Need heip!

[lsruthles]

So i bought my first LS1 about a year ago, a 98' Z-28 with 190,000 miles. Didnt run when i got it, but put a new fuel pump in it and it ran like a champ. Got the car in louisiana then moved back to montana two months later. The first time it hit below sixty degrees the car idled like crap till it warmed up. Surging from 500 rpm to 2500 rpm and back down, sometimes to a stall. Checked everything I thought it could be, and every idea I got from reading the threads here. I even did most of the free-mods suggested. Got the codes read for me at an autozone and they said the upstream O2 sensors were bad. replaced them with new sensors but no change. The car has progressively run worse up to now, but now when I step on the gas, it dogs out until I stomp it, or get up to speed, then starts all over again at the next stop, but runs fine when up to speed or really on the gas. New fuel filter, plugs, wires, cleaned MAF, New air filter, checked IAC for proper operation, and everything else I could think of over the past 6 months. Monetarally challenged at present so any advice would be GREATLY appreciated. Thanks all and I love this website!!

[SMWS6TA]

more info....why was it not running when you got it? Did the previous owner tell why? Some history about the car. Is it a Katrina Flood car. It being from LA I wouldn't doubt it. If so, you could have water damage with the electronics and PCM.

Have you checked the fuel pressure at the rails? Should read about 50 psi at idle. Fuel lines could get clogged with a bad pump. Did you just change the fuel pump or did you do the regulator too? OEM pump or another brand?
.
Also have you check the IAT (Intake Air) sensor and MAF are working correctly. Disconnect the MAF harness, it will go into Density tune tables. See if that runs differently. If it idles a little better then your MAF is done.

[KMdef9]

How did you check the IAC?

A sensor can be bad even though IRS clean too.

[lsruthles]

more info....why was it not running when you got it? Did the previous owner tell why? Some history about the car. Is it a Katrina Flood car. It being from LA I wouldn't doubt it. If so, you could have water damage with the electronics and PCM.

Have you checked the fuel pressure at the rails? Should read about 50 psi at idle. Fuel lines could get clogged with a bad pump. Did you just change the fuel pump or did you do the regulator too? OEM pump or another brand?
.
Also have you check the IAT (Intake Air) sensor and MAF are working correctly. Disconnect the MAF harness, it will go into Density tune tables. See if that runs differently. If it idles a little better then your MAF is done.

Car was not running because oem pump was putting out 18psi at the rails. I put a walbro 255 in it and it ran great w/ 56psi at rails now. Was from inland louisiana so not a flood car, no signs of it anyway. IAT sensor may be bad, but i dont know how to test it. MAF sensor could be a problem, but it runs close to the same plugged in or not. I removed the IAC motor and turned the car on to check if the plunger worked or not, it definitely moved in and out so I just assumed it was in working order. thank you guys for your input, anything helps.

[0rion]

is your coolant temp gauge looking normal? Usually the symptoms will be exactly opposite of what your'e describing if a temp sensor is bad but could be worth a check.

[pajeff02]

Vacuum leak might also be an issue.

[cammed goat]

Spray around the intake manifold with brake cleaner to see if the idle rises. If it does, you have a vac leak. I can't recall F-bodies very well, but check the driver side cylinder head toward the front of the car and see if you have a broken coolant temp sensor.