Car is an 85 Z28, 305 TPI, 700R4. Fairly stock, Mild port+polish on heads when a valve job was done. Electric fans on a switch and 160 degree T-stat. Smog deleted and gutted cat. Just bought the car a few weeks ago, been sitting for a few years due to needing a new fuel pump. Got the car, put in fuel pump and ran fine. Few days later after sitting, wouldnt idle but cleared up in a few seconds, no other symptoms. Driving the car the other day through the city, car was idling very low and would stall in gear at stoplights. Was able to limp home with no CEL. Cleaned MAF, New plugs, etc, etc. Now the car seems to have a mind of its own. Fires right up sometimes, idles fine and goes into gear idling fine. Other times it will fire right up and need some help to stay running but no problems other then that. Then other times it will barely idle, pumping it doesnt help at all, and it backfires through the intake. I'm lost, every time i try to chase the problem, its gone. Any help would be appreciated. Thanks guys

 

have you replaced the fuel filter? and do you know who did the work on the heads...back firing thru the intake sounds like a problem in the head to me

 

i would try to do a compression test on all cylinders to look for leaking/sticking valves

code 33: im not sure what that is i dont think its even in my GM service manual

34: is the MAF which you said you cleaned...are the sreens still on it? not ripped or anything? it may need to be replaced

 

Would a leakdown test be more in order? Compressions just going to give me Cyl pressure. 33 Is High voltage, Low vaccum at MAF, 34 is Low Voltage, High vaccum at MAF? Which seems odd both these would cccur at the same time.

 

Previous owner. Very mild and done over 70000 miles ago.

 

yea you would get better information doing a leak down test.

as for both high and low voltage i honestly dont about that i have never been in that situation before

 

I plan to pull the valve covers tomorrow and check the rods and valves. I'm thinking its something computerized though, because the backfiring isnt constant. one minute i can drive the car without problems. Shut it off, and it runs like crap.

 

Cleaned IAC, doesnt idle great but stays running on its own. backfiring out the exhaust now.

 

Now i have code 22, Low voltage at TPS. What now?