# hesitation while driving ('90 Maxima SE)



## BuffaloRider (Jul 16, 2014)

Anyone have experience with these symptoms (below) and how you fixed this? 

I have replaced all my vacuum hoses, new EGR Valve, new EGR solenoid, Power Actuator Solenoid checked (and is working), new O2 sensor, new PCV Valve, new spark plugs. 

Car has two intermittent problems - while driving car will at times run rough (as if going back and forth between hesitate & normal), and then return to normal for awhile, then back to the running rough (hesitate-normal cycle). 

Second occurs at idle - runs at 800 rpm, then will speed to 1300 rpm for a couple of seconds, then back to 800 for a few seconds, then back to 1300. Then car will run normal for awhile (steady 800 rpm at idle), then the 800-1300 back and forth thing will happen again. 

I will be putting on a new throttle sensor, and I cleaned the airflow meter with non-chlorinated brake cleaner spray today. 

I have not checked the codes on the computer (ECCS Control Unit) yet. Will check tomorrow.


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## smj999smj (Jan 1, 2006)

Fuel injectors were a fairly common cause of misfires/hesitation "back in the day." There were several different injectors available identified by a colored paint dot on the injector, which identified the spray pattern. Check for vacuum leaks or a dirty or faulty AAC valve.


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## BuffaloRider (Jul 16, 2014)

smj999smj said:


> Fuel injectors were a fairly common cause of misfires/hesitation "back in the day." There were several different injectors available identified by a colored paint dot on the injector, which identified the spray pattern. Check for vacuum leaks or a dirty or faulty AAC valve.


Picked up a spare A.A.C. valve at a salvage yard. This is a part that is no longer sold in the aftermarket, apparently. Per the Nissan Service Manual, it passes the 'resistance test' for a good valve. I assume, but do not yet know for sure, if the stepper motor still works as it should. I took it apart and cleaned it - quite a bit of carbon powder in it - all parts should now move freely. I will be taking the one off my car and clean it in the same way. Hopefully one of the two will still be good. 

I do not think there is a problem with the injectors, at least not at this point in time.


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## BuffaloRider (Jul 16, 2014)

I have done quite a bit of diagnostics on this since my original post. I will provide this update in case it helps others. My car has two issues - it has spurts of hesitation at times while driving, and after the car has warmed up the idle speed is often at 1400 rpm, but should be about 800. 

I suspect these parts may be bad, sticking, or failing intermittently. The hesitation is intermittent, so (as with all intermittent problems) it is difficult to pin down. 
o A.A.C. valve is a suspect (picked up a used one at a salvage yard)
- I have cleaned this one, will also clean the one on my car.
o Mass Air Flow (MAF) sensor may be cutting in and out. 
- could be failing due to connector, which I have cleaned and creamed. 
- also cleaned my sensor, per a mechanics recommendation, with brake cleaner.
- have since found there is MAF cleaner out there, which is better
- I picked up a spare MAF at a salvage yard, do not yet know it if is good.
- This part can still be found new or remanufactured. 
o throttle valves - may be dirty. 
- I will be taking this apart and cleaning them. 
- if carbon around the throttle valves, it can restrict airflow at idle (which is bad)
o Air Cut Valve (works in conjunction with the A.A.C valve).
- I doubt it is bad, but I will clean it. 
- Also picked up a spare at the salvage yard. 

I used the cars onboard computer for diagnosis as well. Mode III gives me a code 21, which the Service Manual says "ignition signal missing in primary coil" - this does not make sense to me since the car runs and is driveable - if there was no signal, there would be no spark - so perhaps there is a harness connector problem. Mode V (real time diagnostic) also shows the "ignition signal missing in primary coil." I monitored Mode V by putting a camcorder on the floor of the passenger side, was able to record the entire time I drove the car (about 25 minutes). Showed ONLY the ignition problem.

Interestingly, in Mode V (and Mode III) I did not get any feedback that the MAF is failing (not even intermittently), nor any other part. I still suspect the MAF since if bad it will prevent rpms over 2000 - and the hesitation puts the engine momentarily into a forced idle. Makes me wonder about how the computer works - if it detects a problem, does it stop there? What if there are multiple problems? With a handheld on an OBD-II car, it will record codes for all the failing parts. I suspect the Maxima's onboard computer does not do this and only shows the first item it detects - so I am wondering if there are failures beyond the ignition-reported issue (which I think is a false positive at this point). 

Once again if anyone has insight in these things let me know.


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## BuffaloRider (Jul 16, 2014)

I may have found the cause of the intermittent hesitation and the high idle. My car has acted odd for a good 18-24 months - so it feels good to have finally narrowed it down and (apparently) fixed it. 

I took off my A.A.C. valve (also called an idle air control valve) and cleaned it good. There was black powder in it (carbon?) that had caked on in places that likely was inhibiting the free movement of the valve when the stepper motor was activated by the cars computer. 

Since I had my mass air flow sensor off the car (had to take off the big plastic intake vent to get at the A.A.C. valve), I also sprayed it good with MAF cleaner that I picked up at Autozone. The MAF cleaner is made for the MAF sensor, so I ditched the brake cleaner I previously used in favor of this stuff. 

Put it back together, drove about 20-30 minutes, various speeds, no more problems. So cross my fingers that it really is fixed, but so far it looks good. I cleaned the MAF a month or so ago, so I don't think cleaning it made much difference - although I cleaned it with the better cleaner this time - MAF cleaner (not brake cleaner). The A.A.C. valve, however, probably made the difference. I wasn't very dirty, but the valve had enough carbon caked on to it that the carbon build-up may have interfered with the valve moving freely in the valve's cylinder. After cleaning, it moved easily. So I think the A.A.C. was the cause (or main cause) of the two problems I have been discussing in this thread - the hesitation problem, and the high idle problem.


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