shuddering regal, rough idle

[david95]

I have a 95 Buick Regal, V6 3.8 Liter. The symptoms are the following: stuttering idle. And lack of response at times when I try to accelerate. Like sometimes I’ll be driving on the highway, and having no problems. Then I’ll be going up a hill at around 55 mph, and then the car will shudder as I try to maintain a speed of 55 mph. So I have to ease off the accelerator and slow down. At first I thought this was a transmission problem, but I’m guessing it’s the same problem that causes my choppy idle.
So I had this acceleration problem on the highway when I was going up a hill. And a weak idle. These problems have been going on for several months now. They were annoying, but didn’t seem that serious. Then all of a sudden, on a rainy day, the car was really responding poorly to acceleration at all speeds. I was able to drive around, but I couldn’t count on the car responding right away when I hit the gas pedal. And the car would shudder at times.
Then, I didn’t drive the car for a few days, and then it was dry, no rain, and the car ran better. So I’m thinking humidity makes the problem worse.
I have also noticed over the past few months, that the car runs best when I start it up after a few days of not running it. Then if I drive the car a few miles and let it sit for about 2 hours or so, it would idle weakly when I would start it up again. The car’s been doing that for several months now, but it wasn’t really affecting the drivability or the response of the car when I hit the gas pedal.
Now it’s gotten much worse. So, I’ve already replaced the following items myself to no avail: mass air flow sensor, oxygen sensor, and egr valve. I’m guessing the next thing to fix is the pcv valve. But I also think it might be the fuel pump. My first guess though is the pcv valve.
What else could it be? And is there any easy way to test to see if the fuel pump is going bad? Or should I just take out the pcv valve and see if it looks bad?

[maxwedge]

Welcome to AF. There is no quick diagnosis for this, from here your description sounds like an engine misfire, how old are the plugs and wires? Any cel? have you scanned it for misfire codes? You are just throwing parts at this with no idea of where you are. Test fuel pressure also.

[david95]

Originally Posted by maxwedge

Welcome to AF. There is no quick diagnosis for this, from here your description sounds like an engine misfire, how old are the plugs and wires? Any cel? have you scanned it for misfire codes? You are just throwing parts at this with no idea of where you are. Test fuel pressure also.

Thanks for the post maxthread. Unfortunately you are right, I am just throwing parts at the car. I'm not getting a check engine light, and I put new spark plugs in 10k miles ago. The wires were checked at that time and were supposedly ok. So I'm thinking it's not the plugs or the wires.
I'll get the fuel pressure tested though, that's a good idea. Is there an easy way to test the fuel pressure, or do I have to take it to a shop to get tested?

[richtazz]

David,

If you do a lot of work on your own cars, a fuel pressure tester would be a wise investment. You can get a decent one from Actron for around $30-$35 and they are a nice unit. One diagnostic fee at a garage would cost as much or more.

[enslow]

1) check the coils.
2) either replace the wires or reseat them all and use dielectric grease in all boots (at the coils too).

It's also a wise investement to get yourself a good scantool. I like the AutoXray, but I'm sure there are others that don't cost too much ($3-500 instead of thousands). Beware though, some cheaper scantools don't sample data frequently enough to be very useful.

[david95]

Originally Posted by richtazz

David,

If you do a lot of work on your own cars, a fuel pressure tester would be a wise investment. You can get a decent one from Actron for around $30-$35 and they are a nice unit. One diagnostic fee at a garage would cost as much or more.

Thanks for the idea richtazz. What do I connect the fuel pressure tester to? Does the car need to be running when I test it? Thanks for your help. This problem has got me seriously confused and frustrated.

[david95]

Originally Posted by enslow

1) check the coils.
2) either replace the wires or reseat them all and use dielectric grease in all boots (at the coils too).

It's also a wise investement to get yourself a good scantool. I like the AutoXray, but I'm sure there are others that don't cost too much ($3-500 instead of thousands). Beware though, some cheaper scantools don't sample data frequently enough to be very useful.

Thanks enslow for the reply. I must admit I'm a bit confused, dumb, or slow, but what do you mean by "check the coils". Is that the distributor? And what kind of tool do I need to check the coils? I'm trying to do as much of the work as I can by myself, and I don't mind getting the right tools, but I haven't done any work on spark plugs or wires before, so I probably don't know the proper terminology.

[enslow]

As far as I know, a 95 Regal doesn't have a distributor. The spark timing is determined by the computer.

If you look at the plugs, you will see wires that go to three "black boxes" bolted to the side of the engine. These are the coils. You can buy a coil tester from KMS tools or similar stores that sell automotive tools. It comes with instructions. Sometimes a coil can be intermittent, though. If you know some one with a 3.8, you could try swapping coils and see if that fixes your problem.

Wires are cheap, so I'd replace them anyway. I usually stay with GM wires, they seem pretty good. Just make sure they follow the same routing as the old ones you remove. I usually do one at a time so I guarrantee the go on the way the came off.

There are other causes for your symptoms, but I consider plugs AND wires to be part of a regular maintainance thing. If you get your hands on a good scantool, you can determine what plug is misfiring. Then you can move coils around and see if the missfire moves to a new cylinder. If so, then it's your coil.

[david95]

Originally Posted by enslow

As far as I know, a 95 Regal doesn't have a distributor. The spark timing is determined by the computer.

If you look at the plugs, you will see wires that go to three "black boxes" bolted to the side of the engine. These are the coils. You can buy a coil tester from KMS tools or similar stores that sell automotive tools. It comes with instructions. Sometimes a coil can be intermittent, though. If you know some one with a 3.8, you could try swapping coils and see if that fixes your problem.

