01 LeSabre: Poor drivability and P0102

[DrRadar]

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.

[DrRadar]

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.

[Tech II]

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....

[Blue Bowtie]

Originally Posted by Tech II

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.

[DrRadar]

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.

[DrRadar]

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?

[Tech II]

Yes it can.....

[Blue Bowtie]

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.

[DrRadar]

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

Thanks for all the help.

[Blue Bowtie]

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.

[DrRadar]

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.

[Blue Bowtie]

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