98 Lumina Rough Idle

I’ve got a rough idle on my 98 lumina. My father recommended I try fuel injector cleaner, which I did, but so far no change (how long should it take for this to clear stuff out anyways?) Since that didn’t work, I’ve also tried cleaning out my EGR (Wasn’t that bad) and also the end/tip of my IAC valve (this was pretty bad).

After buttoning everything up I took it for a drive, noticed I still had a pretty rough idle. It’s not awful, more so irritating, and it does cause the interior of my car to shake.

Any further suggestions?

Well…there are a hundred or more things that could cause your engine to have a rough idle. You would be in the poorhouse before you tried everything to correct it. What you need is a good independent mechanic to check your engine and eliminate all the possibilities. It could be something as simple as bad gas or something far more expensive like low compression.

Post the computer’s diagnostic codes, both active and pending. That’s a good place to start.

This could be as simple as a fouled plug, or one that has no electrode left anymore.

Have you @Ptohara gotten the codes read.
Most auto p[arts stores will do this for free and many will give you a print out of the codes.

Before you take their recommendations on replacing parts, list the codes here so we can make some suggestions.


Pull the plugs and take a look at them or replace them if they have a lot of miles on them and replace the wires too.

Thanks for all the feedback guys. First, let me say that the idle isn’t as rough as you might think. This is why I’m not in panic mode over it. Also, since I’m between jobs (I’m starting a new one in a few weeks) I’m extremely bored. Since I’m learning cars I’d like to try a few more things.

Re: error codes. Let me give you a brief history. This car had a rotted out gas tank (3 months ago, maybe). I overpaid some chain place to replace it, and they also changed out the fuel pump (my understanding is it’s a good idea to change both, since you’re already down there and all). So I pick up my car, notice it has a check engine light. No big deal, probably my old EGR code, damn thing’s probably stuck up with carbon again. Take it to Advanced Auto. No EGR code, but cleaned it out just to be sure. The code I have in the OBD II now is a P0452, which has to do with pressure int he gas tank. I’ve already replaced my gas cap, still have the light.

I can go today to get codes read again, but if I only have the PO452 I’m not sure how that relates to a rough idle. Besides I think the rough idle has been going on longer than my tank issue.

But what do I know I’m not a mechanic.

OP here. I’ve returned from my adventures.

I now have 3 trouble codes (a record!). Let’s start with the one I’ve already mentioned, the PO452, the one that started after my new fuel tank and fuel pump and lines were installed.

Next, there is P0440 and PO141. Never had these before.

A few other symptoms that might be note worthy. When I open up my gas tank by removing the cap, it often makes a sound, similar to when you take the top off of a 20oz of soda. In other words, it sounds like there is too much pressure in the tank.

Another thing I’ve noticed is that the exhaust (muffler) seems to be “popping”. This is most noticeable when I’ve stopped and turned the car off. It is a slow pop, possibly once every few seconds until it completely dies off. I only mention it because in the years I’ve driven this beast I’ve never heard it. Oh, and while I did smell an immense amount of fuel fumes before I got my new tank, I don’t smell anything now. Never.

Aside from all of this, I haven’t noticed a serious reduction in gas mileage. The car seems to run great. Even with a rough idle it never stalls or hesitates.

Things I’ve done recently: Cleaned out EGR valve, cleaned off IAC valve. Changed oil/filter. Checked engine air filter (not bad enough to be concerned).

Where the hell do I begin?


P0141 heater circuit oxygen sensor bank 1 sensor 2 . . . that’s a downstream sensor, after the cat. I’ll bet you lunch the heater circuit has failed, and you need to replace that sensor

P0440 evap system small leak. Could be something so simple as a rotten fuel cap seal or a bad hose

p0452 fuel tank pressure sensor circuit low voltage. Make sure it’s plugged in correctly. Make sure the wiring isn’t pinched

Everything you’ve done so far has absolutely nothing to do with any of your fault codes

Please note that everything I’ve done I’ve either needed to do or thought it was going to help with the rough idle.

P0141 - this one seems the easiest. Fun little beginner’s project for me to spend an afternoon cursing over.

P0440 - Fuel cap is brand new, so I’m looking at a bad hose? Sounds fun.

p0452 - This being the one that I got just after my new tank, fuel pump, and delivery were installed. I wonder if they goofed on the install. Either way, the shop that did this is now a 6+ hour drive away, and correct me if I’m wrong but checking the wiring here would likely involve removing the gas tank, right?


“so I’m looking at a bad hose?”

you need a shop to use their evap/smoke machine to determine IF you have a leak. And if so, where is it located. And then give you a quote to repair the problem

I put if in parentheses because there are cases in which you can have an evap leak code, when in fact there is no leak. That’s where diagnosis comes in

As far as checking the wiring goes, you might be able to access some of the wires without dropping the tank. Never worked on a 1998 Chevy Lumina, so I literally wouldn’t know

here’s a question . . . do you live in an area that has emissions inspections?

If not, you could ignore those fault codes. Because fixing those problems is not going to get your car running any better

I live in Michigan and we do not have inspections. I’m also gathering that these fault codes are not the reason why my engine is idling rough. I’ve been told I need to check the wires and plugs, so I’ll do that next before getting my father involved.

