NoRiceInside

alright let me set it up first. 97 Trans Am, LT1, 6 speed. stock with the exception of K&N FIPK, dynomax bullet, IAT relocate, ported MAF, LT4 KM, TB bypass, CAGS delete, TB airfoil.

now ive got a horrible idle. its pulling codes for random misfire and both banks are getting lean codes. the SES light flashes when i idle sometimes and the idle gets really rough. RPM stays normal but its shaking bad. feathering the clutch is hard cuz if i dont keep the rpm up it bogs. when accelerating or cruising in 1st or 2nd at low speeds (neighborhood speeds) i feel it missing. its got plenty of power (well until today i noticed it lacking) and once i get up to speed its fine.

i was only getting a misfire code so i first suspected tune up as i have 76,000 miles. i changed all 8 with ac delco platinums. no change. soon after i started getting lean codes so i did the fuel filter, no change. then i started to suspect the crank sensor, as there is an oil leak up there and the waterproof seal around the connector is gone. i cleaned it up good, fixed the leak, no change.

i scanned it again today and it still had the P0171 and P0174 lean codes and the P0300 random misfire, but it also had a stored P0400 for EGR flow malfunction. i just replaced that not too long ago, but it makes sense that may be sticking open and that would cause a bad idle, but it wouldnt explain the misfires, and it would be too lean if that was stuck, right?

lately its getting worse and worse. sometimes it feels like its about to stall. would anyone be able to help me out at all?

blackztpi

p0300 is multiple random misfire, as you stated. the ses light will flash if it see's type A faults, which represent hard faults in the emissions or misfire monitors, which is most commonly your crank position sensor for misfires. And, if you CKP (crank pos. sensor) senses consistant multiple misfires, it will throw a p0300 and if it's consistant and bad enough, the pcm will deactivate the EGR system since it doesn't want to recirculate overly rich or lean exhaust gasses. OBD2 is pretty active in protecting itself, so don't be alarmed by seeing many codes. 90% of the time they are all caused by the one related thing.
for a po300, here are some things to look for:
1)make sure your primary side of the ignition is getting full power (12volts.. the primary side is the ignition switch, the battery, input side of the coil, blah blah. secondary side is your distributor, coil, wires, spark plugs, and the output side of the coil)
2) Check all secondary ignition components after eliminating the primary side.
3)check your fuel pressure at the rail, because the pcm can make fuel trim changes to compensate for a lot of things....one of them is NOT fuel pressure. the pcm has no way to monitor or make changes to fuel pressure, therefore it cannot correct a lean condition caused by fuel pressure.

check all of those things and get back to us. it sounds more spark related. see if you can get a scan tool on it to watch and record the monitors as it runs. this would help a lot.

2000GTP

I would also check for any vacuum leaks present and that your IAC valve is functioning properly.

NoRiceInside

ok well i tinkered with it today. fuel pressure at idle is 36 lbs and when i unplug the FPR it goes to 43 lbs. i ran the gauge to my windshield and went for a drive. the pressure stayed good at idle, various throttle positions it did as expected. so its not that. i let the motor run and i unplugged each injector one at a time. each one gave a momentary drop in rpm. so there isnt a bad injector. i checked for spark from the coil. strong spark. i checked a few of the plug wires for spark, really strong, especially #1, which had a misfire code for that cylinder.

i then checked the MAF, IACV, and MAP sensors for anything suspicious, and they all appeared functional and sound. no vacuum leaks were detected anywhere. as i unplugged a few hoses, like the brake booster, the engine stumbled as expected. i checked the EGR. i manually applied it at idle. it stumbled. i checked all other sensors, theyre all plugged in. then i unplugged my crank sensor, and drove it. it still had the idle and miss problem, but it wasnt as severe. also it didnt lack power like it did when it was plugged in. so im leaning toward the crank sensor being bad.

2000GTP

So cylinder one has a misfire present? If so, I would investigate that further. Pull the plug and make sure it is okay and it wouldn't hurt to take the resistance reading on the wire to make sure it isn't grossly off spec. It could also be a possibility that you have a dirty fuel injector. Another easy way of doing it would be to swap things from one cylinder to another and see if the problem follows.

NoRiceInside

well i dont have a p0301 anymore. that was a month ago. since then it just pulls p0300 and p0171 and p0174 codes. the only ones present now are p0335 and p0336 which are crank sensor codes and then a p0400 code. so i just ordered a crank sensor.

2000GTP

I would also check the harness and connector of the crank sensor for damage or corrosion.

NoRiceInside

well for the longest time the weatherproof seal on the crank sensor connector has been missing. so thats why i originally suspected that sensor.

NoRiceInside

ok i replaced my crank sensor today. the idle smooths out quicker and it has a bit more power. but it still misses bad and idles rough. im starting to shift toward O2 sensors?

2000GTP

I would still look into those codes for the lean. I would double check to make sure you have no vacuum leaks and that there are no tears in any part of the intake ducting. I would also check your fuel pressure and make sure it is up to spec. Finally, I would check the MAF sensor and make sure the wire isn't contaminated. If it is dirty, you'll need to clean it. Auto parts stores usually sell special cleaners for the MAF sensors.

LT1_383

I use an electronics cleaner from Radio Shack to clean the MAF wire. Just be careful not to touch it, it's very sensitive and frail.

NoRiceInside

well i checked my entire intake. no tears, no vacuum leaks. its good. i cleaned the MAF and throttle body with some carb cleaner. its all good.

only thing im suspicious of is my AIR tubing is torn. its before the check valve. so it shouldnt cause an exhaust leak. and its not that bad. i can fix it and the problem is still there.

NoRiceInside

it almost feels like the EGR is open. but i dont think that would cause the kind of miss feeling i get at low speed, and if the EGR is stuck open it should be rich, not lean. right?

Injuneer

Not correct. It can't change the fuel pressure, but it can change the long term fuel corrections to change the pulse widths, and supply more fuel at the lower pressure. The end result would be increasing BLM's, and when they approach the limits, you get the "lean" codes for long term fuel corrections exceding the threshhold.

NoRiceInside

...