rough idle and poor acceleration when hot

[jason81]

Hello I have a 94 q45. I have had this car about 6 months now, when i bought it was not running right. I had pulled a code of the computer that "bad injectors" so I had 3 of the injectors replaced. That seem to fix most of all my problems but the car would sometime die as soon as it would start or sometime when i would pull up to a stop light. Anyways about a month ago a new problem started. I would drive the car an it would run perfect, but then after about 15 minutes of driving, when the car would warm up to its normal temp, the car starts shaking. The more i push on the gas the more it shakes. I am not getting a check engine light either. When the car starts doing this it seem like it has no power and dosnt seem to want to shift correctly. I think the problem is getting worse, because now it is acting this was as soon as i start it. Oh yeah, also sometimes when i go to accelerate i hear a misfire/backfire from inside the motor. Please someone out the give me some advice, I want to get my Q back to normal. I have tried running some lucas injector clean through it, some "heat" to rule out water in the gas, replaced the fuel filter, disconnected the battery to reset the computer. I am thinking maybe it could be a coil, knock sensors, vacuum line, or ? I am not getting any kind message or check engine light, can someone please help me out, Thanks

[Infinitiguy19]

Run a vacuum pressure check (AKA Lower than atmospheric pressure test).

Then check the injectors resistance when hot (Fully warmed up 176*F) and cold (60*F or less) Coolant temperature.

Run some Redline S1 with a half a tank of gas or more and change engine oil and filter in a week or less. If that doesn't fix the issue then perform a BG injector flush.

[dana0330]

I had a similar problem with my 92 I has 3 bad injector in it and I replaced all 8 with rebuilt injectors and they all failed. I put in a set from Deatschwerks I also had to get the adapter kit for my Q. The only way I could find out the injectors were bad was when the engine was hot I disconnected the injector harness for the ground wires and I grounded them on at a time and 5 would not click and 3 would checking resistance would not work they all read ok.

[kevindanielk]

Might also be your Mass Air Flow sensor. It doesn't seem to throw a trouble code on the Q. I had the same problems that you describe, when I first got my 95Q, so I physically opened up my MAF and re-soldered all the connections on the circuit board, resealed it back up with silicone and it's worked perfectly ever since. I've also done this same MAF opening up and re-soldering on a horrible running Maxima and it's also been running perfectly ever since. Just my 2 cents.

[Locknut]

If you have scoped (you can use a long screw driver) and ohmed your injectors, and checked your MAF connector (wiggled it, crimped it, put dielectric grease on it)....try checking your EGR value after the engine gets warmed up. Put your fingers underneath the value and see that its flutters at around 2k rpm. Push it up and down to make sure it isn't stuck. Take off the vacuum hose and make sure there is vacuum to it. This is just one of many things (fuel pressure, plugs, coils, etc) that causes stumbles and loss of power. The real experts here will wade in over time, and you'll get er fixed. Good Luck

[Locknut]

another word of advice....do not test or touch the maf circuit board with the top copper plate removed while it's powered and risk shorting it out....seems like a no brainer but well....ya know what I'm saying....

[jason81]

update: so i got another maf and it didnt help anything out. i stuck my finger under the egr valve an revved the engine up, i felt it go up, and then went the rpm's got a higher it went back down, is that how it normally works? i have found another Q at a pull a part so what do you all think i should try next? thanks

[Locknut]

Yeah the egr sounds good....now scope the injectors with a long screw driver. Does the engine fire right up or does it turn over for awhile. Does your fuel pump buzz? Feel your FPCU after the engine has been run awhile...is it hot? Get a fuel pressure gage and put it in between the new fuel filter you are going to put in...and the fuel rail. 34 psi at idle...then pull the vacuum hose on the fuel pressure regulator (drivers side back of fuel rail)....psi should go up to around 40. Then shut her down and watch the fuel pressure bleed down. If it goes below 10psi in less than ten minutes or so...you got a leaky injector....if not then you can check the coils and plugs...7 and 8 are fun to work with. Don't get discouraged, we all feel your pain...Keep us posted.

[Locknut]

Couple of other easy things to do....unplug the AAC solenoid after the car is warmed up..you should get a nice drop in rpm. check the pcv valve...you should have good suction...and check your throttle plate...if it's gummed up...spray it off with some carb cleaner...clean your temp sensor connector too. One last thing....while your doing all this you might want to consider getting yourself a consult cable and Nissan Scantech software for your laptop and do a power balance before you start in on your plugs and coils...or consider taking it to a dealer to have one done. It could save you a ton of time and money in the long run. Good luck.