Help me figure out my car problems
December 31, 2009 1:03 PM Subscribe
Help me figure out what is wrong with my car.
OK, my car died a couple of times in the last couple of weeks, and the mechanics have so far been unable to recreate the problem, so I am turning to you to see if you can help me to diagnose the problem.
Car is a 2001 Saturn SL 4 door sedan, automatic, with about 108K miles.
When it broke down: Both times the symptoms were the same. I came to a stop, and the RPM gauge went all the way down to 0, than back up to 1000, than down, than up, and so on, up and down about 2 times a second, until it died about 5 seconds later. Starting it again, it did the same thing.
The first time, I started it, gave it a lot of gas, and pushed through the intersection. It seemed to be fine after that.
The second time, I noticed before I stopped that the car felt to be pulling and pushing slightly (this was at about 20mph), but it was very slight. After it stalled, I started it, gave it plenty of gas, and pushed through the intersection, but at this point the pushing and pulling feel was greater than before, and when I came to the next stop, it stalled again. I started it a couple of times, and pushed through to a parking spot. When it stalled again, I thought I would try to start it and give it a lot of gas (RPM's at about 4000), and left it like that for about 10 seconds. After that, the car didn't stall, and seemed to run OK, but I had it towed to a mechanic, just in case.
Other possible clues: Over the last few weeks the RPM's go up pretty high when starting the car, and also when putting it into park after driving (they used to just go up or down a little around 1000, but now when I put it into park they are jumping up to about 2500 for a couple of seconds before going back down). Also, when I come to stops, the RPMs sometimes seem to dip down fairly low before coming back up, to the point where I wondered a few times if it was going to die.
The mechanics did clean out the throttle body plate (I believe that is what they said), because that was their best guess, but if someone out there knows better or has a suggestion as to what else it might be, I would love to hear it, so that if it dies again, I will have a suggestion to give my mechanic. Alternately, if you think that the mechanics were correct, please also let me know that as well. Thanks!
OK, my car died a couple of times in the last couple of weeks, and the mechanics have so far been unable to recreate the problem, so I am turning to you to see if you can help me to diagnose the problem.
Car is a 2001 Saturn SL 4 door sedan, automatic, with about 108K miles.
When it broke down: Both times the symptoms were the same. I came to a stop, and the RPM gauge went all the way down to 0, than back up to 1000, than down, than up, and so on, up and down about 2 times a second, until it died about 5 seconds later. Starting it again, it did the same thing.
The first time, I started it, gave it a lot of gas, and pushed through the intersection. It seemed to be fine after that.
The second time, I noticed before I stopped that the car felt to be pulling and pushing slightly (this was at about 20mph), but it was very slight. After it stalled, I started it, gave it plenty of gas, and pushed through the intersection, but at this point the pushing and pulling feel was greater than before, and when I came to the next stop, it stalled again. I started it a couple of times, and pushed through to a parking spot. When it stalled again, I thought I would try to start it and give it a lot of gas (RPM's at about 4000), and left it like that for about 10 seconds. After that, the car didn't stall, and seemed to run OK, but I had it towed to a mechanic, just in case.
Other possible clues: Over the last few weeks the RPM's go up pretty high when starting the car, and also when putting it into park after driving (they used to just go up or down a little around 1000, but now when I put it into park they are jumping up to about 2500 for a couple of seconds before going back down). Also, when I come to stops, the RPMs sometimes seem to dip down fairly low before coming back up, to the point where I wondered a few times if it was going to die.
The mechanics did clean out the throttle body plate (I believe that is what they said), because that was their best guess, but if someone out there knows better or has a suggestion as to what else it might be, I would love to hear it, so that if it dies again, I will have a suggestion to give my mechanic. Alternately, if you think that the mechanics were correct, please also let me know that as well. Thanks!
It is giving all the symptoms of poor idle speed control. Now, this may be because something in the idle control is failing (unable to accurately ascertain the idle speed) or something else is causing a variation in idle speed that the system is unable to correct for before the car stalls.
The first aspect could be throttle body related (as seems to be assumed from your mechanic's reaction) but is also (the second element) likely to be fuel delivery related or from a faulty sensor. Clogged fuel filter, or dirt in the tank washing up against the pick up, could cause this problem, but so could a number of other things, unfortunately.
I very much doubt it is transmission related.
My initial investigations would be aimed squarely at fuel supply, and a clogged (or internally collapsing, perhaps) fuel filter as my first check point. After that I'd check the pump, pressure relief valve and move on to injectors after that. Next step would most likely be from dodgy/failing sensors, but I'd expect to see a check engine light and some fault codes first before that was too likely.
It's pretty hard, beyond that, to diagnose the car without getting hands on and tinkering with things, though.
posted by Brockles at 2:22 PM on December 31, 2009
The first aspect could be throttle body related (as seems to be assumed from your mechanic's reaction) but is also (the second element) likely to be fuel delivery related or from a faulty sensor. Clogged fuel filter, or dirt in the tank washing up against the pick up, could cause this problem, but so could a number of other things, unfortunately.
I very much doubt it is transmission related.
My initial investigations would be aimed squarely at fuel supply, and a clogged (or internally collapsing, perhaps) fuel filter as my first check point. After that I'd check the pump, pressure relief valve and move on to injectors after that. Next step would most likely be from dodgy/failing sensors, but I'd expect to see a check engine light and some fault codes first before that was too likely.