Wires are cheap, so I'd replace them anyway. I usually stay with GM wires, they seem pretty good. Just make sure they follow the same routing as the old ones you remove. I usually do one at a time so I guarrantee the go on the way the came off.

There are other causes for your symptoms, but I consider plugs AND wires to be part of a regular maintainance thing. If you get your hands on a good scantool, you can determine what plug is misfiring. Then you can move coils around and see if the missfire moves to a new cylinder. If so, then it's your coil.

enslow, you're correct. The 95 Regal, 3800 V6 doesn't have a distributor. I'll check the coils next to see if they are the problem after I take a look at the PCV valve.

Right now, I'm trying to check the PCV valve. However, my manual is leading me to the wrong spot. It was telling me the PCV valve was under the MAP sensor. But I think the PCV valve is to the left of the engine, and to the right of the alternator. There's a cylindrical thing attached to the engine with "PCV" written in two places on top. That seems to be a pretty obvious indicator that it's the PCV valve.

So assuming that's the PCV valve, but unfortunately I'm still stuck. I'm trying to get the PCV valve off, and I can't figure out how to do it. I'm guessing I have to push down and turn it counter-clockwise, but I can't get any force on it. Is there a special tool you need to remove the PCV valve? What makes it tough is I have some wiring running right on top of the PCV valve, and I have to use one hand to hold the wiring out of the way, which only leaves me one hand to try to rotate the PCV valve.

[enslow]

Mine was pretty tough to get off at first also. Basically yeah, push and turn. Good luck! Mine is on the front side and easy to get at. :P

[richtazz]

use a bungee cord to hold the wiring out of the way (ghetto, but it works) then as enslow said, it's just push and turn. The PCV valve is under the MAP on Vin-K 3800's, not on the Vin-L engine in your car, so your repair manual is incorrect.

As far as where to check the fuel pressure, there is a schrader valve with a black cap on it near the fuel pressure regulator, this is where you attach the fuel pressure gauge. Check the pressure with the key on/engine off first (should be 41-44 psi), then start the engine and it should drop 3-7 psi. With the engine still running, pull the vacuum hose off the regulator and the readings should jump back up to near key on/engine off readings.

[enslow]

Originally Posted by richtazz

...
As far as where to check the fuel pressure, there is a schrader valve with a black cap on it near the fuel pressure regulator, this is where you attach the fuel pressure gauge. Check the pressure with the key on/engine off first (should be 41-44 psi), then start the engine and it should drop 3-7 psi. With the engine still running, pull the vacuum hose off the regulator and the readings should jump back up to near key on/engine off readings.

One further test with the fuel pressure test: Goose the throttle a little while watching the fuel pressure. It should not drop.

[david95]

Well, I was finally able to get the PCV valve cover off. I used the two prongs of a wrench to push into the grooves of the PCV valve cover, and then I was able to get enough leverage to twist it counter-clockwise. It only cost $3 for the new PCV valve. The clerk at the auto parts shop said they're supposed to replace the PCV valve with every oil change. However, I doubt it's ever been replaced. I'm not sure what imaginary repair shop he's talking about when he says they should change the PCV valve with the oil change.
Anyway, I noticed the old PCV valve was coated in oil, and the ring had slid down halfway on the bottom part of the PCV valve. That may have happened when I removed it. I could shake the old PCV valve and it rattled, so I don't think it had stopped functioning altogether.
I installed the new PCV valve, and then started up the Buick. I hadn't started the car in over a week, so it sounded a bit choppy and unsteady at first. but then the engine smoothed out, and it sounded much better than the last time I started it. There still is an occasional lull or break in the engine idling, like a spark plug is missing. But it is improved.
However, it was a clear, dry, cool day in Austin, about 50 degrees. I'll have to try the Buick again when it's raining, because that's when the engine has responded horribly in the past. I think there's an improvement, but I'll give it another try soon and make sure. There still is something else going on though, and I suppose I'll check the coils, plugs, and wires next. But I'm optimistic that the new PCV valve actually improved the engine situation.
I'll post again soon when I've started it up again.

[david95]

Hey, richtazz and enslow, thanks for the tips on how to check the fuel pressure. I'll definitely check that too. I'll probably do it this coming weekend. I'm getting run ragged at work this week and I'm guessing next weekend will be my next chance with some free time.
For some reason, I don't think it's a fuel pump problem, but of course I could be wrong. It's the fact that the engine runs differently based on the humidity (i.e., runs good in dry air, runs terribly in the rain) and that it runs best when I haven't started it in over 12 hours vs. runs poorly when I've driven it 2 or 3 hours prior and then start it up again.
I'm not sure what to make of those clues, but that makes me think it's something with the engine, fuel injection, plugs, wires, or anything that would change based on moisture in the engine, in the oil...?? Frankly, I've got a bunch of guesses but haven't found the solution yet. But I definitely feel like I'm getting closer. And thanks so much for your help, richtazz and enslow, sometimes I get stumped and frustrated and it's good to get some feedback on what to try.

[david95]

I still have the shuddering, non-responsive problem. I started the car this morning, and it sounded fine at first, and so I took it for a drive. Then as I was stopped at a red light, the engine started misfiring and the RPM meter was jumping up and down as I sat waiting at the red light. Then the car stopped responding normally when I pressed on the accelerator. I could still get around, and the car didn't stall on me, but the engine was clearly not functioning normally.
I guess the next thing I'll check is the fuel pressure. I'm starting to think it could be a fuel pressure problem after all. The engine problems today had nothing to do with humidity or rain.
I'll go to the auto parts store on saturday and get a fuel pressure gauge. I'll post back with the results.