Just got my new 3800sc back. Bone stock installation. Everything seems pretty good, but the idle is hunting between 500 - 1100 with occasional surge to about 1500. At the low end it's very close to stalling. Any common causes I can look at?

Check your fuel pressure. Scan and see if the temp sensors are looking right. Make sure the TPS is showing the throttle closed. Are there any codes present?

Will have to check the fuel pressure tomorrow, light is gone for the night. Here are the codes I'm seeing:

* P0102 Mass or Volume Air Flow A Circuit Low
* P0650 Malfunction Indicator Lamp (MIL) Control Circuit
P0102 Mass or Volume Air Flow A Circuit Low
P0650 Malfunction Indicator Lamp (MIL) Control Circuit

It would be the MAF.... couldn't be some $20 part, or the TPS, which I still have one brand new because I never got it swapped onto the 3800sc I blew up last month

[This message has been edited by NetCam (edited 08-08-2014).]

quote Originally posted by NetCam: Will have to check the fuel pressure tomorrow, light is gone for the night. Here are the codes I'm seeing: * P0102 Mass or Volume Air Flow A Circuit Low * P0650 Malfunction Indicator Lamp (MIL) Control Circuit P0102 Mass or Volume Air Flow A Circuit Low P0650 Malfunction Indicator Lamp (MIL) Control Circuit

Unplug the maf and see if it goes away.

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86 SE Convertible 3800sc 4t65e HD.

Going to give that a shot, if the problem goes away, will try taking the sensor off and cleaning it. Apparently those have the 'safety' torx screws on them. Will have to see if I can find them anywhere or if I'll have to break out the ol' vice-grips

[This message has been edited by NetCam (edited 08-08-2014).]

Harbor Freight sells a set that includes the correct bit for cheap.

You can Dremel a straight screwdriver slot in the top of the screw.

I got a set of 'tamper proof' torx bits from Princess Auto (sorta Canadian equivalent of HF). Disconnected the MAF, started the car and it stalled almost immediately. Plugged it back in and same thing as before, hunting from 500 - 1100. I took the sensor off and gave it a good cleaning with some brake cleaner, put it back on and nothing seemed to change.

What are you getting for MAF flow at idle? On my 98 3800 NA I get about 1 lb/min or 2,729 hz,

You didn't hook up your MIL light?

[This message has been edited by phonedawgz (edited 08-10-2014).]

When I checked my readings from yesterday, the MAF started at 7.89 and was bouncing around between 5 and 8 at idle. Then at some point during my trip, the reading stuck at 14.74 and didn't move for the rest of the trip. I just went out and started the car, let it run for 3 or 4 minutes, and got a zero reading on the MAF for the entire time. Idle bounced around between 690 and 935.

7.89 g/s = 1.04 lb/m which is close to what I get so at a slightly faster cold idle that sounds right. The number bouncing around would indicate the difference between the engine running faster and slower, so that seems right also if the numbers are staying with the engine speed.

0 now however is a problem.

First try this. With the scanner hooked up wiggle around the MAF connector. Any chance moving it around makes the numbers come back or move around? Bad connector? Something else to do is if you get the sensor giving you a reading it to tap on the MAP sensor and see if the numbers move around.

Do you have +12 on the Pink wire of the MAF? The best way to test is by backprobing the connector with the sensor still plugged into the connector. If you do have +12 on the Pink then check using the Black/White of the connector as your reference ground. Finally if you have the ability, check for the frequency produced on the yellow wire again using backprobing

http://easyautodiagnostics..../index-of-articles-1

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You will have to get your MAF working again of course

BUT

It's not the cause of your trouble. With the MAF producing zero you are still getting a surging idle. So the trouble can't be coming from the MAF sensor.

MAP sensor reading correctly? Key on engine off do you get 30 in/Hg? Is your MAP sensor connected to Lower Intake Manifold vacuum?

Finally check your fuel pressure.

[This message has been edited by phonedawgz (edited 08-10-2014).]

I don't have a wire piercing probe to run the tests. Is there another way to do this without damaging the wires?

BTW, I did notice this (after reading that brake cleaner was good to clean a MAF)

Tip 2: It's very important the you do not use carburetor spray cleaner or brake cleaner. Both of these are very harsh solvents and can damage the inner circuitry of the MAF sensor. If the MAF wasn't BAD to begin with... it will be -if you use these two solvents (this I can vouch for from personal experience too)

This would explain why I'm getting a zero reading after cleaning when I was getting reading before.

You don't want to pierce the insulation of the wire. What you want to do is slide the pin up past the seal of the connector without damaging the seal.



Piercing the insulation of the wire would be bad.

Thanks, will stop at Staples on the way home from work tomorrow and pick up some pins.

After reading all the directions, they said 'The most important tool that you're gonna' need is a Digital Multimeter that can read high Hertz (Hz) Frequency'. Don't think I have one of those so I guess I'm going to be adding to my toy collection.

Did the tests today.

TEST 1: Testing the Power (12 Volts) Circuit - I got 11.3 Volts. Not sure, but think this is OK? Not sure if close is close enough here, this could be because my connections weren't perfect.

TEST 2: Testing the Ground Circuit (12 Volts) - I got ~11.9 Volts. Figure that has to be close enough.

