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Old 12-16-2011, 11:22 PM   #1
t100
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Default would a bad PCV valve cause this?

so I bought a Geo Prizm tonight for $400. it has the 1.6L 4A-FE engine with auto trans, 160k miles, 1995 LSi model, fuel injected, with distributor.

the problem: cold start, everything works fine, it idles, rev's and drives. once it's warmed up, it idles fine but when steps on gas, it stalls. but if I feather the gas pedal, it can rev up slowly, it's same when in neutral or in drive. once the rpm builds up, it runs ok. there's no tach on the dash. "check engine" is NOT on.

since it's late and the 9-month old is sleeping, I can't do too much in the garage. so far, I found the PCV valve is stuck open, air can go both ways.

could it be just a bad PCV? (did I get lucky with a $2 part?).

I'll do more tests tomorrow, so far that's all I got.
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Old 12-17-2011, 12:45 AM   #2
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Default Re: would a bad PCV valve cause this?

With a stuck open PCV, I'd expect to see a slight misfire at idle, symptoms similar to a vacuum leak (because it isn't regulating airflow like it should), and excessive oil consumption.

So, yes it is possible that it's the cause of your problems, but I'd still verify that there aren't other things going on in addition to the bad PCV.
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Old 12-17-2011, 06:35 AM   #3
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Default Re: would a bad PCV valve cause this?

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and excessive oil consumption..
may that lead to clogged EGR system????
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Old 12-17-2011, 07:26 AM   #4
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Default Re: would a bad PCV valve cause this?

We had a Prism that had a similar issue, start and run fine, then it had similar symptoms but would then die, after about 20 minutes it would start and run fine again. I thought it was the fuel pump and replaced it, still had the issue. We were talking to the guy at the parts store and he said he had the same issue, spent $200 to have it diagnosed and it was the ignition coil in the distributor. We replaced the coil and fixed the problem.
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Old 12-17-2011, 07:37 AM   #5
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Default Re: would a bad PCV valve cause this?

A bad PCV valve will usually cause a poor or unstable idle due to it causing an excessive vaccum leak. All pcv valves are, in addition to vaccuming out the crankcase metered vaccum leaks meaning the engine is designed to run with the proper pcv installed. I would look more towards weak spark when the engine is hot, something causing a lean condition upon acceleration(check fuel pressure or restricted injectors),Timing belt maybe jumped a tooth, coolant sensor out of wack, etc.
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Old 12-17-2011, 08:00 AM   #6
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Default Re: would a bad PCV valve cause this?

Thanks fellas.

Since it's a beater, I'm gonna start with the cheap parts, PCV, fuel/air filters, plugs. eventurely, I'll replace the timing belt, tensioner, front main seal, water pump. I checked with local parts stores, no one has Gates(only brand I trust besides OE) kits in stock. I don't know how good is the Dayco kit, it's American made.
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Old 12-17-2011, 08:14 AM   #7
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Default Re: would a bad PCV valve cause this?

A bad tip hesitation/stall is typical of a vacuum leak.

Being a 16 year old vehicle, you should also replace the PCV grommet and hose. These are also cheap fixes and frequently overlooked.

With the engine running, try spraying some carb cleaner around any gasket that seal the intake manifold and watch for RPM flairs.
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Old 12-17-2011, 09:13 AM   #8
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Default Re: would a bad PCV valve cause this?

I agree with the above guys....but on the having to feather the throttle....to keep it running? I would start looking at fuel....maybe a bad fuel pump or fuel filter?
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Old 12-17-2011, 09:37 AM   #9
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Default Re: would a bad PCV valve cause this?

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I agree with the above guys....but on the having to feather the throttle....to keep it running? I would start looking at fuel....maybe a bad fuel pump or fuel filter?
Ours did the same thing with the bad coil, that is what lead me to believe it was a fuel delivery issue.
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Old 12-17-2011, 09:44 AM   #10
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Default Re: would a bad PCV valve cause this?

It might be worth checking the fuel pressure to see if the fuel pump is weak or even the fuel filter is clogged. Just change the fuel filter first to see what that does. I rented one of those fuel pressure guages from Auto Zone for Free with a credit card one time. If it's not a fuel problem my next best guess would be the ignition coil like earlier mentioned, those do funny things once warmed up.
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Old 12-17-2011, 09:46 AM   #11
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Default Re: would a bad PCV valve cause this?

