1994 GP SE Knock Knocks like a joke when idling

[robertrod]

Ok, 94 GP SE with 155k mi has been knocking.

When inside the vehicle after a cold start, the knocking is a muffled tap tap sound, and a slight vibration can be felt in the floor. However, when the hood is up and I'm standing in front of the car the knock sounds like something is whacking the engine with a hammer from the inside.

I only notice this while idling in the morning or when first started. The engine sounds rough in general and eats about a quart of oil a month.

I bough a new EGR valve last week and put it in because I had a CEL that read out EGR solenoid. Does this have anything to do with the knocking and rouch running?

 

[torq455]

Do you have a good level and clean oil, the right viscosity, does the knock go away after it warms up, are you losing coolant, when was the last time you had a tune up and fuel system cleaning, and how oil coated is the engine? The 3x00's have a very leaky lower intake manifold gasket. That era, it was normal to replace them every 40K to 80K miles. My 97 Lumina 3100, same miles, did the same thing. Nearly sounded like a diesel. After 5 minutes or so, the knocking went away. I understand it to be a little too much clearance in the wrist pin/piston assembly. When it gets heat in there, things swell up and get tighter. GM claims that's "normal" as long as the knocking goes away after 20 minutes. Otherwise, the engine gets replaced.

 

[robertrod]

Well, the oil was changed about 1500 miles ago, added about 2 quarts since then - 'high mileage' 10w-30. The knock disappears about 5-10 mins after startup. Coolant loss is about 1/2 inch in the tank every 8 months. I use Lucas fuel system cleaner every 6 months or so.

The other day I was driving on the highway and it starting shaking and hesitating very badly. Lately the throttle response on the highway was next to nothing after 60mph.

I took it to my mechanic that night and he said the valves were not seating properly. He took some reading and told me the compression in the head was 1/2 of what it should be. In addition he thinks the knocking could either be a rod or the flywheel.

Codes:
28 trans range switch
23 intake air temp low
43 esc module
77, 76, 75 egr solenoid 3, 2, 1

So on a car with a low resale anyway and looking at possible motor replacement, I told him to put it back together. I think I will sell it for parts or for someone who wants to fix the motor.