'98 Olds 3800, tries to die at idle, no MIL

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'98 Olds Intrigue 3800, 175K miles, having issues beginning a couple days ago. Seems to only happen after it's warmed up (so far). At idle it will try to die, RPM's will dip way down, then it will
flare up to about 2000 RPMs. No MIL during these episodes, and the only stored code scanner gave me was one of the O2 sensors was out of range at some point. It hasn't exhibited this condition any other time, like going down the highway, or when it's started cold. Only seems to be after it's warmed up. Since there's no MIL, I suspect the fuel pump. I doubt the fuel filter is the culpit since it doesn't act up at or going up to highway speeds, when the engine is calling for more fuel. I don't want to go to the expense or hassle of changing the fuel pump without being as sure as I can be that's the problem. The problem is intermittent, which in my experience is how fuel pumps can be when they're beginning to fail. And that also makes it difficult to catch by putting a pressure gauge on it. I don't know if the fuel pump has been replaced in the past, and if not, it's about due. Given the conditions I described, and no MIL, does this point strongly to the fuel pump? Or is there anything else I should look at first?
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blowout preventer wrote:

Fuel pump runs at constant speed. Excess pressure is dumped via the regulator. You would notice a bad pump under load or high speed. It would run just fine at idle since the car does not need a lot of gas then.
Things to check. None of these will set a code: 1. dirty or bad MAF sensor. 2. throttle mouth and butterfly covered in gunk 3. bad IAC valve 4. bad intake manifold- If you have not already had the intake manifold replaced, then it would be a VERY good idea to have it checked... or replaced. Immediately.
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Paul wrote: "...Things to check. None of these will set a code: 1. dirty or bad MAF sensor. 2. throttle mouth and butterfly covered in gunk 3. bad IAC valve 4. bad intake manifold- If you have not already had the intake manifold replaced, then it would be a VERY good idea to have it checked... or replaced. Immediately.
****************************
I actually replaced the upper and lower intake gaskets and plastic plenum about 10K ago, and during that operation I cleaned around the throttle plates and bore. I most likely viewed the MAF sensor during that time and saw nothing wrong with it, but I will check it again. I would have thought a malfunctioning MAF would give a code or a MIL, if it gave a reading that was out of range, but apparently not. It sounds like the MAF or especially the IAC are likely culprits, but how exactly do you check them?
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blowout preventer wrote:

however... The maf should be nice and clean. Not much else to the device. I forgot what the voltages should be... perhaps it is online somewhere. The iac is not easy since it will have to come off to clean and check. They fill up with carbon. There should not be much wobble on the pintel. You can step it with a 9v battery.
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blowout preventer wrote:

however... The maf should be nice and clean. Not much else to the device. I forgot what the voltages should be... perhaps it is online somewhere. The iac is not easy since it will have to come off to clean and check. They fill up with carbon. There should not be much wobble on the pintel. You can step it with a 9v battery.
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The MAF (at least on OBDII 3100) puts out a varying frequency not a varying voltage, not sure about 3800 SII. I connected one of mine without the rubber hoses to a 12v source and a speaker and I could hear the frequency of the whine (signal) go up just by waving a piece of cardboard on the other side of the room or by walking around in the room. I had no idea before that MAFs were that sensitive.
A good scan tool is helpful here, not just a simple code reader. Something like the OTC 4000 enhanced or Genisys and their rebrands (Mac Mentor, ETC.) will show MAF flow both in terms of frequency and in terms of mass flow like Lbs per minute. It will also show a weak fuel pump or plugged filter via the long and short term fuel trims.
My '97 Lumina chugged and hesitated when started hot but otherwise ran OK and it was because one of the fuel pump's brushes' copper flex leads was corroded away so the current was passing through the steel spring instead, the spring acted as a resistor and reduced the voltage to the armature hence slowing the pump down. The scan tool showed normal long term fuel trims at idle but way high (+20% IIRC) positive trims under load at high RPM. The chugging on restart was due to the engine heat vaporizing the fuel in the rail, normally the vapor would be flushed back to the tank via the return line as soon as the pump started but the pump was running too slow to develop enough pressure to open the fuel pressure regulator hence the vapor stayed in the rail and went through the injectors instead, which caused a temporary lean condition.
It amazes me how much OBDII cars can adapt, the car ran great except for at hot restart and had no return flow at all due to low fuel pressure.
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Daniel who wants to know wrote:

Cool! Thank you for the info, Daniel. Its good to learn new things.
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On Tue, 20 Sep 2011 18:41:38 -0500, Paul in Houston TX

