I'm having a bit of a problem narrowing down an issue with my car that started a couple months ago. It’s a 97 NSX-T with a stock engine with an AP-X exhaust. There is no check engine light and no codes in the system. The symptoms that I have are a more than normal lumpy idle, intermittent surging at low speed and low RPM and the intermittent faint smell of gas from the exhaust.
I recently rebuilt the alternator as I found it was shorting out and causing the car to shut off. Main relay is new as well. I replaced all 6 coil packs this year. Timing belt and valve adjustment were done 4 years ago and the fuel filter and spark plugs were replaced at that time.
Troubleshooting steps thus far:
- checked the fuel pressure and it seems to be within spec per the manual
- shorted out the fuel pump resistor and that didn’t change anything
- unplugged the coil packs one at a time to see if the idle changed (or didn’t) – no effect
- checked the coolant level and it’s good
- monitored the coolant temperature via OBD2 port and it doesn’t seem to fluctuate wildly
Checking the threads it seemed that a dirty throttle body could cause this issue. Before I cleaned the throttle body I wanted to measure the base idle (short the service terminal). I shorted out the service terminal per the manual and found that the idle fluctuates (I didn’t detect this when no it service mode). It doesn’t' remain smooth with the service terminal shorted. It starts to run normally then it drops to around 500 and seems like it is going to stall then it recovers. The cycle seems to be to fairly consistent in timing. Based on some other threads I have read it should be running at 600 steady if all is operating normally. It looks very similar to how the system reacts when you turn the A/C on.
I cleaned all the throttle body passages and it did not help the problem (base idle was still fluctuating).
I was thinking O2 sensors, but I thought shorting the service check connector would remove them from the equation. I also thought about an exhaust leak, but I didn’t find any immediate indications of any.
Am I missing anything obvious that I should be checking?
I recently rebuilt the alternator as I found it was shorting out and causing the car to shut off. Main relay is new as well. I replaced all 6 coil packs this year. Timing belt and valve adjustment were done 4 years ago and the fuel filter and spark plugs were replaced at that time.
Troubleshooting steps thus far:
- checked the fuel pressure and it seems to be within spec per the manual
- shorted out the fuel pump resistor and that didn’t change anything
- unplugged the coil packs one at a time to see if the idle changed (or didn’t) – no effect
- checked the coolant level and it’s good
- monitored the coolant temperature via OBD2 port and it doesn’t seem to fluctuate wildly
Checking the threads it seemed that a dirty throttle body could cause this issue. Before I cleaned the throttle body I wanted to measure the base idle (short the service terminal). I shorted out the service terminal per the manual and found that the idle fluctuates (I didn’t detect this when no it service mode). It doesn’t' remain smooth with the service terminal shorted. It starts to run normally then it drops to around 500 and seems like it is going to stall then it recovers. The cycle seems to be to fairly consistent in timing. Based on some other threads I have read it should be running at 600 steady if all is operating normally. It looks very similar to how the system reacts when you turn the A/C on.
I cleaned all the throttle body passages and it did not help the problem (base idle was still fluctuating).
I was thinking O2 sensors, but I thought shorting the service check connector would remove them from the equation. I also thought about an exhaust leak, but I didn’t find any immediate indications of any.
Am I missing anything obvious that I should be checking?