I replaced my spark plugs yesterday following the DIY.I also cleaned the throttle bodies (following the DIY), and replaced a couple intake hoses. Everything went pretty smoothly and the car is driving great. Its taking a long to start however. It cranks strong but longer than it should. Does anyone have ay suggestions on what that might be about? It didn't behave like this before the plug change so its very likely something I did yesterday. Any thought on where I might start looking?

 

I would remove and check all the coil packs, make sure you didn't bend any pins in the electrical connector, verify spark plug torque, look up inside the coil pack well boot and make sure the spring isn't rusty/crusty.

Verify the intake tract is properly sealed and that something didn't get torn during removal/installation.

I would also perform all the resets outlined in this thread.

https://nicoclub.com/archives/g35-35...procedure.html

 

Thanks for the advice. I'll try the resets and go from there. I figured it wasn't an ECU issue since the idle and throttle response seem normal once the car is running. I used a torque wrench so I'm confident I have all the plugs torqued to 14.5 ft-lb. The coil packs all looked when I had them out although I didn't look in the well boot. I live in Arizona so rust isn't typically an issue. I definitely didn't see any. The only pack I had any issue with was passenger front. I think it's possible that one of the electrical connections got loose while I was struggling there.

I'm curious about your comment with the air intake track. I had to replace both intake hoses to the throttle bodies. The passenger side had a cracked hose going into the small attached box. I assume it's for emissions but I'm not positive what is. On the drivers side the other small attached box had a big hole melted in it. So I replaced both of those but they went in fine. It was a pain making all those hose connections. Is there anything specific I should be looking for other than making sure all the hoses are still in place.

Thanks again!

 

Basically to make sure they mated up properly against the duct and throttle bodies and that the hose clamps are tight and any press-fit hoses like the PCV system are tight and can't be just freely turned.

If you had major vacuum leaks like you described then you DEFINITELY need to perform the idle air reset.

 

It appears that the ECU reset did the trick. I went through the full set of resets but it started easily immediately after the ECU reset procedure. I've started it several times now and took it on a short test drive and everything seems to be in order. Thanks!

I saw the ECU reset procedure in the throttle body cleaning DIY, but I didn't bother since I following the recommended procedure, didn't disconnect any hoses, and never had any rough idle issues. That was my mistake.

192,000 miles and going strong.

 

Awesome, what I suspect was happening was the ECM had substantially modified the Long Term Fuel Trim by adding a LOT of extra fuel to compensate for the large vacuum leaks present, however it wasnt greater than +25% fuel over the base trim so it never threw a check engine light. After you fixed the leaks the LTFT was still greatly increased but during startup was causing an overly rich situation that took a few extra engine revolutions to finally ignite.

This problem would have EVENTUALLY cleared itself as the LTFT returned itself back to a lower level but doing an ECM reset causes the fuel trim margin to return to zero and start fresh (that's all an ECM reset does on vehicles).

Glad it's all working properly now. In the future anytime you replace components on a vehicle it's a good rule of thumb to reset the ECM. In vehicles that don't have a physical idle air control valve but instead rely on a volume algorithm like the G35 you also want to reset the idle air volume.

The rest of the resets aren't really necessary unless you have replaced either the accelerator pedal switch (gas pedal) or unplugged/replaced the throttle body. In both cases the ECM needs to learn where "zero" is on those two items before they work properly.

 

I'm sure your assessment is right on. I decided to change the plugs because I noticed my fuel economy drop about 15% over the past month or so. I found the hose issues in the process and the plugs I took out really didn't look that bad.

 

I'm not doubting you at all, but I was always under the impression that the car starts rich anyway and the L/SFT's don't come into affect until the engine reaches operating temperature? Again, I'm just asking for my own clarification or does it only use the A/F sensor and MAF sensor when it reaches operating temperature?

I would think it would be when he cleaned the throttle body that caused the hard start. Since, the butterfly valve is in a new spot it's getting less air? So, you would still be correct that it had an abundance amount of fuel.

 

Most of the vehicles I've seen throughout that era did apply fuel trim to injector pulse length during starting but I've never actually measured for comparison on the G so it's just a guess. You're correct about the open loop starting mode not calculating those sensors at initial start, it waits until there is a signal sent back from the heated O2 sensors, it's not actually reliant on the coolant temperature you see on the instrument cluster. It takes about 30 seconds in the summer, maybe double that in the winter before it goes into closed loop mode. One sign of a worn O2 sensor is a very long initial heat time.

The butterfly valve (TPS) shouldn't have a different zero stop position though, and he didn't unplug it, but accumulation (or the removal of accumulation) behind the plate does alter the amount of airflow at idle.

 

Not sure it matters, but I was pretty careful not to touch the butterfly valve. It may have been slightly shifted just due to me wiping in there but if it did move it was very little and not noticeable to the eye.

 

it's not the butterfly moving per se. It's where it stops at idle. The carbon buildup is like a barrier and when you clean the gunk off in front and around the valve it will slightly close in a different spot. So, it could be enough to throw off the A/F ratio mixture or it couldn't.