01 LeSabre: Poor drivability and P0102

Son is complaining of low power, poor acceleration, and surging, which I confirmed. Read code P0102. Disconnected the MAF electrical and drivability improved. So, need a new MAF sensor, right?

To test that theory, pulled the MAF sensor from my 99 Grand Prix and installed in the 01 Buick. (RockAuto shows they use the same part number.) But the drivability problem remains...disconnected the MAF sensor and improvement. Go figure.

Put the MAF sensor from the Buick into the Grand Prix and it drove fine, at least for the 5-10 minutes I drove it.

I did not clear the codes at any time. Would that result in the poor drivability in the Buick when installed with the supposedly good MAF sensor? I don't think so.

My thought is a potential wiring problem or something other than the MAF sensor tripping P0102. But if this is the case, why would disconnecting MAF sensor improve drivability?

As always, any help is appreciated.

When the maf is disconnected the pcm goes to a default back up setting. Which in your case is better than a failed circuit. Google that code for multiple causes.

Do you have access to a scan tool that can read data?

I have a dongle that Bluetooth connects to phone app that can read some data.

The MAF wiring harness is always suspect. On this vintage Buick 231 V-6 the CTS, TPS, and IAC connectors and harness are also suspect. Most chain parts stores sell MAF connectors, and it isn't due to coincidence.

I agree with Blue....could be one of the MAF connections in the harness or one of the wires to the connector could be broken inside the insulation.

Need to check data to pre O2 sensor....but you would need a scan tool to read O2 data......if data is skewed hi or low, but data is ok, when the MAF sensor is disconnected, then you need an MAF sensor....

I'm out of town for a couple weeks. He'll have to limp along with the MAF sensor disconnected until I get back. Thanks for the feedback.

Disconnecting the MAF seemed to help initially, but my son said the drivability problems returned.

Drivability seems to be getting worse and the P0102 remains; also comes back after resetting it. Verified +BAT voltage an MAF connector and continuity to ground at MAF connector; the signal pin on connector indicated +5VDC, which I suspect is provided by PCM. So it appears that there are no wiring problems to/from the MAF sensor.

I inspected vacuum lines and found a cracked boot which I repaired with no subsequent improvement. No obvious indications of other vacuum leaks although I haven't put a vacuum gauge on it. Replaced PCV valve with no improvement. My Android scan app (ScanMaster) does provide live MAF data; it was showing 0.8-1.0 lb/min in park at idle with increase to as much as 8.0 lb/min (that I saw) while driving. I need to learn how to interpret the quantitative measurements but the MAF does seem to be measuring the air flow. My next thought is to check the PCM/ECM by switching with the 99 Grand Prix GTP....I'm hoping the programming is sufficiently compatible.

Could a failing transmission cause a P0102 and these symptoms? It really seems that the tranny is reluctant to shift and I see RPMs go up to 3000-3500 without the expected acceleration. But putting it in neutral doesn't really improve the behavior. I don't have a scan tool that reads T codes; I hope to "borrow" one from O'Reilly.

As always, any guidance is appreciated.

Happy Memorial Day,

the CTS, TPS, and IAC connectors and harness are also suspect.

The signals at MAF sensor connector appear OK. If wiring problems existed for CTS, TPS, or IAC connectors, would these result in P0102? Or a different code?

They all use the same 5VDC reference supply in the wire harness, and it's not uncommon to find connection problems on these Buick 231s. The IAC only has two stepper drive signals from the PCM and does not use the local ground nor the 5VDC reference supply.

The kicker is that the CTS and TPS are a bit more forgiving, with perhaps a couple of seconds of tolerance by the PCM for signals out of range before an error code is set. The PCM watches the MAF inpuf very closely, however, with as little as 600mS for an out-of-tolerance signal before an error code is set. Thus, a 5VDC supply problem will almost certainly be picked up as a MAF error and may not be picked up as a TPS/CTS error.

Disconnecting the pre-cat O2 sensor did not change performance. The more I drive it to test theories, the more I think it's transmission related. I'll limp to my transmission shop this week and let them check it as I don't have a scan tool that reads trans codes.

Any recommendations for a good "shade tree" scan tool that reads "all" codes (PCM, trans, ABS, body) and live data. I guess freeze frame data would be nice although I have never had access to it so can't say I need it. I realize control functions (like cycling the ABS when bleeding) are likely only in professional models out of my budget. I might be convinced to spend a few hundred dollars on a good tool.

Sorry, I wrote some misinformation in Post #6, and have corrected it....

As for driving the vehicle with the MAF disconnected, that is not a good idea.....running it with the MAF disconnected, is just for testing....

Beware of cheap aftermarket MAF's.......have had a lot of problems buying those, right out of the box.........

Found a couple of holes in the intake plenum that were underneath the wiring harness and fuel lines. One hole is in the gasket trough and the bigger hole is in the top of plenum behind throttle body, directly above the hole to the lower intake manifold. I'm suspicious that whatever is blowing out of the lower intake is hot enough to melt the plenum gasket. Is this common? Is it indicative of another problem that should be addressed?

