My wife's 97 Lumina is running REALLY rough and showing codes P0300 (random cylinder misfire) and P0442 (Evaporative Emission Control System Leak Detected (Small Leak)).

Any ideas? Any help would be greatly appreciated!

Thanks,

Jeff Bradley

Look for vacuum leaks...

The p0442 could be as simple as a loose/bad gas cap. If it's been a while since you've tuned it up (plugs, wires, pcv valve, fuel filter), any of those could cause the p0300 code. Don't believe the 100k tune-up/spark plug claims, as they are bogus.

I took it in to a mechanic and he is now pulling a THIRD code: a bad throttle position sensor.

Can anyone tell me how (or where) to check/replace the vacuum lines? I tried pushing the obvious lines together and that actually seemed to have something of an effect on how the car performed, but I don't know where else to check.

The mechanic seems to be stumped, and wants to replace a coil pack and the throttle position sensor. He admits that this may not fix anything, but wants to charge me $300 for the experiment. I haven't let him do this yet.

Any advice would be gratefully appreciated.

Jeff

Make sure the pcv valve (in the front valve cover) rattles when you shake it, isn't leaking around the grommet, and the hose isn't split or anything.

Vacuum lines all originate around the intake and spider out to various items, so I can't tell you where to look, you just gotta chase them from their origin and make sure they are intact all the way around.

You could try pulling the inlet from by the headlight to the airbox off, so you could block the inlet with your hand, and see if it tries to pick up and run right with the air partially choked off, that'd confirm the vacuum leak hypothesis.

If you get ANY reaction from it by messing with vacuum or air intake DO NOT let this "mechanic" replace any ignition parts...you'll be throwing money away.

Modules and coilpacks generally produce either no-start, stalling or distinct rhythmic misfire when bad. I don't think it has anything to do with that.

You can get a spray bottle with water and mist all around under the hood, if it is sucking air, the motor will react instantly when the water is drawn into the leak...

TPS is VERY easy to change, part is under $40. I can talk you through it yourself (if you can change a lightbulb, you can do this) two screws hold it on, one electrical connector...

The TPS on mine (also '97) went bad a couple of months ago, but it produced screaming high idle and erratic upshifts, not spastic running...

Does it run rough all the time, or only under load at speed, like going up a hill on the highway - some people call it 'bucking and Jerking' ?

hey does your car ever not start

It always seems to run rough, althouth the problem is WAY more noticeable at low (idle) RPM's. Now that we have a bad TPS code, I'm wondering if that could affect the idle speed. It seems to idle so low now that the oil light is starting to flicker. Once you get up to 40-50 MPH range the problem seems to be less of an issue, but it's still there. At low speed/RPM's the problem is more of a "shudder" than "bucking and jerking".


I replaced the PVC valve today (and broke the rubber elbow in the process, it was hard as a rock) and it seems there might be some *minor* improvement.

Thanks for the reply.

Jeff

hey i have the multiple cylinder misfire and Ive been told its not getting enough fuel pressure. Im checking it tomorrow.

I don't recall the car ever not being able to start, although it often seems like it's going to stall. Before I futzed with the vacuum lines, my wife told me that she was unable to accelerate and use the A/C at the same time. That seems somewhat better now.

Thanks for the reply,
Jeff

I don't recall the car ever not being able to start, although it often seems like it's going to stall. Before I futzed with the vacuum lines, my wife told me that she was unable to accelerate and use the A/C at the same time. That seems somewhat better now.

Thanks for the reply,
Jeff

We have this same type of problem with our 98 Luminia. I replaced the plugs, wires, all three coils, and the electonic module. The car ran like a new car. Buttttt. Its now 6 months later and everything is back again. I am not a machanic but normal logic tells me the problem lies one step further than the electonic module. Anyone know what is the next thing inline in the ignition system is?
thanks for listening
Norm