The Nissan Path

Having problems with my 2003 3.5L pathfinder. Has following symptoms:
OBD Codes: P1217 Manf control Fuel Air metering - displayed twice once with the P1217 code and once with P1217p/d - whatever that means. Also has Catt eff below threshold P0420.

Starts fine but after it warms up the RPM's become erratic and the engine temperature starts to swing wildly - both at the same time, with the temperature often pegging high. On stopping the car and inspecting, I do not believe the high temperature is real - no smoking or coolant relief, doesn't smell or sound hot. Really appreciate any help.

One other symptom is that the car seems to actually run/accelerate better than normal until it warms up - very strange. Car has 210K and has been running great otherwise.

The P0420 is a catalyst efficiency code, detected when the ECM does see a significant differance in the rich/lean cycling between the front and rear O2 sensors. It often indicates that the catalytic converter between those two sensors is in need of replacement. Since you have another issue, I would concentrate on that and correct it, erase the stored codes and wait to see if the P0420 code returns.

P1217 is a manufacturer's code meaning the ECM has detected the engine is over temperature. Since you don't think the engine is actually overheating, I would want to see what the engine coolant temp sensor is showing on a scantool when this occurs. If it showed a ridiculously high temperature (ie 400 degrees F.), I would suspect a circuit issue or bad ECT sensor. This code usually occurs when (1) the coolant system was serviced and run low and refilled and air pocket(s) exist in the coolant system, (2) when the crank driven cooling fan is not working properly (usually a bad fan clutch) or (3) or when the electric cooling fan, if equipped, doesn't work properly. In general, anything that can cause the engine to overheat can cause this code to occur, including bad thermostat, water pump, radiator and/or cap, etc.

All that said, if it were mine and I really felt that the engine wasn't overheating (an infrared temp detector would come in handy here), I would concentrate on the ECT sensor and circuit first.

I actually bought a new temp sensor but was thinking it had to be some other problem as the rpm and the temperature fluctuations were almost synchronized - but I guess if the Temp sensor flakes out , the ECM would be affected and could alter the Fuel/air mixture and result in the cat error code as well. To be honest the other reason I didn't go ahead and replace it is that I couldn't locate it. I did read some posts that you have to removed the intake manifold - so I really wanted to be more confident that was the problem.

I don't have an IR temp scantool - but I have seen overheated engines before - usually there is some smoking of residual surface engine oil deposits and "crackling" of the exhaust system - none of which were present.

Yeah, you need to remove the intake manifold to get to it. You might be able to see the harness for it if you look near the AT dipstick. That's why I would use a scantool to see what it's reading. Some problems are hard to diagnose without a good scantool, these days!

Thanks for the suggestions - but currently the problem has gone away. I actually do have a scantool - thought you were talking about an IR temp scanner - forgot the code reader also displays data including coolant temperature.

Anyway I went ahead and reset the codes and connected a scanner to watch the actual coolant temperature while I drove and after 20 miles - nothing. The coolant temp lined out around 185 and no power/RPM drops.

Thinking it may possibly have been a sensor short - the car had set for 12 days and we had a lot of rain - perhaps after I drove it, the connection/short dried out. A friend said he had a Jetta with a crank sensor sensor short which drew down power to the ECM connected sensors and resulted in all sorts of false errors/indications. Really just guessing until it happens again. Thanks a lot for your help and will let you know how things go.

Might want to try monitoring the ECT while wiggling the ECT harness.