TEST 3: Testing the MAF Signal - At idle I was getting around 2.9Hz give or take. When I gave it some throttle it went up steadily and then back to around 2.9 at idle again.

I'll take the car for a run and make sure I'm up to full operating temperature and try the tests again, as well as record the data from the MAF while I'm driving.

[This message has been edited by NetCam (edited 08-23-2014).]

Couldn't run the tests again, but did manage to get a look at the MAP readings vs. the idle, and there doesn't seem to be much corelation between the two. I did notice the O2 readings were all over the place, but have no idea if that points to anything. Here's a graph of the idle period when warm.



Edit to add - After checking all the readings (which is painful because you can't export the numbers from the tool, you have to look at them) I noticed that the first time I stopped to let the car idle, the MAF reading stuck at 5.29 and stayed that way until I accelerated, at which point it jumped briefly to 23.71, only to drop and stick at 16.49 for the rest of the trip, which included stops and starts, and a highway run with RPM up to about 5,000. So from what I know about how a MAF works it shouldn't be possible, but it looks like it's 'sticking', but even though the reading from the MAF isn't changing, the revs at idle got up to over 1,100 RPM a couple of times and in the low 500 range about half the time.

[This message has been edited by NetCam (edited 09-14-2014).]

Car should idle/run fine without the MAF if the MAF is the problem. You have other problems if not.

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Turbo 3800 E85 F23 5spd spec5
10.91@133.1

As mentioned before, when I unplugged the MAF the car wouldn't idle at all. Still trying to see if there's something wrong with the MAF, which I think there is. The code is still there, and these readings certainly don't look right.....

So what is the consensus based on the info above? Is the MAF toast or is there a chance it's something else? The part from my local parts store is $170 + tax so I really don't want to pick it up if it's not going to solve the problem.

quote Originally posted by NetCam: So what is the consensus based on the info above? Is the MAF toast or is there a chance it's something else? The part from my local parts store is $170 + tax so I really don't want to pick it up if it's not going to solve the problem.

Go to the yard or ebay. A used MAF should be no more than $30. Hell you can get a complete TB with MAF for $30.

I was gong to take the MAF sensor off my Grand Prix and put it on the Fiero to see if the problem went away. I was told the sensor on my '08 GP is the same one used on the 2001 Bonneville, but looking it up on Rock Auto the part doesn't even look remotely the same.

Anybody have any ideas what else I can check to figure out my idle problem? I still haven't figured out why it stalls when I remove the MAF, from what I understand it should continue to idle.

Unplug the MAF before starting it, not while it is running.

Per your meter your MAF is toast

[This message has been edited by phonedawgz (edited 09-14-2014).]

Thanks, unplugged before I started the car and I didn't have the stalling problem. Idle was really rough at first, close to stalling but not quite. After driving for a while it settled down, but still hunting a bit (between ~600 - 900 RPM). Going to put a new MAF sensor on and go from there. No sense trying to find out if there's another problem until I get this one fixed.

Try cleaning it first, that's the cheaper solution.

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86 SE Convertible 3800sc 4t65e HD.

My 3800sc started almost revving like that, sounded like it had a huge camshaft till it stalled out. Ended up being the o2 sensor I must of killed when I had washed the engine hot. New one fixed it. Just an idea..

I was thinking about O2 sensor as well, but I have no idea what the readings are supposed to look like. Here's a snip of the readings from my last trip. Over about a 3 minute period, the readings are all over the place....

By your readings the MAF is failing. However I would definately start looking for air/vacuum leaks. OBDII PCMS can go into a limp in mode when the MAF takes a dump and use you MAP data to at least get you where you have to . This will normally cause your throttle response to be crappy but will normally idle. A large enough leak can cause a low MAF flow code. But yours looks like it drops out warm.
With most 3800s with bouncing idle it is a leak around the throttle body. Broken/split tees, split hose ends that are not obvious to see. Those will cause lean conditions near idle, but off idle the O2 will start to go normal again due to the engine using more air than can pass through the leak.
Your upstream O2 looks good. The downstream (S2) should bounce when cold, but then when warm, if you have a converter should bounce, but closer to center. Where it staying at .45 leads me to believe it is disconnected.

These readings were actually with the MAF disconnected to see if things leveled out with it off, but they didn't. In fact I took the car for a short trip tonight and while sitting at a light the idle was bouncing from ~400 to close to 2,000 RPM so worse than ever. I don't have a CAT, just stock 3800 manifolds going to a Magnaflow muffler.

Is your PCM re-programed for your specific combo? A 97-98 MAF is a different table than 99+ MAF.

Good question, I'll have to check on the programming, but was going on the assumption that the tune was updated to reflect the change to the 2001 SSEi engine.

Don't know much about your set up but is it possible to mix up the two o2 sensor wires
you could rule it out if it had ever run right.

It would be a long shot, i'm just trying to imagine what it would run like with them swapped

That would be highly unlikely, didn't have this problem with the old engine and I'm using the same harness. Good thought though....

Got the new MAF from Rock Auto yesterday, dropped it in today (Nice when a 10 minute job actually takes 10 minutes). Took it for a spin and it seems my idle problem is gone, but it was only a short trip, just enough to get it up to operating temperature which is where I had the problem before. Looking at my readings now, it looks like my MAF output is pretty much mirroring my RPM/Throttle position, which is what I would expect to see.