The NT started getting intermittent MIL's about 2 1/2 months ago. Interestingly, the problems started 3 weeks after dropping the NT after hitting a deer. I'm crossing my fingers that it is now cured, or at least in remission.
Symptoms: A solid MIL lit when ignition key turned to start. Most times it would clear by cycling the ignition switch, on a few occasions the MIL stayed solid. Could also clear MIL by cycling engine kill switch. Active MIL's were always an ECM code 1- Manifold Absolute Pressure (MAP). Stored codes in the ECM were always (and only) a 1, MAP voltage, hi or lo.
A few weeks ago the NT started stalling when cold just above idle. It started fine and once warm it ran better, but not great. Even when warmed up the engine was weak coming off of idle.
Attempted Fixes: Disconnected, inspected, reconnected both ECM connectors. No change...still got MIL's & engine ran rough just above idle.
Needed to do 24K valve inspection, so while checking the valves, tried a few more fixes. Disconnected, inspected, blew out with compressed air, & reconnected connectors associated with checking valves (MAP, Throttle Position (TP), both Fuel Injectors, Inlet Air Temp (IAT), Idle Air Control Valve (IACV), Cam Position (CMP?), Pulse Air something something (PAIR?), fuel pump, 10 wire multipin connector (it contain MAP, Fuel injectors, TP, IACV, CMP signals). I didn't find any smoking gun on the connectors, but a few of them felt weakly connected. I also relieved the stress on the IAT sensor (at the front of the air cleaner) wiring going into the wire harness by cutting back some electrical tape. Found some fouling on the rear spark plug, and replaced both spark plugs. Found some excess dirt and grim around the insulator under the rear throttle body possibly indicating some air leakage into the rear cylinder. This could explain poor engine performance just above throttle and fouled spark plug. Inspected wiring harnesses, fuel lines, vacuum lines....no problems found.
End result: Put everything together and have been trouble-free for ~500 miles, ~30 starts, >100 cycling of ignition switch. Engine runs strong at low rpms again, and no MIL's!! Total cost- $0. Special tools needed--service manual. I suspect a connector was loose/corroded/dirty & possibly throttle body was also jarred loose when NT was dropped.
The service manual is very good at giving information on how to fix MIL's & stresses to check all connectors before checking sensors and the ECM, but it doesn't ever mention the 10 multipin connector containing the MAP signal.
As much pain as checking the valves every 8K miles is, it does provides the opportunity to look at the air-in and air-fuel-out sides of the throttle bodies, inspect vacuum hoses & fuel lines & wire harnesses, pull spark plugs..etc. And my valves didn't need adjustment at 24K after making the first adjustment on the front exhaust valves at 16K.
I bought a MAP Sensor thinking that if MIL's continue after the above inspections, that then it would be a good time to replace the MAP Sensor. So far, so good. The Honda dealer has a 30-day-return-for-full-refund policy if the part is not used. I haven't opened the new MAP sensor package.
It is somewhat unsatisfying to not find a failed component, but that is the way it can be with intermittent electrical faults.
Symptoms: A solid MIL lit when ignition key turned to start. Most times it would clear by cycling the ignition switch, on a few occasions the MIL stayed solid. Could also clear MIL by cycling engine kill switch. Active MIL's were always an ECM code 1- Manifold Absolute Pressure (MAP). Stored codes in the ECM were always (and only) a 1, MAP voltage, hi or lo.
A few weeks ago the NT started stalling when cold just above idle. It started fine and once warm it ran better, but not great. Even when warmed up the engine was weak coming off of idle.
Attempted Fixes: Disconnected, inspected, reconnected both ECM connectors. No change...still got MIL's & engine ran rough just above idle.
Needed to do 24K valve inspection, so while checking the valves, tried a few more fixes. Disconnected, inspected, blew out with compressed air, & reconnected connectors associated with checking valves (MAP, Throttle Position (TP), both Fuel Injectors, Inlet Air Temp (IAT), Idle Air Control Valve (IACV), Cam Position (CMP?), Pulse Air something something (PAIR?), fuel pump, 10 wire multipin connector (it contain MAP, Fuel injectors, TP, IACV, CMP signals). I didn't find any smoking gun on the connectors, but a few of them felt weakly connected. I also relieved the stress on the IAT sensor (at the front of the air cleaner) wiring going into the wire harness by cutting back some electrical tape. Found some fouling on the rear spark plug, and replaced both spark plugs. Found some excess dirt and grim around the insulator under the rear throttle body possibly indicating some air leakage into the rear cylinder. This could explain poor engine performance just above throttle and fouled spark plug. Inspected wiring harnesses, fuel lines, vacuum lines....no problems found.
End result: Put everything together and have been trouble-free for ~500 miles, ~30 starts, >100 cycling of ignition switch. Engine runs strong at low rpms again, and no MIL's!! Total cost- $0. Special tools needed--service manual. I suspect a connector was loose/corroded/dirty & possibly throttle body was also jarred loose when NT was dropped.
The service manual is very good at giving information on how to fix MIL's & stresses to check all connectors before checking sensors and the ECM, but it doesn't ever mention the 10 multipin connector containing the MAP signal.
As much pain as checking the valves every 8K miles is, it does provides the opportunity to look at the air-in and air-fuel-out sides of the throttle bodies, inspect vacuum hoses & fuel lines & wire harnesses, pull spark plugs..etc. And my valves didn't need adjustment at 24K after making the first adjustment on the front exhaust valves at 16K.
I bought a MAP Sensor thinking that if MIL's continue after the above inspections, that then it would be a good time to replace the MAP Sensor. So far, so good. The Honda dealer has a 30-day-return-for-full-refund policy if the part is not used. I haven't opened the new MAP sensor package.
It is somewhat unsatisfying to not find a failed component, but that is the way it can be with intermittent electrical faults.
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