Vacuum leak or Throttle Position Sensor (TPS)
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Old 12-17-2011, 10:06 AM   #12
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Default Re: would a bad PCV valve cause this?

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the problem: cold start, everything works fine, it idles, rev's and drives. once it's warmed up, it idles fine but when steps on gas, it stalls. but if I feather the gas pedal, it can rev up slowly, it's same when in neutral or in drive. once the rpm builds up, it runs ok. there's no tach on the dash. "check engine" is NOT on.
Haven't you heard? Tachometers are useless.
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Old 12-17-2011, 10:27 AM   #13
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Default Re: would a bad PCV valve cause this?

Being a 1995 wouldnt this be an obd1 or similiar computer set up? Im not familiar with geos o I'm not sure but I think it would be worth looking into the codes a little more being an old operating system. You may find a hint that is not setting off the CEL.
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Old 12-17-2011, 06:39 PM   #14
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Default Re: would a bad PCV valve cause this?

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We were talking to the guy at the parts store and he said he had the same issue, spent $200 to have it diagnosed and it was the ignition coil in the distributor. We replaced the coil and fixed the problem.
I didn't get much time working on it as I spent most of the day baby sitting, no computer, no TV. my wife did pick up spark plugs and fuel filter I ordered.

you may hit the nail on the head, after dinner I got about 30 minutes of garage time, here is what I found out about the coil. there's a half inch crack in the epoxy filler right at the out put electrode, it doesn't look factory at all. also, there's a hole in the middle of the crack, it's the size of a paper clip wire.
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Old 12-17-2011, 07:06 PM   #15
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Default Re: would a bad PCV valve cause this?

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I didn't get much time working on it as I spent most of the day baby sitting, no computer, no TV. my wife did pick up spark plugs and fuel filter I ordered.

you may hit the nail on the head, after dinner I got about 30 minutes of garage time, here is what I found out about the coil. there's a half inch crack in the epoxy filler right at the out put electrode, it doesn't look factory at all. also, there's a hole in the middle of the crack, it's the size of a paper clip wire.
Sure looks like an issue. I didn't want you to make the same mistake I did replacing the fuel pump. It sure acted like a fuel issue but the coil fixed it.
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Old 12-17-2011, 07:32 PM   #16
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Default Re: would a bad PCV valve cause this?

Put a dab of silicon dielectric grease on the center and all side contacts on the cap plus one on the end of the rotor. Cheap peace of mind. "An ounce of prevention ..."
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Old 12-17-2011, 08:37 PM   #17
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Default Re: would a bad PCV valve cause this?

could also be the catalytic converter clogged up. Sometimes they flow better cold and when heat up they close up. That happened on a Chevette we had.
Fine when cold then hot the thing would die with no power when you tried to accelerate.
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Old 12-17-2011, 10:13 PM   #18
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Default Re: would a bad PCV valve cause this?

the other beater I bought this pass summer had the same problem but it was a dirty filthy gummed up MAF sensor. a $2 quick fix.

this one, has a MAP. and because of the bad PCV, there's oil everywhere. I took a peek at the pistons through the spark plug holes, they are pretty dirty. I'm going to pick up a new coil and a can of Seafoam tomorrow morning, see how they work.

drive belts and valve cover gasket will be next, that will be the time to check on if there's a sludge problem. it's a beater project, I'm trying to spend as little money on it as possible.

I pulled the O2 sensor tonight and it looks rough. I know Toyota's are always picky on the O2, I don't want to buy a $55 Denso unless I have to.

the car also has some front end damage, time for me to try on hammer and dolly.
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Old 12-18-2011, 07:12 AM   #19
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Default Re: would a bad PCV valve cause this?

I have a funny story about the Prizm we had. We always de-badge our cars, it's just that thing we do to personalize them. We also typically give the cars a name, something will always come up that just fits. So we have the GEO, and Prizm badges off sitting on the bench and my wife walks by and says "you should call it the Giszm", my son and I about fell over laughing and the name stuck. To top it off we took the G from the GEO badge, and the izm from the Prizm badge, put them together, and re-installed the badge right over the trunk lock.
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