Hello everyone. I've just rebuilt my '89 Iroc's 305 TPI engine (my first, with help from a much more knowledgable friend). Everything on it is stock with the exception of headers, high output oil pump, hyptertech stage 2 prom & thermostat. It's been through the breakin period with the first oil change, and final valve readjustments (hydraulic lifters). The problem I'm having is twofold. First, sitting at a light idle in gear, with foot on brake (auto tranny), the idle will pickup, then drop off, then pick up again over and over between a range of about 1000 rpm (not sure the exact RPM's as the tach is off. We set the idle at ~850 via a diagnostic computer). Occasionally, it will iron itself out and idle fine, but more often than not it will keep it up.
Second, while cruising at any speed the engine will start surging. If I give it gas it stops. If I let up on the gas it stops. If I'm giving it just enough to keep a constant speed, it'll start surging again. This seems to be an intermittant problem, but it's been happening more often.
A little more history - the computer is coding with a 'engine running lean' code a few times a day. During the rebuild, I replaced the O2 sensor with a new one, didn't secure the wire and it ended up melting against the header and shorting out. Replaced the O2 sensor *again* with a new one. Installed a new fuel filter. Gas mileage went up from ~8 mpg to ~13 mpg. Used to get ~20 mpg before the rebuild.
It's been suggested to me that the computer may have been fried by the O2 sensor shortout. Any other ideas?
Car Details:
'89 Iroc Convertable, 305 TPI (F Code), aftermarket headers & muffler, Hyptertech Stage 2 PROM. Had block & heads baked and checked out & had valve job done as well as having injectors cleaned. Replaced the following parts with new ones throughout rebuild: All gaskets (of course!), cam & lifters, bearings, oil pump, fuel filter, O2 Sensor, piston rings, plugs, wires, cap, rotor, radiator, B&M transmission shift kit (700R4), shifter cable, transmission mount, battery.
[This message has been edited by miroc89 (edited 10-21-2000).]
Second, while cruising at any speed the engine will start surging. If I give it gas it stops. If I let up on the gas it stops. If I'm giving it just enough to keep a constant speed, it'll start surging again. This seems to be an intermittant problem, but it's been happening more often.
A little more history - the computer is coding with a 'engine running lean' code a few times a day. During the rebuild, I replaced the O2 sensor with a new one, didn't secure the wire and it ended up melting against the header and shorting out. Replaced the O2 sensor *again* with a new one. Installed a new fuel filter. Gas mileage went up from ~8 mpg to ~13 mpg. Used to get ~20 mpg before the rebuild.
It's been suggested to me that the computer may have been fried by the O2 sensor shortout. Any other ideas?
Car Details:
'89 Iroc Convertable, 305 TPI (F Code), aftermarket headers & muffler, Hyptertech Stage 2 PROM. Had block & heads baked and checked out & had valve job done as well as having injectors cleaned. Replaced the following parts with new ones throughout rebuild: All gaskets (of course!), cam & lifters, bearings, oil pump, fuel filter, O2 Sensor, piston rings, plugs, wires, cap, rotor, radiator, B&M transmission shift kit (700R4), shifter cable, transmission mount, battery.
[This message has been edited by miroc89 (edited 10-21-2000).]