Recently changed the lower intake gasket on my 96 Series 2 3800. [non supercharged] While I was at it I installed a new upper intake. I was experiencing some unexplained coolant losses, which now seemed to be fixed.

However, after completing all of this work, I now have a slight hesitation, a slightly rough idle, and some shuddering in overdrive, none of which were present before the work was done. :? [At least not that I recall]

I took it to my local mechanic, he did code test on it, [the engine light was flashing if you pushed on the accelerator too much] and the 02 sensor showed it was very slow in responding. He thinks the previous coolant loss [lower intake gasket was pathetic] has ruined the sensor...?

He also found 2 less than perfect ignition wires. He suggested replacing all the wires and plugs, a new 02 sensor, and having the injectors flushed.

I replaced all the wires and plugs, and it seems slightly better, but still far from perfect. Three of the plugs were "white" instead of grey. Would cleaning the injectors and changing the 02 sensor help any further?

I’m wondering about a slight vacuum leak :? , but have not been able to find one in any of the lines, or by spraying break cleaner all around the lower intake and the injectors.

Any ideas guys?

Thanks!

Check for leaks where the upper manifold bolts to the lower. If they aren't all tight the way they should be and can cause a rough idle condition also. And changing the O2 sensor probably isn't a bad idea, as coolant isn't too good for them.

Make sure you reinstalled the o-rings around the PCV (they slip into the UIM, PCV housing). If the o-rings are missing and/or the PCV is bad (shake it to see if it rattles, if it does, then it'* good) then you will get a rough idle.

Thanks for the suggestions guys!

The upper intake bolts are tight. [I double checked them] The PCV valve is good, [it rattles] and the 0-ring is there.

Any other ideas?

Thanks

what about the o2 sensor???

I wondered about that too...

But then why didn’t I have these issues before the work was done on it? Does it make sense that the 02 sensor would suddenly cause these issues immediately after the gasket and the UI were changed? :?

Thanks

did you burn off a lot of coolant after you replaced it? i think that would possibly foul an o2 sensor...although i burned off a ton, and still had a little white smoke after itd been running for 5-10 minutes, and to my knowledge my O2 sensor is fine, at least its not throwing any codes, im getting about 20mpg at best, but i think thats due to my foot more than anything.

Coolant will kill an O2 over time.

Forget the injector flush. I seriously doubt that will do anything for you. A vacuum leak would be far more likely.

My mechanic still says it could be an injector...... He suggested that when I had it apart a tiny spec of dirt may have entered somewhere in the system, and now its not functioning properly....

Can the injectors be cleaned one at a time off of the car somehow? Compressed air perhaps?

Thanks

Ok...Finally found the problem A bad ignition coil on #3 cylinder. Its running much better now with a new coil installed.!

Now with the LIM gasket leak all fixed, the coolant pressure is back up to where it should be, and now my water pump is leaking... Hopefully once I replace that, everything should be good for a while.