1998 LTZ Sputters While Driving

I could use some help here. I have a 1998 LTZ 3.8L (97K) that is sputtering when I am driving down the road.
Here is the skinny:
Tach begins to jump around erratically
Periodically occurs (there is no specific RPM at which this happens)
Usually occurs when driving on level ground at constant speed
If I drop off the gas it stops for a little bit, but usually begins again when I give it gas.
If I give it gas, the sputtering (stalling, coughing, etc) gets worse until it downshifts, then I let off the gas, it upshifts and is better for a bit, but usually will begin occurring again.
This problem seems to come and go: I just made a 300 mile trip and it only happened once, but the last time I made the same trip, it was happening almost the entire way.

It is not spitting any engine codes and I have not had the fuel pressure tested yet.

When I removed the engine cover plate (the plastic molded shield with 3800 emblazoned on it), the fuel feed line behind the engine seems to be loose (I press down while the system is pressurized and it began to leak). This is the rubber line that plugs into the aluminum fuel railing.

Could these two problems be related? Any help would be appreciated.

:edit:
I found the following post (http://www.automotiveforums.com/vbulletin/showthread.php?t=603840) but no solution ever came from it.
I heard that ign control module could be culprit, but again, no one ever came back to tell a success story...

Welcome to AF. First how old are and what type of plugs, this can be caused by many things, bad plug, coil, wires bad or dirty injectors and so on, it should be scanned to to look at misfire counts when this occurs of all the tune up issues are up to date. How much does the tach jump this could indicate a crank sensor or ign module also.

Wow, that was a fast reply. Thank you for the welcome.

I just put new Bosch wires and plat's in about 4k miles ago. The injectors are original (so 97K on them) but I would ass.u.me that if it were injectors, the power probs would be at least slightly consistent. I get a good, clean, power curve all the way up to red-line during acceleration.

The tach is jumping from 500-1k RPM. The issue occurs anywhere from +/-20mph to 85mph (perhaps more, but I prefer not to test the theory).

Doesn't the crank sensor spit a code when it fails? My '01 Sierra 2500 did (on both the crank and the cam sensors) but maybe the '98s didn't.

That may not set a code on a 98 car, as the newer obd11 systems do, this can be a problem finding this, if you had a scanner set up you could look at the tach signal and see if it drops out completely when this occurs pointing to a cps, or possible icm, tough diagnosis here. I do not like the Bosch plugs at all here, oe Delcos are almost a must, but usually the rpm drop out would not be as severe and you only have 4k on them, but they do not work in GM 6 cylinder engines. Also look for pending codes if you can get a good scanner on it.

Has the sputtering started since the plugs/wires were replaced?

Don't like the Bosch's, eh? I have traditionally had pretty good luck with them but plugs are cheap and I don't mind trying another brand. The only part I hate is getting to the one behind the engine, driver's side.

I watched the tach a little closer tonight and have to modify my symptoms... the tach is only dropping 100-500 RPM's. Sorry.

The problem began quite a while ago, while I was traveling from Las Vegas to Reno (in the middle of summer +/-115F, +/- 500miles). That was about 10k miles ago. I have been trying to figure out what the problem is since. I usually do the repairs on my vehicles.

I thought that I had narrowed it down to the pump or the regulator, but I wasn't able to get my hands on a pressure tester yet. I am hoping that I will be able to get my hands on one tomorrow or Friday. Service manual I read says that fuel pressure should be between 48-55psi and should drop 3-10psi at operating temp idle but should stay in the limits (so I don't know how it possibly could drop 10psi and still be in the zone, but whatever).

Electrical circuits to the fuel pump all check out. I had stopped by Autozone and had them use their analyzer which reported all was well (no codes).

Maxwedge, are you suggesting that I test with the tester while driving (as safely as possible, of course) when the sputter begins happening? I had not thought of that...

Again, my problem seems identical to the post that I linked to earlier. I was hoping that GW84 would have posted an update, but no luck. I'll stop by the store tomorrow and change out the plugs and wires. This weekend, I was planning on pulling the injectors, cleaning them in a solvent bath and replacing the o-rings and fuel filter.

Other than that, I am stuck...

hey man, I was just reading your post. Obviously you know I've had a similar problem on my '99. I've had it hooked up to a scanner and it showed no problems except for an O2 sensor going/gone bad. I haven't done anything to it yet. I changed my oil about a month ago and haven't had the jerking problem since. (I'm not sure if an oil change would fix the problem, but the car is running fine now).
If you haven't read my other threads on the topic, a friend of mine has a '96 (3.1L) lumina that does the same thing. His has a newer transmission in it, so I don't know if that could be a factor.
Good luck! Let's keep each other posted and if we figure something out maybe we can spread the word.

Oh well. I was hoping that you would have the magic bullet for the problem. Thank you for the reply, gw84.

have you had this vehicle since it was new?

man, i'd say start with the basics, get the fuel leak fixed. Then go from there.

