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Old 04-17-2016, 11:03 AM   #1
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Default She won't idle right!

I need some help guys. Got a 96' Olds 88 w/ about 230k miles on her. Got the 3800 series, 3.8L under the hood as I'm sure you all know. Been a great car to me, I've only had to replace the normal preventative maintenance parts and it'* started every time I've turned the key.

Recently I noticed the vac hose that runs from the throttle body to the fuel pressure regulator was chewed right through by mice or chipmunks I assume. I changed the hose and started her up, ran fine for about 5 minutes and then it started to surge worse and worse until it quit. CEL was on, gave me a P0171 too lean code. If I gave it some throttle, it would keep running as long as I held it. That, and it would idle fine if that vac hose was sucking air. Which is what it was doing with that hose chewed through I suppose. Makes me wonder how long that vac hose was mice food. Didn't notice until I saw it because she was running just fine. So to sum up: it starts no problem, it will idle fine for a few minutes and then surge worse and worse until death occurs unless that vacuum hose is disconnected. If I plug it, it'll die.

I cleaned the MAF sensor and checked all the other vacuum lines. Throttle body is clean and I can't find any obvious issue. Fuel pump and fuel filter are pretty much new, got plenty of fuel pressure at the rail. Disconnected the battery for awhile to let things reset. Can't seem to pinpoint my issue. Any suggestions?
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Old 04-17-2016, 05:45 PM   #2
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Here is a list of things to check for P0171:
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

If something chewed a hose better look at all hoses & wires..
When was the last time you changed the spark plugs/ wires?
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Old 04-17-2016, 07:59 PM   #3
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Quote:
Originally Posted by Soft Ride View Post
Here is a list of things to check for P0171:
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

If something chewed a hose better look at all hoses & wires..
When was the last time you changed the spark plugs/ wires?
I checked everything for leaks, seems leak free. Although I found some chewed acorns in my air cleaner box...not enough to cause any running issues though. O2 sensor is fine, fuel pressure is in check. I suppose the injectors could be a little plugged but it runs smoothly for a little while before beginning to surge and then quits. Doesn't appear to be misfiring or running rough, just not running at all at idle unless more throttle is given. Or if I leave that vac hose unhooked. The PCV just pushes down into the intake manifold and has the MAP sensor on top of it. The PCV is good, I checked that.

So I started to lean towards the MAF sensor today and did some poking around. I decided to test it, it only has three wires so that made it easy. Grabbed my voltmeter and hooked the negative tester to my battery and the positive to the signal wire and when I started it. My voltmeter read around 2 volts before even starting it and the reading didn't change much at all as I gave it throttle. Maybe that'* the issue?
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Old 04-18-2016, 11:08 AM   #4
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First, the MAF has three wires....power(12V), ground, and a signal wire....

When you tested the signal wire, you pierced it and got a reading while the engine was running?

Only problem is, you should have been reading, Hz, not voltage(not all multimeters have ability to read Hz).....

Basically, you get a base reading at idle, and then increase throttle opening, and should see Hz readings increase....then close the throttle and it should return to the base reading....

I think you may have a rodent problem.....if spraying carb cleaner around the engine did not cause any idle change, go back to the air box....you had debris in the air filter? Separate the rest of the box to get to the PCM....may find that the little buggers have eaten the insulation of some of the wires, causing problems....otherwise, Soft ride has pointed out some areas of concern.....

Last edited by Tech II; 04-18-2016 at 11:09 AM.
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Old 04-18-2016, 01:42 PM   #5
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Originally Posted by Tech II View Post
First, the MAF has three wires....power(12V), ground, and a signal wire....

When you tested the signal wire, you pierced it and got a reading while the engine was running?

Only problem is, you should have been reading, Hz, not voltage(not all multimeters have ability to read Hz).....

Basically, you get a base reading at idle, and then increase throttle opening, and should see Hz readings increase....then close the throttle and it should return to the base reading....

I think you may have a rodent problem.....if spraying carb cleaner around the engine did not cause any idle change, go back to the air box....you had debris in the air filter? Separate the rest of the box to get to the PCM....may find that the little buggers have eaten the insulation of some of the wires, causing problems....otherwise, Soft ride has pointed out some areas of concern.....
Yeah you're right, I was testing it wrong. Looked it up last night and tested the right way by back probing and switched my multimeter to hz while hooked up to the signal wire. I let her warm up first and then did my test. The value kept bouncing between 0.0 hz and 0.05, regardless of throttle position. I think I may have found at least one of my problems. Next problem is the auto parts store wanted 200 dollars for the MAF sensor! Bought a new one online for 35 bucks instead
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Old 04-19-2016, 05:02 PM   #6
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Before replacing, always clean the sensor element with MAF cleaner.....

Also, Hz readings will not be constant.....they will vary, even at idle....whatever you get for a reading at idle, make note of it and the variation.....now increase throttle opening....should see Hz increase.....now close it and it should go back to the original idle reading(same variation)....

Did you check the wire harness at the PCM in the air box for damage by rodents?
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Old 10-26-2016, 07:59 PM   #7
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Did this fix your problem? Mind sharing thye site taht you picked up the MAF Sensor?
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Old 10-27-2016, 07:56 AM   #8
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Did this fix your problem? Mind sharing thye site taht you picked up the MAF Sensor?
I see that this thread is old but I too also wonder if that cheap MAF fixed the problem. I tried one of those NEW $35 MAFs a while back and it caused more problems than it solved. Go with a used HITACHI instead.
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