily affect the idle, but you may see a change in vacuum that points to a possibly bad line.
Cost $0 and some time

2) Yes, the MAF could be it as well. This could be a problem to test. You can try a "tap test" of the MAF. Using the handle of a large screwdriver, gently tap the MAF while the car is idling. If it stumbles, this would be the problem. The Tap test doesn't always show a bad MAF, but it can.
Cost $0 and a little time

3) Again, the MAF. Do you have access to a known good MAF to replace the current one? If a buddy has one you can borrow for a day or so, try replacing the MAF with a known good one. If the problem goes away, this is likely it.
Cost $0 and a little time and a good friend with a good MAF (that's the tough part)

4) Crank Sensor. A failing crank sensor can be a finicky part to track down. It will progressivly get worse until it fails and leave you stranded. The easiest no cost check here is mainly visual. Is it in tact? Are the vanes of the sensor broken at all? If there's any sign of damage the the 3 vanes of the sensor, that's the problem. If there's no visual damage, you can check one more thing on the crank sensor. The clearance. Typically, a crank sensor will have the clearance of about a matchbook cover between the vanes on the sensor and the interruptor ring that goes between the vanes. Using a matchbook cover or some other similar very flexible material (a plastic presentation cover, etc), slide the matchbook cover between the vanes and the interruptor ring. DO NOT FORCE ANYTHING HERE!! IF IT DON'T FIT, DON'T USE IT!! You can damage the sensor by forcing something in here. But if the material fits, it should fit evenly between the vanes on both sides of the interruptor ring. If it doesn't, either the sensor needs adjusted, or it's bad and needs replaced. The interruptor ring should never hit the vanes of the sensor.
Cost $0 and some time

These are based on a driveability issue. The P0420 code is not necessarily indicative of these parts, but then I had a TPS code due to a vacuum leak once....go figure. So, lets look at the code. Here's a page with info on the code and some things to look at: http://www.obd-codes.com/p0420 Have a look there and see if anything there is part of the problem/solution.

Hopefully this gives you some things to look for that will solve the problem.

Been out of town a few days and the problem is getting worse. It is occurring at highway speeds now. Thanks for the great info and the suggestions, I will begin testing ASAP. BTW, where is the crank sensor located and how hard is it to swap out?

Well, it's not the crank sensor. I put a new one in it and I still have the same stumble/miss. BTW I don't see how you can check it while installed since the crank pulley has to come off before you can even see it. Did the tap test on the MAF and it doesn't appear to be the problem. I don't have anyone around with one I can swap out to try. How many vacuum lines are there? I want to make sure I'm checking all of them. Could the problem be the result of dirty injectors or would that cause it to bog down. I still haven't ruled out the catalytic converter. That may be my next move. Another question is, could it possibly be an ignition coil? Is there a way to test it?

Finally found the problem! Unfortunately it was after replacing a bunch of other parts. I returned to the MAF for another "tap" test. I found there was one spot where, if I tapped it with the handle of a screwdriver, it would stumble/cut out. I replaced the MAF and it has been fine since. Thanks to everyone who gave tips and made suggestions.

Glad ya got it fixed!