iverson387

Car is a 98 trans am with forged 347 tsp stg 2.5 5.3l heads, ls6 intake, granatelli maf, and torquer v3 cam. Now the car was recently tuned by a reputable shop but had a problem where it surged at an idle and would sometimes die. Driving it home got a code for insufficient switching 02s. Put a new pair of gm o2s in it and now it idles perfect in closed loop but in open loop it surges. I was told its prob an intake manifold leak by the tuners buy after changing the 02s it is now intermittent and is fine 95 percent of the time so i dont think theres a leak. I looked everything over took off manifold to be sure and everything looks like it is sealing ok. The car is not throwing any codes anymore and normally only does it on first start up in open loop. But the thing is it doesnt do it every time and is random. Any suggestions? Maf?

98Aggie

iTrader: (19)

Your tuner needs to spend some time with your VE tables and desired airflow tables. The reason it idles fine in closed loop because you are using all the engines sensors to make corrections. In open loop you rely on the tables set by the factory or any changes made by your tuner.

TPI TERROR

iTrader: (52)

Similar problem as the OP with my build, stock internal mild heads and cam, full bolt ons. Car made 395 rwhp 395 tq. The car surges and doesn’t respond immediately after being turned on. It is worst under low RPM’s but if I get on the gas there is a hesitation, then all of a sudden it jolts and runs fine.

I had a code for a bad 02 sensor so I replaced and cleared the codes. Unfortunately it’s still surging upon start up. I’m suspecting it might be my Granatelli MAF that the OP and I have in common. I ruled out a vacuum leak because it runs fine in closed loop.

Any other ideas?