started a few weeks back and seems to be getting more frequent......hard to describe, only under driving power it seems to be like a very lite buck or miss. have reved up the rpms in park and engine will not miss or act up. it seems to only do it under power when in gear, I can hold the brake and give it gas and the tach gauge jumps like its missing and the engine sputters not bad but does sputter like its losing either fire or fuel. any ideas.......... driving down the road at any speed it like has a lite bumping or slight buck to it. im stumped. recently changed all plugs, wires, filters and oil. no help in that.....still doing it.
2001 model ls 3.4 ltr engine


please help if ya can, thanks

 

What kind of Monte do you own?

 

I have a 2001 montecarlo ls with the 3.4 engine.

 

Your car has a rev limiter in park, so it will jump and bounce. You aren't supposed to rev in neutral or park.

When you are driving, could have a Cat going bad.

 

Hate to give you bad news but mine did the same thing and i changed the same stuff and it turnd out to be the lower intake gasket! it was sucking in air.

 

To add to that, if you do a search, you can find info about a GM bulletin of extending the warranty on factory cats. If that is the source of your problem, you may soon be hitting that extended warranty limit fast!

As Chibi mentioned, you have a rev limiter, so when revving it high, it will reach a peak and not let you go any further. In all honesty, anytime for diagnostics that you need to rev a car in neutral or park, you should never need to rev it much.
Since the cat may still have an extended warranty, I would see if a dealer can inspect that FIRST (and wast NO time about it).

If it's not the CAT, here's what I would look at next:
1. - Inspect each plug wire for damage. If they are really old (such as factory original), this is probably a good point to change them.
2. - Inspect the plugs. Factory irridium plugs I believe are supposed to last about 100K miles. We bought an '05 Impala this past December with 150K on the factory plugs, no performance problems. Regardless, I changed them with Platinum NGK plugs (the original AC Delcos I pulled out were re-branded NGKs, as they had both AC Delco and NGK markings). If the plugs are old (again, factory original), it would be worth changing them.
3. - Possibly a intermittant failing coil pack.
Here's a link from the Bonneville guys for inspecting the coil packs:
View topic - Comprehensive guide for troubleshooting Ignition coils : PontiacBonnevilleClub.com
I have yet to use that coil pack write up (I did not know of that method at the time I had failing coils, so it was old trial and error).

The last item on my list might be a failing injector. I've been lucky (if you can call it that) when I've had an injector fail, it exhibited rough idling. A friend with a GM Tech II scan tool was able to shut off 1 injector at a time (searching for the one that causes no change or the least amount of change in the engine idling).

Hope this helps!

 

if this was the case it would probably be doing it also in park when revving I would think because it would be sucking air in all the time

 

I'm not going to say that the OP's problem is or is not the LIM gaskets, but I think it's premature to come to that point. There are some diagnostic steps that need to be done before jumping to that conclusion.

What you described as being a LIM problem with sucking in air sounds like a vaccuum related problem. One could use a vaccuum guage to check if there is a problem. But, I would think the performance problem would be more noticable, less intermitent.

LIM gasket failure is very common on the 3100/3400 engines. My experience with the LIMs is it will cause oil and coolant leaks, not performance problems (unless the gasket problem begins to allow coolant and oil to mix). A couple of ways to find LIM problems on a 3100/3400 is to inspect the base of the LIM to see if there are signs of coolant or oil deposits. Another way that helps is to put a radiator pressure testers on and check for leaks (most the time, you will loose pressure and find where a seal on the LIM is no longer holding).

I think so far the OP is best looking at the CAT and ignition related failures. Work this one step at a time.

 

I was only saying cause mine started small just a lil miss when warmed up than out of the blue at a stop lite started to feel like it was gana shut off anyways if it is the LIM he will find out soon Fixed mine for 50 bucks and some sore hands! car runs Great now!

 

thanks guys for all the help and advice.....
still acting up so im gonna go ahead and get my state inspection done first thing in the am so it will hopefully pass because as of now my check engine light still has not come on so I wanna get that done before it does. if I find out what it is i'll let you all know.