1999 C70 T5 misfires for a minute on cold start, but is ok when warmed up. Is this a common temp sensor problems or a air/fuel mix? Possibly MAF meter?

instead of jumping and guessing the code , have the faults read with a scanner
what you say indicates a problem with the air intake system which includes , Ambient temp sensor
BARS sensor
MAF/VAF sensors
oxygen sensors are after the cat converter and seldom cause an issue but the heated oxygen sensor(HO2S) which is in the exhaust manifold before the cat converter can cause the problem
That sensor reads the exhaust gas composition and reports to the ECM so that the air/ fuel mix can be adjusted for all conditions
If that is not reporting correctly then what you have is an indication of a possible sensor fault

Try the tps, throttle position sensor, and the idacv, idle air control valve. Even sometimes the temp sensor could be bad, telling the motor its cold when its really hot..

I would replace the oxygen sensor (or sensors).

- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

Okay. If the problem occurs when the engine is cold, check for leaking fuel injectors by doing a fuel system pressure bleed down test. A leaking injector will drip a lot of extra fuel into cylinder and cause it to rich misfire until enough air can mix in to lean it out. (Which you are supplying with wide open throttle). If the problem occurs mainly with the engine warm, check the engine coolant temp sensor and the intake air temp sensor. If either of these sensors is stuck at full cold, the computer will send too much fuel to the injectors for a warm start and again flood the engine.

Check the Idle Air Control and crank sensor. See if either one is going bad. Try cleaning the MAF with MAF cleaner or replace it if it's bad. It's usually a process of elimination with cleaning the IAC, MAF or even seafoaming the intake. I do these things first because its cheap. Crank sensors can be effected by temperature and the MAF and IAC will too so too. See what cleaning them will do first.

Hello,
This is my best guess without knowing the yeay and model, but these issues are very common among many vehicles.

There are many things that can trigger your engine light, here are the 3 most common in the order of likelyhood that I would have checked as soon as you can.

1. Dirty air filter. ( this often causes a bad fuel/air mix ratio. The air filter is the engine's lungs.)

2.( MAF), "mass air flow " sensor. ( A faulty MAF can cause rough idle,stalling, and even prevent the engine from starting, particularly in cold weather. This can also cause a very poor fuel/air mix ratio.)

3. Oxygen sensor. ( This also effects the fuel/air mix ratio ),

I hope this helps you.

it may be idle control sensor or a bad mas air flow sensor--maf sensor in otherwords. or could be engine misfire at cold temp. start. only time when cold? or does run better when warm? try warming engine to operating temperature before driving,if problem removes it's self after warm up,up grade gas to 93 octane for 1 tank full. then see if problem goes away. it's cold where you are right? if so the fuel needs to be at least midgrade 89 octane fuel because 87 octane fuel will not start your honda correctly at cold temps. in cold weather 93 or super gas octane will start ,no problem,low octane fuel sometimes gels, or freezes at low temps. if in warm climate, change the fuel filter, add fuel injector cleaner to your fuel tank[preferablly lucas fuel treatment] this will lube your fuel injectors and give better fuel mileage. thank you for choosing fixya.com

po171 is lean on bank 1--===causes --MAF/VAF sensors --injectors ---HO2S (heated oxygen sensor)
po300 is random misfires and po301, 2, 3 4 5 6 etc is the cylinder that is misfiring
most likely that the fuel pressure is below the required pressure either from the pump or blocked filter or the tank not venting properly--- (EVAP) problem
check the fuel pressure ( minimum of 45-65psi) --problem pressure regulator , pump or filter
replace the heated oxygen sensor on bank 1 ( in the exhaust manifold before the cat converter) as it reports to the ECM to get the correct air/fuel mix