I put this here to maximize the readership. If you have or have had replaced your upper manifold (3800 Series I or II, non-supercharged) on your Bonneville and had issues of any kind afterwards (even if you had it done at a GM dealer) this is most likely why:

After installing four Dorman aftermarket intake manifolds and having three cars with issues, seemingly unrelated, I contacted Dorman tech today.

A little background. The first was a '99 Grand Prix GT with a catastrophic gasket failure. I changed the manifold, flushed the engine, and it ran great. But, after selling the car, got a complaint of an intermittent check engine light "O2 lean". The car was now in AL and he took it to a bunch of different places and had a bunch of parts put on. Second was a '97 Park Ave. Same catastrophic failure, same procedure, same "O2 Lean". Checked for leaks all around manifold, brake booster, check valve, t.b, everything I knew. Replaced the O2S. We gave up and the cust has learned to live with the light. Third is a '00 Park. Preventive maintenance with 130K hiway miles. I develops a squealing. In numerous comebacks, replaced w.p, belt, sent him to the A/C place to replace the compressor. They didn't, but put a new balancer on it. It comes back today raising hell. I replace the tensioner pulley, same noise. I started looking for another source. With the engine running, I pulled off the oil cap to remove the engine cover and the noise stopped! I knew right away it had to do with crankcase pressure/vacuum and that meant the pcv valve. I took it out and ran the engine without it and the noise became hellacious!

So I called Dorman. The problem is this: included with the new manifold are a new pcv, new fitting, and new o-ring for the intake. You have to pull the old fitting off the old manifold to get the pcv pushdown spring, but you DON'T have to pull the pcv out, so you don't remove the pcv o-ring to know it needs one! Since there isn't one in the kit, the pcv usually gets intalled without it... instant internal vacuum leak. Some cars get the SES, some make noise, sqeak, squeal, rattle, hiss... I felt stupid til he told me they get dozens of calls PER DAY!!!!

I didn't even get into it with him. He obviously hears enough. (Some guy in The Bronx cussed him out last week.) Dorman is working the pcv o-ring and a little post-it note into all new boxes right now. The tech told me they have 4 MILLION manifolds in service. The most common failure is the egr tube not being installed (stuck in the old manifold, not re-installed or replaced), and there are very few failures aside from that. The second most common failure was over-tightening the bolts and breaking the mounting bosses.

The Dorman manifold also has an extra poind of plastic in it over the GM manifold (the GM manifold is the same as was installed at the factory with NO improvements) The Dorman has .250" of material around the egr tube, GM has .040". The mounting bosses are thicker and the ribs are thicker, too. The t.b. flange is thicker as well. I don't work for Dorman, just telling you what they told me. The revised kit will also include new injector o-rings and two new egr tubes, one to replace to o.e. 97-up 5/8" tube and one to retrofit some of the older 95-97 cars using a 3/4" tube with the later style 5/8" tube.

Don't forget the pcv o-ring!

Its funny how such a small thing can create such a hassle and not many would know the solution. Thanks for the info.

I ALMOST made that mistake. But i checked repeatedly because i could not get the PCV valvo to seat correctly. The o-ring in the factory unit can get very hard to see after years of being installed, but it is in there and can be quite difficult to replace. Luckily i caught it. I did, however, get the O2 Lean code on mine, but that'* more from them being f'ed up by the burning coolant than the PCV IMO. But a vacuum leak... definate lean condition could arise.

Yup..

One of the first things to look at with whistling is the pcv.

We've had 3 or 4 like that here. Narrowed it down to the PCV O-ring each time. Now that'* the first place we send 'em. Oil cap test, off to get O-ring.

BTW.. this is not only a NA issue. SC models can do the same.

When not properly seated, right beforre a WOT shift...I would get a strange noise. Having just replaced the PCV I removed, inspected and reinstalled properly.