Photo: https://drive.google.com/file/d/0B5ZhFCsYt2Q3dVdXME1FcWRQRTA/view?usp=sharing

It looks like hot gasses from the EGR tube are melting the top of the plenum.....that should not be happening......gasses are only allowed when the EGR is pulse-width modulated, while cruising....this looks like the EGR is wide open, and sending too much exhaust gasses into the plenum, which will cause no power.....I have seen this happen because of a partially plugged cat, builds up too much back pressure, and it unseats the pintle in the EGR, allowing too much exhaust gasses to enter the upper plenum....it will get to the point where it will actually blow a hole in the top of the plenum.....

So I would have a back pressure check done on the exhaust....this is usually done by removing the pre cat O2 sensor and installing a pressure gage.....rule of thumb is less than 1 psi at idle, less than 3 psi at 2000 rpms....

Got the replacement plenum this week. I'll look into exhaust backpressure once that is installed.

Got back in town today and installed the new plenum. Trying to think ahead before installing the throttle body, I considered removing the O2 sensor first so I could try to check pressure. I then wondered if the excess exhaust pressure may be caused by the EGR valve. How can the EGR valve be tested?

It may be difficult for me to test the exhaust back pressure at the O2 sensor fitting. I'm not sure how best to access it and I don't know if I can get a good seal with the little vacuum/pressure gauge I have.

So if the problem is almost certainly the catalytic converter, I'm willing to proceed with replacing it. But if there's a reasonable chance it's the EGR valve, then may more diagnosis is prudent or replacing the EGR valve first.

I have a short time window to get this thing going because in three weeks I have shoulder surgery and will be unable to do any auto work for at least six months. And I'm traveling one of the next three weeks. So I'm trying to balance the use of my time and money.

As always, any guidance is appreciated.

I reassembled everything, thinking that replacing the plenum would allow the car to run fairly normally so I could get it to a muffler shop. However, it runs no better...like crap. The hard brake pedal suggests insufficient vacuum to the booster, wouldn't you think?

So now I'm thinking a completely clogged catalytic converter. Pondering how to easily relieve some exhaust pressure to test that theory, I took off the EGR valve. No improvement; in fact, after about 20 seconds, the idle increased significantly...alarmingly so. Then considered removing the exhaust crossover just to see if the engine ran any better and to confirm a clogged exhaust theory. But it's too hot to work on now.

Now I'm unsure if it is an exhaust problem or an engine problem. I'm ready to throw in the towel this time and have it towed to a shop. But to my automotive shop or the muffler shop???

As always, any guidance is appreciated.

You can create a gap at the ex manifold and pipe by backing off the bolts....then test drive the vehicle, to see if power has returned.....it will be noisy, but a quick, short trip will reveal if your power has returned due to a plugged exhaust/cat....

You can create a gap at the ex manifold and pipe by backing off the bolts....then test drive the vehicle, to see if power has returned.....it will be noisy, but a quick, short trip will reveal if your power has returned due to a plugged exhaust/cat....

Good point. Plus, if the cat is clogged you'll need to break those stubborn flange nuts free anyway. It's a win-win.

Took the car to a muffler shop because of my time constraints. They said the cat was about 90% clogged. The replaced it for $255...didn't seem like a bad price to me. It drives better but I still have some concerns with "dead spots" during acceleration.

One problem now is the idle is way too high - about 3000rpm in neutral and 1500rpm in drive. Pushing (fairly hard) on the throttle (to close more) reduces idle. I wonder if something happened when I cleaned the throttle body when replacing the plenum...maybe getting rid of the carbon buildup wasn't good in this case. In any event, I think the throttle body may need replacing. A new AC Delco is about $370 and pictures show it with all the sensors (MAF, TPS, IAC). I'm more inclined to get a junker without sensors. A little concerned about this becoming a money pit until it gets to running much better.

Just remembered that the IAC looked questionable when I was replacing the plenum. I was cleaning the carbon build up off of it and unknowingly unscrewed the pintle. Some small bits of plastic fell out. It appears where the pintle screws in is plastic and was the source of the chips. It screwed back in but I thought it might need replacing. Could the IAC cause the high idle?

Yes it can.....

Moreover, the IAC pintle does not actually screw in. When you replace the destroyed one look closely at the old one. You may notice that the pintle shaft does not have a thread - There is no lead-in to the "bumps" on the shaft. That is a rack gear, straight cut. The alternating action of the side gears "steps" the pintle inward or outward depending upon phasing of their operation.

http://www.wwdsltd.com/files/IACCompare.jpg

Borrowed the IAC valve from the Grand Prix to test, and the engine just purred.

Thanks for all the help.

Find your local Dallas wrecking yard and pull an IAC for next to nothing. They rarely fail, other than getting dirty. OTOH, if you want to drop a buck fifty on a new one, that's your call.

Thanks for that tip. But I already ordered from RockAuto. ACDelco $45 less 5%. Off brands are about $20. At that price, the convenience is worth it for me.

That's a much better deal. The chain stores are asking about $150.