noriceinside

iTrader: (6)

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?

bmccrary

Mine is doing the same, but not quite as bad as yours seems to be. Check your IAC valve. Pull the TB and and clean the sensor and check the resistance between A & B and then C &D. They should be between 40 and 80 ohms. And while the TB is out clean the passage way for it as well. I did the same thing to mine, and it helped some for me, however it didn't do it all.

Also, check your o2's. I wish mine would at least through some codes and let me know there is something going on..

-bryan

onephatZ28

iTrader: (8)

I would look at the fuel pump then the OPTI. it sounds more like a opti

noriceinside

iTrader: (6)

opti? or cap and rotor?

and if it was an o2 sensor wouldnt it be pulling a code for that?


i'll test my IACV but can i do the same to test my crank sensor?

noriceinside

iTrader: (6)

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.

LT1Falcon

iTrader: (3)

i wouldnt worry about the fuel pump, if it can keep up at high speeds it should be able to keep up at adle. I would check opti and O2

FAD2BLK93

have you checked the flow of the injectors themselves? My no. 1...3...5 cly were running so lean they backfired and left no brown residue on the plug. So I took it to the dealer where I work and had them do a top engine fuel injection service and the car runs great. on these cars if one injector goes down the whole bank goes down.

noriceinside

iTrader: (6)

ive done that kind of heavy duty FI service and no change.

noriceinside

iTrader: (6)

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?

noriceinside

iTrader: (6)

k well today i checked the injectors a bit more thoroughly. i read that the resistance should be between 12 and 16 ohms. heres what i got:

1: 13.2 ohms
2: 13.4 ohms
3: 13.1 ohms
4: 13.1 ohms
5: 13.3 ohms
6: 13.2 ohms
7: 13.3 ohms
8: 13.3 ohms

so theyre almost perfect. i am really starting to suspect ignition problem again. i started to suspect O2s, but this feels like its a missed spark, i guess its just a hunch based on how it acts. i think i read another thread where injuneer mentioned that a missed spark wouldnt change the air/fuel mixture, so the oxygen remains in the exhaust and creates voltage in the O2, showing a lean mixture. so that could explain my codes.

i guess all there is to do now is replace my cap/rotor and wires.

Burning Rubber

iTrader: (1)

try changing the ignition module. Its located right on top of the coil. My car had a miss in it and i changed the ignition module and the miss went away. but now its loading up real bad. running extremely rich. i think my injectors are too big.

noriceinside

iTrader: (6)

correct me if im wrong, but the ignition module only controls the timing until the engine reaches 400 RPM. then the PCM takes over.

bmccrary

I thought it was a bit higher than that, considering our cars idle higher than 400. But I am not really sure on that. Officer, what do you have to say on the matter?

-bryan

noriceinside

iTrader: (6)

im almost certain the ICM has no effect once the car is started.

Burning Rubber

iTrader: (1)

i dont know but my car had a bad miss and i replaced the ESC(electronic spark control module) and the knock sensor and it went away

noriceinside

iTrader: (6)

hmm...maybe i should look into those. i do have an LT4 knock module...you think that could be causing timing issues?

noriceinside

iTrader: (6)

i hooked up a snap on scanner to it today and got some numbers. misfire history on #1 was somewhere in the range of 14,000 to 15,000. i looked at that info last year when i was messin with a tech 2 and it was only like 3 or 4...not thousand. only 3 or 4 across all cylinders! the other cylinders were like 50-200 a piece. as it was sitting there idling the current misfires were just going up and up on #1. so i think its safe to say that the problem lies with #1 and the other ones are just due to #1 being so bad (my guess anyway...either that or the cap/rotor are bad).

what really stumps me is my O2 readings. pre-cat O2s were switching from 200ish to 800ish mV like you'd expect, and the post cat on bank 2 did pretty much the same, but the post cat on bank 1 stayed around 80 mV.

to remind you guys, im getting a random misfire code and a lean bank 1 code. occationally i pull a bank 2 lean, but its primarily bank 1. so the post cat sensor is the only one actually reading lean, but how should that pull a lean code and not a insuffient catalyst code?


im so stumped

noriceinside

iTrader: (6)

wow i finally got it. i feel stupid, as most people do when they finally figure it out.

i replaced my EGR valve. it fixed it. i still feel a SLIGHT miss occationally and my idle is a bit bumpy, but then again it always has been. overall the idle is smooth as butter. no more missing at low speed, idle is solid.

apparently the pintle was sticking. i took the valve out and pressed the diaphram back and the pintle would follow until about halfway where it sticks until i jiggle it a bit and it finally drops, so i knew that had to be it.

i guess the egr being open caused the mixture to get screwy, preventing the cylinder from firing properly, resulting in a misfire, then since the oxygen in the mixture remained the same, that resulted in a lean reading. so it all stemmed from the EGR being stuck.