Ok I have about 3 problems that are all probably related. I have a 1990 240 that when I start it up in the A.M. it cranks right up and idles perfect, but when I go to take off the engine falls flat on its face. Once I have driven the car until it warms up it drives fine. Then once the car is at operating temp the idle sits at about 700 rpm but its pretty choppy. And when I am accelerating I have a surge under light load and it goes away under heavy loads. Over the past few thousand miles I have replaced the following parts for various reasons. TPS, Temp sensor, o2 sensor, plugs, wires, cap, rotor,fuel filter, and removed AIV. All of these things have improved the performance, especially removing the AIV, but it still isnt just right. The choppy idle is a newer problem and doesnt seem to correspond with any work that I have performed. Anyways, any advice would be greatly appreciated.
Thanks,Phil
Choppy Idle and acceleration surge
one thing that helped my acceleration hesitation was redoing all the engine grounds and cleaning the contact surfaces.
theres an engine to chassis ground top right rear of the engine (when facing car from front) very flimsy wierd contruction, somewhat corroded as well.
engine to chassis to battery ground off of the intake manifold (left side), if you take out the battery and follow the wire it grounds to the battery tray as well, mine was OK but had a fair amount of corrosion.
also you may want to look into running a new ground for your MAS, sometimes redoing the ground will make a nice smooth correct signal for Mr ECU, because the ground wire tends to get alittle flakey around where it connects to the MAS unit.
theres an engine to chassis ground top right rear of the engine (when facing car from front) very flimsy wierd contruction, somewhat corroded as well.
engine to chassis to battery ground off of the intake manifold (left side), if you take out the battery and follow the wire it grounds to the battery tray as well, mine was OK but had a fair amount of corrosion.
also you may want to look into running a new ground for your MAS, sometimes redoing the ground will make a nice smooth correct signal for Mr ECU, because the ground wire tends to get alittle flakey around where it connects to the MAS unit.
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quiksilvia
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FriendshipRacing
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Ok, here's an update. Last night I pulled the car in and removed the idle control assembly from the intake and cleaned it. I also plugged the vaccum line going to the EGR valve for testing purposes. The idle is much better but the surge is still there and the car still falls on its face after a cold start. One more thing I'd like to add is that a while back I went next door and asked a Nissan guy about a stumble I had when shifting (which I later found out was due to the AIV) and he told me it was the o2 sensor and to simply unplug it to see. So I did and it still had the stumble, BUT the surge and the cold start problem went away. So I went next door to Nissan and got a new 02 sensor. As soon as I plugged in th new one the surge and cold start problems came back. That really confuses me, but maybe it'll make sense to one of youguys.
the o2 does not have an effect untill the car goes system goes into closed loop this happens at 158 degrees some models were 172 degrees. so when the car is cold this should not have an effect. unless your cts is faulty or corrosion is present in the harness essientially lieing to the ecm. by creating a open circuit you put the car in a fail safe mode. this may be why your problem goes away when disconnecting the o2. I see in your initial post says you replaced the temp sensor. which one the single wire or the dual wire sensor?
You just said what I have been thinking all along, and what I asked the guy next door. I replaced the 2 wire temp sensor for the ECM for that reason. In fact all of the parts I have replaced are genuine Nissan parts. I work right next door to a Nissan dealership so I just get my parts there since they give me a discount. Anyways, the tech next door had no answer to my question as to why the o2 sensor affected cold performance. I don't have a clue as to how Nissan engine controls work, but GM cars dont use the o2 sensor until they reach operating temp and I figured Nissans were the same since o2 sensors cannot give an accurate reading until they are warm. And I did look at the connector for the temp sensor and the terminals looked great. So if there is a problem it is between there and the ECM, which I have no clue where it is.