My '88 Celebrity had a hot restart issue for a while. That was OBDI. Wouldn't restart one warm evening when I was picking up fried chicken. Instead of running the battery down I jumped on a bus to get the chicken home. Chicken cools off faster than an engine. Simple physics. Then had my wife drive me to the car in the morning on the way to work, and follow me to my mech and then take me to work. We worked across the street from each other and the mech was on the way. Sure enough, it started right up in the cool morning, and ran flawlessly as ever for the 6 miles to the mech. Mech called me to say it was ready. New fuel pump. When I picked up the car he told me he was amazed I drove that car in there. Had 3 psi fuel pressure.
My '93 Grand Am would stall when the gas gage hit 1/4 tank and you hit the brakes to stop reversing. Didn't even test the fuel pressure, my son just put a new pump in. Fixed that.
The only times I've had that racing like the Olds was when the idle was relearning, and a bad ECU that eventually failed completely. The bad ECU was in a throttle body Corsica 2.0. Glad it failed, because I was about to throw a new throttle body at it. After checking out what the guys here have recommended, if nothing helps, give some though to swapping in a different ECU.
Dan, I've got a '97 Lumina with 160k on it now, and it runs like a top. Done a few of the more "rare" things on it like LIM gaskets and lower engine mount. LIM was just preventative because the OEM gasket often fails, and the lower mount rubber just wore out. If you do the LIM, get the Felpro metal rimmed gasket, and this. (Amazon.com product link shortened)16566981&sr=8-1 The 3.1 LIM is harder to do than the 3800. Just more crap to move out of the way. Don't use the shop manual procedure for that lower mount. It's ridiculous, removing the ball joint, etc. I saw a guy's web page showing how he does it. Just unbolt the top dogbone, jack the engine up a bit, and remove and replace the mount through the wheel well. That's what I did. Piece of cake.
--Vic
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Ours was an '87 Celebrity wagon 2.5 Iron Duke/Tech 4. It did the same thing, first it wouldn't restart hot but was OK if left running then it started dying. The shop fixed it and part of the fix was a new TBI fuel injector, some time later it would start, run for a few seconds, and die. If the alternator was unplugged it would run flawlessly so I hooked up a battery charger and noted that when the voltage went above 14 it would die, It turned out that the new injector was defective and was shorting out under load and tripping the ECM's protection circuit (it ohmed out fine). I confirmed this by hooking a resistor in series with the injector and noted that the engine stayed running at full operating voltage with the alternator plugged back in. I had the new injector replaced under the 1 year warranty and it ran fine again.

(Amazon.com product link shortened)16566981&sr=8-1
Thanks for the tool tip, I may need it as I have 2 OBDII Luminas with the 3100, a '96 LS with Cal. emissions and the aforementioned '97 base Fed. emissions. Both have bad turn signal switches currently and the '96 has bad tires. Why can't all cars have separated stop and turn lamps like my GF's '91 Tracker 4x4?
FWIW I now understand the sentiments of those who say that they will never buy another automatic trans car, I put a newer engine (a '94) in the Tracker and it is the first manual trans car I have ever driven and I already love it, granted I have been driving farm tractors for a couple years now and can rev match shift some of them without the clutch, but I didn't think driving a manual without an engine governor could be so easy or fun. I haven't killed it yet but she killed it twice in a row when she forgot to release the hand brake LOL.
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I decided to continue to drive the car to see if the problem would change or get more pronounced, possibly making it easier to diagnose. I took it on a trip last night about 120 miles, and it acted up here and there at idle/low speeds between stoplights, etc. -- but on the way home, it cut out HARD several times as I was approaching 55 mph. This was after it had been shut off briefly and re-started and took off downthe highway. After that, it ran approximately 45 minutes between 60-70 mph without incident. So I guess it's not the IAC anyway. Does that still point to the MAF?
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blowout preventer wrote:

Nope. It sounds like your first intuition about fuel pump was probably correct. Cutting out under load is a good indication. Can you put a pressure gauge on the shrader valve?
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Paul wrote, "Nope. It sounds like your first intuition about fuel pump was probably correct. Cutting out under load is a good indication. Can you put a pressure gauge on the shrader valve? " ******************************** Yes I figure I will buy a fuel pressure tester tomorrow. I don't need a fancy one of course, so I will buy an inexpensive one since I won't use it very often. Any recommendations which one to buy / stay away from?
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blowout preventer wrote:

