Low vacuum 1996 3.4l

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!

..so to sum it up, high cold idle speed, rough idle after that, poor vacuum at idle.
since you have done all one could normally think of, only comment is high idle has been reported by others as related to vacuum loss...so it figures.
IN regard to testing ECM, I think if you electrically disconnect EGR valve , it will throw a code...at least mine does so...
....what method do you use to measure vacuum? External tester or existing MAP ?

Disconnected EGR and generated a code going to work today - don't know what it is yet.

Low vacuum measured with vacuum gauge connected to MAP line.

Also noted today there is no surge after warm up - does this mean IAC valve is OK?. Rough operation (like timing is off) extends into higher rpm above low idle, but I have no tack, so I can not give accurate number. I guess 300-500 rpm (before the engine whine exceeds the rough noise) I can still hear the cylinders popping slighlty.

So the codes generated were EGR, MAP low and MAP high (with a new replacement MAP installed).

After clearing codes and plugging in the EGR, no codes, but still extreem low manifold vacuum (4") and rough idle. Surge on warm up, but just rough when warm.

I checked the coil/plug order ... that is not it.

Can anyone tell me if the MAP sensor should generate an error due to this low ammount of vacuum?

Can some one tell me how to find a vacuum leak at low RPM? I have uut a cork in the PCV line at the intake, plugged the brake boost line and Aux vac line, checked the EESC (near 0" vacuum - not sure if this is normal?). All vacuum line tests checked individually - not at once ... I looked at the tranny line too but it is metal and looked OK ...

Someone throw me a bone please ...

1996 3.4L SFI:

engin rough idle - low intake manifold pressure (4"):
questions
1) I disconnected the crankcase position sensor and started the engine. Runs smoother, but stalls out. Does not generate error code. Should it run? Should it generate a code?
2) I disconnected the camshaft position sensor and started the engine. No change. No code. Should it generate a code?
3) At idle with only 4" Hg vacuum, should the MAP generate an error?

CKP sensor did generate error starting car a second time when disconnected.

Error cleared. Plugged back in. Same condition. Off disconnected CPS and ran for a while ... no code still.

What does it take to generate a CPS code?

CPS power 11v
Reconnected

signal test seems odd ... process is disconnect all plugs and crank to look for 10v pulse
Results
When ignition goes to ON the signal is always 10v. During cranking seems to be 0 and bumps to 1 (suspect this is meter response - I do not have an oscilascope). Then stop cranking to ignition ON and the signal votage returns to 10v.

I would think the initial signal voltage would be 0 and only hit 10 as TDC for c1 passes ... the odds of me stopping cranking each time at TDC for c1 seem low

Any one know more about this?

*I am closing this thread for lack of activity it can be picked up in the Lumina car forum. Also Forum rules do no permit duplicate posts.