hey Guys, Have always had a problem with my zed when cold. For the first 2-3mins of driving she will be very rough i.e. hestition, surging etc as I accelerate through the gears. There is no problem with the rev's hunting, and will idle fine at 1500rpm or lower until she warms up and stays between 700-800rpm.As soon as the temp guage starts to register and start rising, the hesitation and surging will disappear and she will run perfectly. My theory is that the timing might be off which is causing the hesitation (CAS adjusted or something)... Then when the car warms up abit the o2's start to register and ecu starts to adjust air/fuel ratios to compensate for advanced timing, and thus she runs smooth from then on in. As such i plan to check the timing, but thought I would open the subject up for discussion in case anyone else had some theories??
Mayhaps a proper tune is needed . . . the engine runs much richer when cold and may give the symptoms you describe.
some easy things to check... firstly, check your throttle bodies and give them a thorough clean. Gunked up throttle bodies can give hesitation and rough idle. Are you sure your 02 sensors are working properly? faulty 02's can give false info to your ECU and can also run a bit rough when cold. Try checking them and replace if in doubt. also, there have been people with similar symptoms that have had oil/gunk on their AFM which gives false A/F info and runs rough. check your AFM and clean if needed.
AFM was one of my first thoughts, but this was cleaned/inspected when I added my pod filter. Throttle bodies were also cleaned out at this time Datascan shows the 02's are working fine - however I thought the o2's only came into play after the exhaust has warmed them up?
o2s not used during idle the 300zx idles rich, the o2s are only active and used when engine is above idle revs. like 1500rpm. In the first 3 minutes your car is trying to warm up, the revs should be up around 1000 rpm and slowly falling during that time. If the idle is rough the ecu will sense that then increase the idle to smooth it. If everything is working well it should idle between 650 and 750 rpm once warm.
I have the exact same problem. Also I notice that when i touch the accelerator pedal the car feels like its under load and the idle drops. It only does this while its cold. As soon as the temp gauge starts working it always goes straight away.
I also have the exact same problem! Even when its warm, i'm concerned it doesn't have the torque I would expect it to have low in the range... but the hesitation problem while cold is definitely an issue. I haven't run a diagnostic test yet and there are plenty of things to check first, but I thought i'd put the word out there all the same in case someone knows a definite answer. Thanks..
Hey guys, I've done a little research about the problem... I hooked up Ecutalk on my lappy to my 300 this morning. I noticed that when at a cold start, the ignition timing is about 35 degrees BTDC (normal level i assume as the engine is cold). But as soon as I press the accelerator pedal - the timing goes straight down to 15 degrees. If I push the pedal in more then it will go up a little to around 17 or 22 but thats about it. When I take my foot off it goes back to 35. Now as we know: as the engine warms up the timing is decreased in small incriments until it gets back to the base 15 degrees. Once the timing gets under 20 degrees the wierd hesitation and stuff is pretty much gone. I also tried something else! I disconnected the CTS (coolant temp sensor) and when I did this the timing goes straight back to 15 degrees (as it assumes the engine is warm). If I push the pedal in I get no hesitation what so ever. So to me it must be some sensor / electrical problem causing this. Anyone got any ideas? By the way my TPS is set to the correct level (it was originally 0.5 but i changed it back to 0.45 which made no difference anyway).
It sounds like it's over-fueling or not combusting properly when cold. I'm assuming you've checked your error codes? Dirty plugs/wrong temp can cause cold start issues. So can vac leaks, dirty injector connections and stuck aac the list is quite long. Start with plugs and injector connectors.
I also suffer these cold start symptoms. I have a faulty fuel temp sensor to be replaced soon, no other codes present.
