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Discussion Starter #1
Well I have seen similar problems on forums, but nothing exactly like this:

I got aware of the problem when I began taking longer trips (2 hour drive). The car always runs fine until halfway through the trip. By then, it begins to stutter and jerk, as if it were getting a bad mix of air/gas. I sort of control this by applying less pressure on the pedal and keeping it steady, but it worsens as I keep on running.

At first, it wont accelerate over 5000rpm. If I try to get it over that it will stutter and lose power (even if I rev it on neutro). After that it gets worse. As I keep on going, it will then stutter at 4500 then 4000 and down to a point where I have to stop and let it rest for a while before been able to continue.

After letting it rest for about 10 minutes, I continue my trip and it runs normally for while, but at some point the problem comes back. I don't know what could be happening, but I have to point out a few observations.

1) The car has a custom made air intake that doesn't end on the fender like some setups I've seen, the filter instead rests on the side near it, but still inside. The same problem happened with the stock intake which was the reason a custom one was installed although it now seems that it didn't work.

2) The problem rarely happens when driving at night or at cold temperature conditions like raining. In fact if I am driving on a rainy night, the problem doesn't happen at all. On the other hand on hot and sunny days (specially at the 11am to 2pm range) the problem happens a lot easier and a lot earlier on the trip.

3) A trick I have been using is that when the problem happens and I am on a mountain road as I go down the slope I put it on neutro and just let it roll down. This seems to somehow alleviate the problem and lets me acelerate the car to its normal rpm once the slope ends and I am go into gear again.

4) At rare occasions when the car is having this problem, as I keep running all of a sudden it seems to fix itself.

5) The engine is apparently NOT overheating, because the temperature needle always stays in the middle or below.

6) I havent scanned the cars computer so I don't have any codes, but I will probably go get it scanned this week.


Some people have told me that I could be having a bad MAF sensor, others tell me that the intake system is not working because it is sucking up hot air. I only know basic stuff about mechanics so I am not sure on what to think. Any suggestions would be greatly appreciated.

Thanks in advance
 

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Black 2001 RS
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What maintenance has been done recently? How many miles on the car? And where are you located that it's getting hot? It's fairly wintry in the Northern Hemisphere.

Since this issue is sporadic, it seems sensor (or electronics) related. One part that doesn't seem to like heat too much is the coilpack.

Can you pull the spark plugs and take a look? Check for the correct gap, or replace them if it's time.

If you leave it in gear while coasting down a hill, the ECU turns off the injectors, so you're using no fuel at all, thus not creating more heat. But do what works.
 

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Discussion Starter #3
What maintenance has been done recently? How many miles on the car? And where are you located that it's getting hot? It's fairly wintry in the Northern Hemisphere.

Since this issue is sporadic, it seems sensor (or electronics) related. One part that doesn't seem to like heat too much is the coilpack.

Can you pull the spark plugs and take a look? Check for the correct gap, or replace them if it's time.

If you leave it in gear while coasting down a hill, the ECU turns off the injectors, so you're using no fuel at all, thus not creating more heat. But do what works.
Thanks for replying.

I live in Puerto Rico, so been a caribbean island, it can get pretty warm in the middle of the day.

The car has aprox. 100k miles (I say aprox because the speed sensor broke down and I spent 3 weeks using the car like that).

The spark plugs need changing and I will also do that this week. I found out that some of them are a little wet with oil, which points to a gasket problem, but I don't think that this is causing the stuttering.

I thought that the off gear thing on going downhill seems worked because the engine stays at idle so I guessed that heat decreases and the problem dissapears for a while. What you say makes complete sense, so who knows.

I made another one of those trips today. Drove for hour and a half from 11am to 12:30am and the car only had problems at the last 10 minutes or so. The problem became bad when I drove it a couple hours later after letting it parked on a place in which it was directly hit by sunlight, but as I said before it was sporadic.

When I had to go back, it was already nighttime and there were no problems on the trip back home. It was kind of surprising because I even floored it, trying to get home faster and it responded perfectly. So it seems that temperature is an issue.
 

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Discussion Starter #5
When was the last fuel filter change?
2 years ago when I got the car. At first, I wondered if the fuel filter could be the culprit. It would make sense because the problem happens when I press the gas pedal and it accelerates to a certain point, but since the problem happens mostly on hot temperatures and because cool temperatures basically make the problem dissapear, I have ruled that out all this time.
 

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2ooo RS coupe
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it sounds like the map sensor is beginning to fail, all the symptoms you mentioned is pointing to that, it can be very expensive for that little sensor, so the best way is to barrow from another car subaru of course, and see if it makes any difference, yup i have seen map went bad without any cel or dtc shown at all, and almost all acts up when the engines are caliente. good luck guy i hope this helps.
 

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Discussion Starter #8
it sounds like the map sensor is beginning to fail, all the symptoms you mentioned is pointing to that, it can be very expensive for that little sensor, so the best way is to barrow from another car subaru of course, and see if it makes any difference, yup i have seen map went bad without any cel or dtc shown at all, and almost all acts up when the engines are caliente. good luck guy i hope this helps.
Thanks for the tip, I will check that out.
 
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