It's pretty hard, beyond that, to diagnose the car without getting hands on and tinkering with things, though.
posted by Brockles at 2:22 PM on December 31, 2009
I don't think that those had electronic throttle control, so it could be an IAC (Idle Air Control) valve. It would set an idle control code first. If there are no codes, it could be the crank sensor getting flakey.
posted by rfs at 2:48 PM on December 31, 2009
posted by rfs at 2:48 PM on December 31, 2009
I've experienced very similar problems in a '95 blazer. Mechanics couldn't figure out what was wrong with it...the dealership finally decided to try to replace the fuel pump...and sure enough...it was fixed.
I've had many fuel pumps die on me before, and usually they just stone-cold die....no more starting the engine at all. but this one time it did exactly as you describe...pull to a stop, and the engine revs and stalls several times.
Replaced 6 fuel pumps in my blazer over as many years. good riddance. :)
posted by AltReality at 4:36 PM on December 31, 2009
I've had many fuel pumps die on me before, and usually they just stone-cold die....no more starting the engine at all. but this one time it did exactly as you describe...pull to a stop, and the engine revs and stalls several times.
Replaced 6 fuel pumps in my blazer over as many years. good riddance. :)
posted by AltReality at 4:36 PM on December 31, 2009
Is your check engine light on?
If there were fault codes (like P0505 or P0506, for instance) for the IAC (idle air control) valve stored, a quick and cheap fix is to clean the throttle body. It's pretty common for carbon and gunk to foul up the throttle body and cause poor idle. Basically, the throttle itself is a valve that controls the flow of air into the motor when you press the accelerator pedal. When the car is stopped and the throttle is closed, the engine needs a minimum air supply to maintain an idle. The IAC is a computer controlled valve that allows air to bypass the closed throttle plate. Its small ports are easily clogged and sometimes a cleaning can remedy some stalling and rough idle.
If your other performance is good, like during starting and acceleration, I'd rule out a fuel delivery problem. Often, fuel starvation will cause hard starting and poor or uneven acceleration.
A vacuum leak will also cause rough or higher than usual idle without necessarily resulting in the performance problems associated with poor fuel delivery. All the air that passes into the engine should flow through the air filter, past the throttle, and into the intake manifold. There are a variety of sensors and methods for detecting that amount of air and that data is critical to the engine computer. If air is leaking into the intake manifold such that it bypasses the sensors, the computer might not be able to compensate for the extra air during some circumstances, like at idle for instance. A broken vacuum line could cause this at an idle but become less noticeable at higher RPMS when the airflow into the engine becomes so great that the small leak doesn't make as big a difference.
This kind of air leak almost always turns the check engine light on also. The code would be P0171, System too Lean Bank 1.
You didn't mention, however, if the throttle cleaning did fix the stalling and rough running.
posted by Jon-o at 6:34 PM on December 31, 2009
If there were fault codes (like P0505 or P0506, for instance) for the IAC (idle air control) valve stored, a quick and cheap fix is to clean the throttle body. It's pretty common for carbon and gunk to foul up the throttle body and cause poor idle. Basically, the throttle itself is a valve that controls the flow of air into the motor when you press the accelerator pedal. When the car is stopped and the throttle is closed, the engine needs a minimum air supply to maintain an idle. The IAC is a computer controlled valve that allows air to bypass the closed throttle plate. Its small ports are easily clogged and sometimes a cleaning can remedy some stalling and rough idle.
If your other performance is good, like during starting and acceleration, I'd rule out a fuel delivery problem. Often, fuel starvation will cause hard starting and poor or uneven acceleration.
A vacuum leak will also cause rough or higher than usual idle without necessarily resulting in the performance problems associated with poor fuel delivery. All the air that passes into the engine should flow through the air filter, past the throttle, and into the intake manifold. There are a variety of sensors and methods for detecting that amount of air and that data is critical to the engine computer. If air is leaking into the intake manifold such that it bypasses the sensors, the computer might not be able to compensate for the extra air during some circumstances, like at idle for instance. A broken vacuum line could cause this at an idle but become less noticeable at higher RPMS when the airflow into the engine becomes so great that the small leak doesn't make as big a difference.
This kind of air leak almost always turns the check engine light on also. The code would be P0171, System too Lean Bank 1.
You didn't mention, however, if the throttle cleaning did fix the stalling and rough running.
posted by Jon-o at 6:34 PM on December 31, 2009
Response by poster: I just got the car back today, and didn't have a chance to drive it more than a couple of miles, so we will see over the next couple of days if that fixed the issue or not. The way back seemed smooth enough, but the mechanics test drove it for a long time when they had it, and they never got it to act up at all, so we will see how things go.
posted by markblasco at 1:56 AM on January 1, 2010
posted by markblasco at 1:56 AM on January 1, 2010
Response by poster: Oh, and the check engine light never came on.
posted by markblasco at 1:57 AM on January 1, 2010
posted by markblasco at 1:57 AM on January 1, 2010
...so it could be an IAC (Idle Air Control) valve.
This was my first thought, too. The symptoms are classic IACV failure. It could also be signs that the Mass Air Flow sensor is beginning to fail (though, in my experience, a MAF simply fails all at once, rather than give warning signs. YMMV.)
posted by Thorzdad at 7:36 AM on January 1, 2010
This was my first thought, too. The symptoms are classic IACV failure. It could also be signs that the Mass Air Flow sensor is beginning to fail (though, in my experience, a MAF simply fails all at once, rather than give warning signs. YMMV.)
posted by Thorzdad at 7:36 AM on January 1, 2010
This thread is closed to new comments.
posted by Greg_Ace at 1:31 PM on December 31, 2009