I can't recommend any commercial brands. :( I always made my own out of armored hose, a 0-100 gauge, and a shrader adaptor since I always seem to have those things in a box or drawer somewhere.
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Paul wrote, "Nope. It sounds like your first intuition about fuel pump was probably correct. Cutting out under load is a good indication. Can you put a pressure gauge on the shrader valve? " ******************************** I drove it today to get a fuel pressure gauge and deplete the remaining fuel, anticipating a fuel pump change. It acted up here and there as it has been doing, but coming back home and approaching highway speed, it cut out hard and the MIL came on. Tested fuel pressure when I got home and it was between 40-45 psi -- and it even started to act up during the test but fuel press stayed steady. Checked the code with an Innova scanner/reader (sort of a higher end one) and it says MAF.sensor (had no codes before). With it idling, I put scanner in real-time data and the reading for the MAF seemed to hover around 0.500 -- even while the engine was dying out, then flaring, etc. I don't know if that number is voltage or a freq reading like the other poster mentioned. Check engine light didn't come back on during this. Apparently the MAF is the culprit, whether it be dirty or worn out (better than a $300 + Delco fuel pump and all that hassle). Went to remove the MAF to inspect, clean or replace, and it uses those torx-looking screws with the tiny post prodruding up the middle. I presume any NAPA or someplace has the tool for those. What do you call that type of fastener (and what's the purpose of it)? Gotta buy the whole set, or is there only one size that uses that type? Thanks for all your input..
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blowout preventer wrote:

Those are anti-tamper Torx. Very common on newer vehicles.
If you want to clean it just blast it with some good electrical cleaner from the intake duct connection. I have only had one MAF that cleared up after cleaning. Usually they just die.
--
Steve W.

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blowout preventer wrote:

The fuel pressure reading is reasonable. Back to electrical again. A MAF will give a faulty reading due to lots other conditions and it not really a bad maf. Low rpm can set a bad maf reading. One of the things I would look for right away is a bad crank sensor. They often exhibit the symptoms you describe. They go bad due to heat in about 10-15 years. Unfortunately, there is no easy way to check a Hall sensor. www.mightyautoparts.com/pdf/articles/tt64.pdf
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Paul wrote, "Security Torx. The fuel pressure reading is reasonable. Back to electrical again. A MAF will give a faulty reading due to lots other conditions and it not really a bad maf. Low rpm can set a bad maf reading. One of the things I would look for right away is a bad crank sensor. They often exhibit the symptoms you describe. They go bad due to heat in about 10-15 years. Unfortunately, there is no easy way to check a Hall sensor. " ****************************** Tried tapping the crank sensor as per the article, didn't make a difference. Then I disconnected the MAF, which lit the MIL, and then drove it around like that, and after a few minutes it acted up just as it has been. So that points away from the MAF, since it was out of the loop. And it sounds like the crank sensor. And, given the age and mileage of the car, the symptoms, and the fact that they're known to go out about this point anyway. In other words, if I plan on keeping the car (which I do) -- I may as well replace that anyway, since I'll have to do it at some point anyway, and probably coming up pretty soon. And then, with any luck, that will be the end of the problem. I thought about robbing one off of a junker to see if that changed anything, I haven't looked in to how to change it -- just unbolt it? Or does the balancer have to come off?
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blowout preventer wrote:

The balancer has to come off and that may not be easy. It took a 3/4" impact to get the one off of my own car. The sensors are all different. Yours is a hall sensor and is checked with a scope. I agree with replacing it. It will go bad eventually anyways and when it does finally quit it may not be in a good place.
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As an aside, why doesn't the onboard diagnostic system simply give me a code for crankshaft sensor? Or any sensor, for the most part? Apparently the signal that the sensor (or SOME sensor) is providing is either weak, intermittent, non-existent at times -- or WAY out of range in any case. Why doesn't it immediately light the MIL and provide a code? Isn't that the purpose of the whole system? Instead, it provides a code for something that ISN'T the problem -- undoubtably leading countless people to purchase sensors, etc they don't need. Seems like a conspiracy. With all their "technology" and stuff, they should be able to pinpoint the problem a lot better than this. That's what I thought the whole system was for. This isn't much better than just hangin' parts. Just venting.
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I bought a Delco crankshaft position sensor and went to change it out, but decided I wouldn't be able to get the harmonic balancer off, as my puller probably wouldn't fit right to pull it. Figuring that the labor wouldn't be that much with the correct puller, I took it to the GM dealer (I was right -- an hour labor to change.) They said they would rather diagnose it themselves to ensure they weren't changing the part that didn't need it, and I gave them the go-ahead. They diagnosed it using a tech 2 and said everything points to the MAF. My Innova scanner said the same thing.
HOWEVER, after MY scanner had indicated the MAf, I unplugged the MAF, and the engine still cut out, flared, etc. aferwards. I n other words, it exhibited the exact same problem in open loop without the MAF even in the equation.
SO... Should I just have them change out the Crankshaft Position Sensor, like I originally was going to have them do anyway ( since it has 175K on it and is probably due -- plus the engine dies ect. without the MAF plugged in, thus indicating something other than the MAF)?
OR... just change the MAF myself, which costs $200 and might not change the problem?
In other words, if scanning it with both my Innova, AND a Tech II by a pro, and they both indicate the MAF -- but the engine still acts up without the MAF even plugged in... What would you do?
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