Can't figure out what to do next

**f16z28** · 01-19-2008, 06:13 PM

This has happened twice to me now. When i pull up to a stop light the rpms get very low around 300 and the engine stumbles and shakes the car like it is about to die and then recovers as though nothing happened. Also I noticed when i accelerate from a stop that it hesitates a little to start then is fine. i have no other problems. I got an auto tap and had the lean codes on both banks. i have installed the slp cold air kit, slp maf, slp throttle body, slp thermostat, slp smooth air bellow, msd wires, bosch platinum plugs, slp loudmouth exhaust, 3'' y pipe, edelbrock shorty headers w/jet hot coating and an arp underdrive pulley. i installed all of those mods about 30k miles ago and never had a problem. the car currently has 112,000 miles on it. i am also trying to sell it so i dont want to spend alot of money. any ideas?

**Justin23454** · 01-19-2008, 06:22 PM

ive got the same problem.... I dont know what it is.... I wold like to know also. I dont know if yours does this, but when I push the gas down easy, sometimes it stutters? I dunno whats up.

**Wesman** · 01-19-2008, 06:57 PM

Is the car an automatic?? Almost sounds like the symptoms of a bad torque converter lockup solenoid. When the car comes to a stop, the TC is supposed to unlock before the RPM's drop below idle. If the solenoid goes bad, it can cause the car to stall, or in your case drop the RPM's low enough to almost stall. Sounds like its not unlocking at the proper time, and lugging the motor as the car sows down.

The way to diagnose the issue is to shift the transmission into neutral before the car comes to a complete stop. If the issue goes away, then that is most likely your problem.

**Tracker9118** · 01-19-2008, 07:00 PM

Look at the plugs may need new ones.

**Tracker9118** · 01-19-2008, 07:04 PM

Unless you have let the car go for a long time can be just bad gas.
93 or more i had bad gas at BP or SHELL.

**Tracker9118** · 01-19-2008, 07:08 PM

Or your PCM is taking a shit on you i put a new one in mine bout 6mo ago.
GM did have a recall on them bout 8mo back it was for 3 years i no 99.

**02blkws6** · 01-19-2008, 07:15 PM

Ever think about the SLP MAF. Try a stock MAF and see if there are improvements.

**Tracker9118** · 01-19-2008, 07:26 PM

The car service light on???? may need to plug into it.
I have all of GMs F-body books for 1999.

**Tracker9118** · 01-19-2008, 07:50 PM

If it is the mass air flow the trouble code.
system Performance code-P0101
Circuit Low Frequency code-P0102
Circuit High Frequency code-P0103

**f16z28** · 01-19-2008, 11:26 PM

well its only happened twice so its hard to diagnose when i have a line of cars behind me when the light turns green. Yes it is an automatic. and about 60,000 miles ago i got a whole new transmission installed under warranty at a gm dealer. i looked at the maf screen and it looks pretty clean. This problem came about rather quickly and wasnt something that has been getting gradually worse. I'll start putting 91 oct in it next time i fill up, along with some fuel treatment. i'll probably replace the fuel filter also and see what happens. I'll post again sunday after i do all this and we'll see what we get. i will also pick up an obdII reader and clear the codes afterwards. last time i cleared it was the lean left and right bank codes.

**f16z28** · 01-19-2008, 11:29 PM

i will also pick up an obdII reader and clear the codes afterwards. last time i cleared it was the lean left and right bank codes.

**INMY01TA** · 01-20-2008, 05:53 AM

Sounds like what happens when the car has to re-learn the idle procedure, like after having the battery unplugged.

**Wheeler99WS6** · 01-20-2008, 06:13 AM

Originally Posted by f16z28

i will also pick up an obdII reader and clear the codes afterwards. last time i cleared it was the lean left and right bank codes.

the maf is probably giving you the lean codes, I had a Gmaf for a brief period, it gave me lean codes so I tossed it and put the stocker back in and no more codes.

**Tracker9118** · 01-20-2008, 06:20 AM

You may want to try a good fuel additive like NOS OCTANE BOOSTER RACING FORMULA if you have a fuel prob, it will also clean out your O-2 sensors all 4.
I use it and i am happy with it my LS1 seems to love it.
Will not harm O-2s or your cats if your still running them.
Or you may have an O-2 going bad.
That prob, is a little odd the only thing i had to do to mine is get a new PCM 6mo ago & i have 106698 mi on it.

**f16z28** · 01-20-2008, 10:32 AM

Originally Posted by INMY01TA

Sounds like what happens when the car has to re-learn the idle procedure, like after having the battery unplugged.

Originally Posted by Wheeler99WS6

the maf is probably giving you the lean codes, I had a Gmaf for a brief period, it gave me lean codes so I tossed it and put the stocker back in and no more codes.

I can't remember the last time i unplugged the battery so i dont think thats it. do you really think it would be the maf? why would i have it in for over 50,000 miles and all of the sudden it goes bad? shouldn't i have gotten codes right after i put it in?

**f16z28** · 01-20-2008, 11:11 AM

im going to auto zone right now for the nos octane booster, a fuel filter and my gas tank is low so im also going to fill her up with 91 octane. i used to use 91 all the time and switched to 87 about a year or six months ago.

**INMY01TA** · 01-20-2008, 12:27 PM

I would put the stock maf back on. I had a GMAF back in the day, worked for like 6 months then started running like shit. Put the stocker back on, no more problems.

**Wheeler99WS6** · 01-20-2008, 01:04 PM

Originally Posted by INMY01TA

I would put the stock maf back on. I had a GMAF back in the day, worked for like 6 months then started running like shit. Put the stocker back on, no more problems.

Same here....it worked fine for a while but after about 8 mos it crapped on me. I actually had no problems out of it until i installed my LT's and true duals. Pissed me off enough to pitch it and put the stocker back on.

**Frost** · 01-20-2008, 02:18 PM

lean codes are commonly stopped up fuel filters or weak pumps. Get a cheap guage and check the pressure at the rail. Should be 57-59psi. if it has enough lead, tape it to the windshield so you can see it and drive, see if the pressure falls under load.

A dead miss or misfiring plug can set the sode too; misfires force fresh unburned oxygen out of the chamber and intot he exhaust. The O2 will only read it as lean from the high O2 content.

**f16z28** · 01-20-2008, 08:53 PM

Originally Posted by Frost

lean codes are commonly stopped up fuel filters or weak pumps. Get a cheap guage and check the pressure at the rail. Should be 57-59psi. if it has enough lead, tape it to the windshield so you can see it and drive, see if the pressure falls under load.

A dead miss or misfiring plug can set the sode too; misfires force fresh unburned oxygen out of the chamber and intot he exhaust. The O2 will only read it as lean from the high O2 content.

what kind of gauge do i need and where can i get one? I fillued up with 91 octane and replaced the filter toningt but only started it in the garage. i didn't take it out, so im sure the 91 octane gas didnt make it all the way to the engine just yet. i have the nos octane booster which i will add tommorow.