The fuel leak was an easy fix,though, I did have to call the dealership to get a p/n for the fuel line. Stupid line (from sender to railing) was $53. That was the first thing that I fixed a few days ago. The last thing that I want is my engine compartment to catch fire...

The problem is still present, but I do have a new plan of attack. While at the stealership, I had the s.m. take a look at the car (I guess for a $53 piece of rubber, they will look at your car for free). He thought it was either the ICM or one of the coils. He wanted $400 to test them. I called Autozone and if I pull them off, they will test them for free (both the ICM and the coils).

I will post an update when I find anything.

OK guys, here's the latest:

No change in the sputtering.
Changed the following:
Oil
removed oil pan and cleaned (major PITA - won't do that again...)
Transfer case fluid
AC Delco iridium plugs
AC Delco wires
tore off throttle body and cleaned
pulled injectors, replaced rings and had machine cleaned
removed intake manifold and cleaned
backflushed cooling system
changed tranny fluid
installed new PCV (kit)

I drove from Reno to Vegas and back. I got 28.4mpg down and back! Mechanic down there suggested one of four things:
Cam sensor
Crank sensor
ICM
Vapor Cannister

I had the ICM and all 3 coils tested and they were all fine. It may be the vapor cannister (or associated parts). A few more tests and a few more opinions and we will see. For the $70, I may just replace the cam and crank sensor.

I'll keep y'all posted.

OK, the problem is fixed!

I changed out the vapor canister filter ($2), vapor canister purge solenoid (Delco #PT250) ($16), and vapor canister purge valve (Delco #214567) ($18). I just got back from a 400-mile round trip (and much city driving) and have not had one cough.

If it comes back, I'll post back and admit defeat with my current fixes.

Success!! (I wish I were standing on an aircraft carrier right now :)

have you had this vehicle since it was new?

No, my (now) wife bought it with 4k miles on it back in early '99.

alright! I'm glad to hear your problem was resolved! And fairly cheap, I must say. There are several AF members who will be glad to hear it! thanks again and keep us posted on any updates. GW

This may be an incredibly stupid question. But... how similar are 1998 LTZ and a 2000 Monte Carlo SS? The reason I ask is because this problem you're decribing sounds like an issue I have been having with my car. It's "surging". I have had the cylenoids (?) tested, the plugs replaced, the air filters replaced, the transmission fluid replaced, and a MUTLTITUDE of things done. Nothing works. There is no rhyme or reason to it and nothing seems to make it stop, other than downshifting (it's an automatic... I assume all SS' are) when it starts to act funny. There have been about 4 diagnostics run on it and the only code it throws has to do with the thermostat. I was told by one mechanic that his wife's car-- a 2000/2001 pontiac grandprix (I think, maybe grand am)-- did the EXACT same thing and no one could ever figure it out. My car now has 106k but started doing this somewhere around 80k.

Also, there has recently developed a "humming" sound coming from, I assume, my tires. The tires are new, and do not need air. WHAT is that all about?

Thanks for any information anyone can give me.

what size engine do you have in the monte? I'm wondering if they have the same engine and transmission. The '98 and '99 lumina LTZ's have the 3800 engine and I believe a 4t65e transmission.
Did you have the transmission flushed and a new filter installed? I've heard that having a transmission flush has been a possible culprit in these sputtering cars.

I have since sold the car to my niece and she has had no problems with the surging. I truly believe it was the vapor canistor (and associated parts).

From what I remember, the Monte is just a 2-door ver. of the Lumina (at least, back then). We'll have to wait to hear back from Jen, but I am assuming that she has the 3.8 (SS).

With the humming, I would have to hear it, but it could be one of the following:
New tires breaking in
Just different tires - some tires will have more road noise than others
Wheel bearings

If the 'humm' does not sound like road noise, then I would have your bearings checked. Unfortunately, even though they are sealed, they can still go dry. The problem with that is you can't just have them re-packed. The whole assembly has to be replaced.

Before you freak out (replacing those assemblies is very expensive), I would really be sure that what you are hearing is not just road noise from the new tires. Remember, the biggest thing that these cars (the Lumina and Monte) got nailed on by Consumer Reports was the road noise levels in the cabin. These cars are much more sensitive to new tire noise than many other cars.

I have the 3.8. I have no idea on the transmission... and don't know where to look....
The transmission fluid and gasket(s) have been replaced, as well as a complete tune up. I've had this car hooked up to a diagnostic machine 4 times and it never threw a code. I took it to a transmission guy, who hooked it up twice and nothing.

I talked to a friend of mine and he told me the tire noise could be caused by "cupping", and that I might need new shocks/struts... It is defiantly not road noise. And unfortunately, it has gotten louder.

Thanks for any help.

I would get the car on a lift put in in gear and listen closely to the front hubs for any bearing noise, compare lt to rt, also check for play in the bearing, std procedure for the basic wheel bearing analysis.

I should probably also mention that the humming in the tires completely stops when I turn right, and quiets down considerably when I turn left. When I am going straight, its sounds like I have mud tires on my car!!!