97 Buick LeSabre - loss of power/transmission problems

This is my first post at AF but I've been lurking around for about 2 years and have appreciated the depth of knowledge in the community.

I'm trying to diagnose a problem with my 97 LeSabre. It has just under 98k miles on it. I bought it used at 62k miles 2 and 1/2 years ago.

It ran like a champ until earlier this year when I started to have problems starting it. I don't think that it had ever been tuned up, so I took it to a shop where the plugs and wires were replaced. This shop installed Bosch platinum points, which I've since read are not advised. Can someone explain why this is the case?

Anyway, after the tuneup my wife and were driving back from a weekend trip and lost power climbing a steep grade. The engine was sputtering and we just barely made it back to the city.

Regulars will probably guess that when I took it to the shop and prompted them to look at the intake manifold they determined that it needed to be replaced. (This was not a surprise, as more than one mechanic had recommended that this was needed, but given the history of IM problems with this particular model and year, I held off until the problem manifested itself.)

They replaced the upper intake manifold, but the car still hasn't been 100 percent. It stalls "randomly", seems to not have as much power as before, but the biggest issue is another significant loss of power climibing a steep grade this past Monday. Couldn't get over 50mph and the engine kind of "shuddered" the next 10 miles home.

Did the shop botch the IM work? What gives with the Bosch Platinum points?

Any advice/help would be greatly appreciated.

Sorry for the Russian novel.

Have a compression test and a leak down test done. That should find your problem.

Will do. Thanks for the response.

Will do. Thanks for the response.

I would have a fuel pump test done where they check the pressures while the pump is running. 12 -13 years and 90K miles may have a worn pump. That would especially be likely if the tank level were run low a lot the way that some people try to keep a minimum of gasoline in the tank.

I would suspect the fuel pump not producing enough pressure. Possibly a fuel filter replacement might help.

The Bosch plugs have caused trouble for some people. I'd suggest replacing them with the correct AC Delco plug.

Was the UIM replaced just as a precautionary measure, or was it actually leaking (ingesting) coolant into the manifold?

Coolant had leaked into the manifold.

Over the past 3 days I've noticed a significant loss of coolant (most of the reservoir over 30 miles), but I can't see where it's going. No puddle in the garage, no noticeable leakage on the underside of the car. I've checked the oil and it doesn't appear to be fouled.

Just took it back to the shop and they said an engine check indicated a potential problem with the O2 sensor. This wouldn't, however, explain the loss of coolant.

Any additional advice would be appreciated.

Really good chance the upper intake has ruptured at the EGR port...

If you had the UIM replaced at the shop, apparently the loss of coolant is due to the low level of coolant in the engine. If the coolant was not purged, or completely full after the service, the radiator will suck back coolant from the reservoir until it is full. Just keep an eye on the reservoir and keep it at the recommended level for a week, or so and monitor the change, it should stabilize soon. Once the coolant contaminated the 02 sensor, cat and plugs, it would be best to replace them.