Unstable idle on warm weather... fuel pump?
04-24-2002, 08:56 PM
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Unstable idle on warm weather... fuel pump?
I took the 911 to the mechanic, as an oil change was due, and told him to replace the temp sensor, as my idle would oscillate between 800-1200 RPM when in warm weather.
The guy now tells me that he has noticed a clear low fuel pressure when the car is warm (itīll take 2 or 3 - 3 sec cranking to get it running with a warm engine in warm weather). He says itīs probably a fuel pump problem... is he pulling my leg (&wallet) or is he ok? I know the guy is reputable porsche mechanic, so no reason for distrust... other than this boardīs infinite knowledge
The guy now tells me that he has noticed a clear low fuel pressure when the car is warm (itīll take 2 or 3 - 3 sec cranking to get it running with a warm engine in warm weather). He says itīs probably a fuel pump problem... is he pulling my leg (&wallet) or is he ok? I know the guy is reputable porsche mechanic, so no reason for distrust... other than this boardīs infinite knowledge
04-25-2002, 03:18 AM
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my 84 has the same 'unsettled idle' when the car is fully warmed up (driven for awhile) and then forced to sit (usually heavy trafic) without braking 2500rpms in 1st or driven otherwise quite slow (read: no wind cooling) and each time I notice the car idling odd the car seems to be hovering just below the second white temp mark (2nd up from the bottom "temp bar" signifiying your car is not fully awake yet)
Best description for those who have never expereinced this: You know your warm-up sequence your car goes through first thing in the morning, with the revs slowly raising to 12-1400 rmps a couple of times on its own? Its just like that, but only not quite as high a rev, and not quite as gradual an idle change. Its not violent, but not really 'happy' either.
2nd best description: I pulled into my driveway one day after following some kid in a riced out Honda for 4 blocks (at 10-under the speed limit!) after spending 30 minutes in (weekend) congestion and encountered the problem again, prompting me to open up the back and poke uselessly around in the engine compartment. My crotchety old neighbor noticed my futile attempts at locating the problem and made the observation that my car sounds like it is "searching for its correct idle speed".
I was hoping that this phenomenon was just a warm idle problem or a thermostat that needed adjusting.
But after reading your post Carlos, I purposely made my car hot - drove it irritatingly slow way through construction zones through town - then drove it hard and fast and noticed that it seemed to run completely smooth and normal.... seemingly contradicting the likelihood of a fuel pump as the root of my uneven-idle issues.
Couple of questions for you Carlos: How long have you been driving around with this oil/since last oil change? Have you tried pushing your car's speed and testing its performance yet when you experience these problems?
My (un)educated guess is that if the car acts and responds differently when the only variable changed is the operating temperature, then the operating temperature is directly related to the problem.
In other words: If you experience a power lag when your car is warm vs when your car is cold, how could it be your fuel pump? Let me know what you discover - I am curious to see if it is in anyway helpful for me in diagnosing this peculiar 'annoyance.'
Best description for those who have never expereinced this: You know your warm-up sequence your car goes through first thing in the morning, with the revs slowly raising to 12-1400 rmps a couple of times on its own? Its just like that, but only not quite as high a rev, and not quite as gradual an idle change. Its not violent, but not really 'happy' either.
2nd best description: I pulled into my driveway one day after following some kid in a riced out Honda for 4 blocks (at 10-under the speed limit!) after spending 30 minutes in (weekend) congestion and encountered the problem again, prompting me to open up the back and poke uselessly around in the engine compartment. My crotchety old neighbor noticed my futile attempts at locating the problem and made the observation that my car sounds like it is "searching for its correct idle speed".
I was hoping that this phenomenon was just a warm idle problem or a thermostat that needed adjusting.
But after reading your post Carlos, I purposely made my car hot - drove it irritatingly slow way through construction zones through town - then drove it hard and fast and noticed that it seemed to run completely smooth and normal.... seemingly contradicting the likelihood of a fuel pump as the root of my uneven-idle issues.
Couple of questions for you Carlos: How long have you been driving around with this oil/since last oil change? Have you tried pushing your car's speed and testing its performance yet when you experience these problems?
My (un)educated guess is that if the car acts and responds differently when the only variable changed is the operating temperature, then the operating temperature is directly related to the problem.
In other words: If you experience a power lag when your car is warm vs when your car is cold, how could it be your fuel pump? Let me know what you discover - I am curious to see if it is in anyway helpful for me in diagnosing this peculiar 'annoyance.'
