Thread: Installed New Transmission Now Won't Idle in Park or Neutral. P0171 and P0306 Codes

Hello,

2002 GTP - Stock

I pulled the engine and installed a new transmission last week. Everything went back together great but now the car won't idle in Park or Neutral when warm. The idle bounces from nearly stalling to 1500 RPM or so and is really rich smelling. It's throwing P0171 and sometimes P0306. It idles fine at first start up, and in gear, and it ran well before I took everything apart. no issues(aside from the blown up trans).

When I pulled the engine/trans I only disconnected the fuel rail, harness, TB, and a couple vacuum lines. I didn't disturb the top end of the engine or supercharger at all. I also swapped over the old NSS and speed sensor to the new trans.


I've checked all the vacuum lines/connections
I've checked all electrical connections
I've pulled the fuel rail and cleaned up the ports

Where do I go next in the troubleshooting? I really don't want to start throwing a ton of parts at it...


Thanks!

Almost sounds like a vacuum leak. Did you install new injector O-rings when you pulled the rail? I know you said you checked all the vac. lines but did you check the "T" under the S/C snout? It gets broken often and can cause issues.

Well... I replaced the O-rings on the injectors and replaced a lot of the vacuum lines/fittings. I'm now getting an intermittent P0131 and still have the surging idle in P and N. I tried unplugging the mass air flow sensor and the idle evened out in default mode. What does that tell me? replace the O2 sensor, or the MAF. or both??

I replaced the o-rings on the injectors and injector #6, and i also replaced many of the vacuum lines/fittings for good measure. I don't think any of them were leaking, but they were old... It runs awesome now when cold I'm now throwing an intermittent P0131 "O2 low volt B1S1" and P0133 "O2 slow response B1S1" and it is still surging at idle in P and N at operating temp, though. I didn't have a lot of time tonight, but i did unplug the MAF when it was surging and the idle smoothed out on the default. I didn't think to unplug the O2 sensor to see if it does the same thing, but I'm pretty sure O2 sensor #1 is bad. Do you guys think maybe the MAF is bad too? I have the BlueDriver Scanner so I can log data. What should I look for?

Thanks!

Dumb question but have you checked to see if the MAF fuse is blown? Besides that, maybe give it a good cleaning with MAF cleaner (not brake clean).

Also, check to be sure that #4 and #6 spark plug wires aren't touching the upstream O2 sensor. And no need to disconnect it unless you suspect it's not making a good connection in the plug.

Here is some info on the P0131 code:

P0131
Trouble Code Conditions:

DTC P0101-P0103, P0106-P0108, P0112-P0113, P0116-P0118, P0121-P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449 and P1441 not set, engine started, TP angle from 5-40%, and the PCM detected the HO2S signal was less than 175 mv for 45 seconds, or less than 600 mv for 55 seconds while operating in P/E mode during the test. The HO2S is used for fuel control and post-catalyst monitoring. This sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. At initial startup, the PCM operates in open loop mode, ignoring the HO2S signal when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference (or bias) voltage of about 450 mv. The HO2S generates a voltage within a range of 0-1000 mv that fluctuates above and below the bias voltage once in closed loop. A high HO2S voltage indicates a rich fuel mixture. A low HO2S voltage indicates a lean mixture. Heating elements in the HO2S shorten the time required for the sensor to reach normal temperature, and an accurate voltage signal.

Possible Causes:

• Air leaks in the exhaust system, intake manifold, vacuum lines
• Engine misfire condition present (look for P0300 series codes)
• Fuel system too lean (possible low fuel pressure, water in fuel)
• HO2S signal circuit is shorted to the sensor or chassis ground
• HO2S is damaged (i.e., cracked) or air reference hole clogged
• PCM has failed

Bad oxygen sensor, bad connection is normally the only cause for those codes... I can unplug 1 injector and the o2 still fluctuates nicely, like you would need 3 cylendars not getting fuel and just pumping air to get a working o2 to sit low that long... If your fuel trims are positive to the max, watch them and your o2 sensor while you inject propane into the intake.. if the positive trims start coming down then you know the o2 is prolly good.. I use a propane torch with a hose pushed over the end and tape off the air ports on the torch so no air can get mixed with the propane and put the hose in your intake .. you can also move the hose around the manifolds to find vacuum leaks

Personally though, it sounds to me like cyl#6 is just pumping air and not getting any fuel... So disconnect the plug from cyl#6 and check for power, or plug a node light in and see if it flashes while the motor is running.. if the electrical tests pan out then replace the injector for cyl 6... If you have a lean code and misfire then it's NOT an ignition problem it's a fuel problem and since the motor runs its most likely a bad injector or the injector isn't getting power. So check all the plugs the injector wires go thru..