[Karston98GTvert]

My car keeps throwing the code 'P0135 and P0155'.
'O2 Sensor Heater Circuit malfunction'

So that means both of my front o2 sensors are having problems.

I replaced ALL 4 02 sensors (front/rear) tonight, and nothing changed.

First start up when engine is cold: idles fine with no misfires.

after warmed up, under med-high throttle: misfires constantly.

after warmed up, under very light throttle: drives fine.

after warmed up, at idle: misfires every couple of seconds.

Someone PLEASE help me! My parents are pissed at me because they think i fuc*ed the car up, i'm pissed because they're pissed, and i'm also pissed because i cant drive my car.

['97'Cobra]

first check to make sure the O2 wiring harness isnt burnt, freyed from the hot exhaust. If everything checkes out look at the connectors for bent pins or corrosion. If that looks good pull the plugs and check them along with your wires. Plugs and wires would be my next step possibly the cats could be clogged.

[96-GT_Josh]

Heh, sounds like my stang. I don't know how many o2 sensors I replaced untill I said F it and just went O/R H and got the rear ones tuned out.

But yeah I had the same issues, Car ran fine cold. But as soon as it heated up it would stumble/misfire at 3/4 throttle or just cruising at say 45 in 4th pretty bad too.

And sitting at a drive through and having the car idle down to about 3-400 rpm and feel like it was going to die then it would jump to 8-900 rpm for about 5 seconds then misfire its way all the way back down to 3-400 rpm and repeat. Eventually it burnt the cats up and clogged them soo bad the car wouldn't go over like 20mph. Thats when I went to an exhaust shop I used to work at and had a custom O/R H made up for free and then to my buddys shop to have the tune.

EDIT: Btw good luck because mine never got fixed. I replace Coolant temp sensors, plugs, wires, coils, PCV, vacuum lines, EGR Valve, 3 MAF sensors, IAT sensors or whatever the little one on the intake is, TPS, Cleaned the TB, Checked Comp, oil coolant new Water pump, hoses, thermostat, & alternators (different problem there) Fuel pump, fuel filter, FPR, fuel relay and every fuse inthe car and nothing fixed it.

But as soon as I had the exhaust work done. No problems. Even for the week that I drove it with no tune or cats. It smoked a little on cold starts but no misfires. Hmmm. Just runs smoother now with the tune.

[1996 GT]

Plugs pop easy out of these cars. See if they're loose. Coil packs could be on their was out, do you know what cylinders are miss firing? What are your mods?

[Karston98GTvert]

I have an o/r x with flowmaster 44's... Should i try MIL eliminators? I don't have them because when i cut the cats out (was originally a catted x) the engine light never came on.
All this is happening after i replaced the intake manifold gasket... Thats why i'm so confused as to why this is even happening.

My friend has MIL eliminators, I'll plug his in to see if it fixes the problem.

Thanks for your guys' help. Much appreciated.

[Islandvobra]

When you changed your intake manifold gasket did you unplug any wire harnesses? Check the Wire harness to the transmission and see if it is plugged in properly. Do your backup lights work properly? Speedo work ok? These are all on the same harness.

James

[Karston98GTvert]

Yes my backup lights and speedo work fine.

But, my oil pressure gauge is stuck at 'L' I'm pretty sure i have oil pressure because i'm not having any metal/metal noises coming from the engine so i'm not too worried about it. I am low on oil so i'll see if adding more will fix that, I'm not driving the car at all until i get everything fixed.

[Islandvobra]

I assume you have checked all the fuses in the car?

[Karston98GTvert]

Yes i have. both ends of all of them show 11.9-12.2 volts on both ends.

[whiteout34]

new spark plugs and spark plug wires as another step.... and check ur connections for ur o2 sensors.... check ur firing order...

[96red&blackstang]

for some reason this sounds like my car.... :/ My check engine was always on, but after a month after getting my o/r xpipe it turned off. yet, i feel like it has trouble because it smoking alot at idle. might check the O2 on the car to see if anithing happens. hate having to stop at a red light and see all this smoke come out.

[jme30426]

Have you checked if your gaskets on intake are not leaking. Bad air fuel mix will make it do all that stuff too