Thanks to everyone for the advice. I’ll follow up once the idle is taken care of.


You got it . . . those fault codes have absolutely nothing to with the way the engine is running

Since Michigan doesn’t have inspections, if I were in your shoes, I would not worry about those fault codes . . . unless you’re planning to move to a state that does have smog inspections

Please let us know if the ignition tune up helped

By the way, if you get your dad involved, would that mean that he sits down with a 6 pack, and bosses you around, while you roll around under the car . . . ?


These are all emissions related.

P0141 heater circuit oxygen sensor bank 1 sensor 2 . . .

The computer monitors a sensor before the cat and a sensor after the cat, the purpose is to see if the cat is doing its thing or not. If both sensors read the same, then the computer knows the cat is doing nothing, it’s acting like an empty pipe, so it needs fixing. The post cat sensor won’t work though until it reaches a certain temperature, which is a pretty hot temperature. That’s too much waiting around & possibly spewing out a lot of pollution until the sensor operating temperature is reached for the EPA, so the car manufacturer is required to use a sensor with a quick-heating coil inside. Then the battery current heats it up fast, not the exhaust gas. The heater is just a coil of wire, and requires a lot of current, so the most likely causes are a failed (broken wire) coil inside the sensor, blown fuse for that circuit, or corroded connector.

P0440 evap system small leak.

As fuel is used as you drive the car, air has to be let into the tank to replace the vacated space that used to be occupied by the fuel. Some method has to be incorporated into the fuel tank vent system to allow air to come in, but not go back out, b/c the air space above the tank contains a lot of fuel vapor in it, and if that escapes into the atmosphere, it pollutes the air we breath. So the EPA requires the car manufacturer to incorporate a test that the computer does on occasion to see if that system is working or not. It either pressurizes or puts a vacuum on that air space, and measures to see if that pressure holds or not. This code is saying yours isn’t holding like it should, it is leaking a little. It is supposed to be air tight, but yours isn’t.

p0452 fuel tank pressure sensor circuit low voltage.

This is the sensor mentioned above, which measures the pressure in the air space above the fuel during the computer test of the fuel ventilation system. It is probably related to the code above. For example, if that sensor was on the fritz, the computer might think there was a small leak, when in fact there isn’t, b/c it is the sensor that isn’t working.

Rough idling … It is possible the last two codes are related to the rough idling. Part of the fuel tank air ventilation management (called the evap system usually) is that fuel vapor is stored in a canister, and that canister has to be emptied from time to time. The way it works is the canister fumes are – at certain times decided by the computer – sent to the engine, to be burned. If too much or too little fuel gets drawn into the engine, that could confuse the computer and cause rough idling. The other possibility for a rough idle is that not enough air is being drawn into the air space above the tank as the fuel is used, and that is forming a vacuum in the tank, and preventing enough gasoline from leaving the tank.

The problem with trying to solve a rough idle on a car this age is that the possibilities are numerous. Just to lost a few:

  • the compression may be uneven due to wear and/or associated factors like burned or sticky valves, or even tired valve springs.

  • the EGR system … but I see you’ve done that dance already.

  • you could have a weak coil in the coil pack.

  • if this '98 has a distributor-based ignition system, the distributor shaft or its associated parts could be worn to where it’s loose either laterally (sideways) or axially (up & down), making the ignition timing erratic.

  • The Idle Air Control (IAC) system could be dirty. But you’ve already addressed that.

  • you could have a simple vacuum leak.

If it were mine, I’d probably hook a vacuum gage up and see it the needle is stable. If it isn’t suspect a vacuum leak or a valve problem.
It wouldn’t hurt to take the compression readings too.

Even though you’ve changed the fuel pump, you might want to check the pressure. The crud that was in the rotted tank may have gotten into the supply line. In all honesty, the shop that sent you home with a CEL after changing the tank and pump should not have.

@the same mountainbike, it’s likely that after installing the new tank, pump, and delivery lines, there wasn’t a CEL. I honestly should have walked right back into the shop but I was in a hurry and just assumed it was the reoccuring EGR error.

It’s likely I’ll just wait until my father can sit with his whiskey on ice and direct me on what to try next.


“my father can sit with his whiskey on ice . . .”

your dad has better taste than mine did . . .


The evap leak could be as simple as an old O-ring that did not seal properly when they replaced the tank. A leaky charcoal canister also is common with the age of this car.

A smoke machine should show the problem right away, but sometimes it’s hard to see that little whiff of smoke.

This could correct all of your PO4xx codes.

Get the rough idle fixed and it then you can chase these other codes.

1st. thing to consider is to take a real good look at all the vacuum lines. Any cracked or loose line could affect the vacuum enough to give you a rough idle. The rubber/plastic lines dry out after years exposed to the heat from the engine, and can easily leak.

2nd, put new plugs, a distributor cap with rotor, and wires on it if that has not been done recently.


Vacuum lines, eh? ::rubs chin:: I shall return.

(Also for the record my father and I did spark plugs and wires back in late 2013/ early 2014. While it’s been driven a lot since then I think the plugs are the cause of this rough idle).