[scartrouble]

I had the lower intake manifold gasket replaced on my 96 Lumina APV 3.4L SFI (116k miles) because the shop said it was leaking antifreeze and I started to note the smell of AF in the car with the heat on. On completion the car backfired and wouldn't run without full throttle - then it would rev high and die. The temp sensor was pegged at full hot. Low fuel pressure was found and the fuel pump replaced.

Starting after pump replacement still extreemly rough - occasional backfire. Extreem low vacuum at low RPM noted. Shop thinks a valve lifter in the wrong hole? Manifold back off to confirm lifters were correct - looks OK. Compression test done while there 5 cyl at 75 and one at 55 ... lazy lifter??

Timing chain estimated to be too loose and may have skipped - possible source of low vacuum. I get it towed home and have replaced timing chain and gears. The original chain had 116k miles and had less then 0.5 inch play and the gears were in the correct position indicating no chain skip. New parts installed and reassembled and I find the camshaft sensor has been plugged into the temp sensor harness and vice versa ... I swap the connectors. Seems to fix backfire and temp gauge reading.

Next start bad idle, surging to almost 2000 rpm when you tap the gas pedal when cold, once hot will idle slow and rough. Engine codes indicate MAF low freq and MAP low input.

Tested IAC - 1.25" to pintle reduced to 1.125".

Found disconnected MAP - connected it. Codes cleared. Still bad idle. Vacuum pressure 4" mercury at idle and MAP not generating an error code. I think it should generate P0107 - does anyone know? I tested the MAP signal voltage 5v at room pressure and 3v with suction.

So I guess ERG - block plate installed - noted back bolt hole stripped. Could be cause of some vacuum loss? Plate seems to make no difference.

All Vacuum hoses from manifold seem OK - still only 4"Hg vacuum at idle.

No code being generated - how can I generate one to ensure ECM/PCM are working?

3 weeks of nights in the garage - I need suggestions!