This started out of the blue last week. It randomly shakes and stumbles like the engine is cuting out both during cruising and acceleration. After some of these episodes the idle has dropped very low and nearly died. No gear or amount of load seems to make a difference.

There are no codes or anything to go on really.

Also since this started, the idle is hanging up pretty like 1100 for several seconds before dropping back down to 750 each time going to neutral. I don’t know what that means or if it’s related.


It does randomly few times a day, or not at all for a few days.

A shop looked at it and replaced the IACV but now it is doing this again a few days later. The IACV i know was pretty bad but obviously not related to stumbling at speed.


What could be related is getting rear-ended hard two weeks ago, which i guess could have knocked something loose. If so what would that likely be?


So when I take it back to the shop, I’m wondering what all you would have them look at? They checked the fuel pressure, and all the computer connections and sensors and cleaned the MAF and everything else that I can think of.

 

Since the problem occurred after the accident, there might be a relationship.

This issue might be related to a vaccuum leak from the back of the car. I'm thinking that one or more parts near the charcoal canister might have been damaged or come loose. Take a look back there.

 

That’s a great idea, but I’m not finding any sign of a vacuum leak so far, near the can or anywhere in the front.


I have also checked out the harness connections t0 everything I can find and they seem fine.


Do you think it’s possible the knock sensor could malfunction and make the engine think it’s knocking when it’s not? Then it would severely retard the timing, making it run like crap momentarily?


Besides the obvious stumbling that happens sometimes, there is a subtle, general lack of power and what I would call an inconsistency in throttle response. It’s hard to describe but the car just doesn’t feel right.

 

no j, your thinking of my car.....

 

When my car was doing this, it was the MAF.

 

Do you think the impact could have disturbed the little wires in the MAF, making it act funny?

It was hard enough to push the car five feet forward with the brakes locked. I am amazed the rear end isn’t gone.

I know MAFs can be really tempermental.

The shop said it looked fine when they cleaned it.


I am going to test the TPS also, and if that’s fine, probably replace the MAF.

I feel like the issue is bad input into the ECU, causing it to do strange things, as opposed to an output problem, what the ECU is controlling not working right.

 

Plat, a defective knock sensor does not cause that kind of issue.

An old saying about computers is Garbage in , garbage out.

Inaccurate information in, bad decisions come out.
So it's likely a sensor.

 

MAFs do have internal connections which break. See this thread: https://maxima.org/forums/4th-genera...ml#post7963527. If the connection was already weak, the impact might have been enough to break it loose. And never discount the possibility of coincidence...

 

I had the same problem with the car stumbling and hesitating I changed out the fuel filter and and it fixed the problem

 

The shop ended up deciding that the MAF was bad and replaced it. That seemed to solve the problem for a while, but now it is having issues again.

Starting last week, there is pinging in hot weather. Mostly under high load but sometimes also when driving like granny in 2nd in traffic, mostly around 2k to 2.5k. It seems light and only occasional. Pinging has happened through parts of three tanks of gas from different stations so i doubt that is it. I run 91 only. It also has a bog sometimes the first second when I crack the throttle, and sometimes it pulls first and then bogs, and start pulling again.

There are no codes/SES light.

In the last two years these are new and checked recently by mechanic:

Spark plugs
All Coils
All O2 sensors
Knock sensor
IACV
MAF

The mechanic has previously ruled out the fuel pump and fuel supply issues and said that the fuel trim has been perfect while test driving it.

I don’t know where to go from here. I don’t want to to bring it back to the shop because they have driven it hundreds of miles and claim to have never experienced the hesitation that has.

Could a bad TPS cause issues like mine?

 

The maf sensor has to be OEM Nissan sensor. It cannot be sn aftermarket sensor otherwise you will continue to have problems. The iacv rarely ever go bad on these cars which in your case was not the problem and you spent extra money on something that was not bad. The oem mass air flow sensor always has a pink sticker with the part number 22680-31U05 A36-608 E61. These shops usually have no ideas that they need to use oem parts and instead guess at problems like these.

 

Go to a junkyard and get a couple of used OEM MAF's off a Maxima or I30. They are fairly cheap. Make sure they have the pink sticker on them. Try those. ^^^^ Aftermarket MAF's don't work well on our cars.

 

I'll put in a used OEM to try. The shop put in a 'Spectra' one.

I measured my fuel economy today after a 60 mile round trip to work and got 28 mpg. I had been getting 22, and that was after suddenly dropping from 24 a couple of months before the hesitation issues started.

Now I'm wondering, for driving slow and doing 70% highway, shouldn't I be closer to 28 in the first place? And the manual says that light pinging is normal so what if things are actually closer to what they should be? Minus the hesitation of course.


I would really like to drive the car to work through this week. How likely is it that damage is being done by possibly being lean/(seems to me light) pinging? Would you drive it?

 

Add some TCW-3 outboard oil to your gas. Put in 1 ounce to every 2 gallons. It will lubricate and clean you fuel injectors and act as an octane booster. Our cars love this stuff. I have been running it in my I30 for 6 years and many members on this site use it. It will not harm your engine. Also, run premium gas in your tank. I have taken 3 trips from LA to Sacramento lately, to look in on my ageing mother. Its a 500 mile trip, one way. I average 30 mpg on those trips.

 

I have run tcw-3 for a while actually, but that’s way more than i was told
to use, 1 oz per 5 gallons.

I have tried just unpluging the MaF and this makes the car basically undrivable. It stalls and bucks when you try to accelerate and still has pinging. I thought that if the MAF was a problem then running without it could make an improvement?

I got a live scan tool and see the advance going from 15* at idle all the way up to 44* in some cases.
it is pinging the advance is from 35-40*. Does this amount of advance sound right?

Everything else the scan tool shows looks good, O2s are responsive.I will scan the STFT and LTFT on the way to work and report back.

Now that i have a scan tool, is there anything else I can check to narrow this down?

 

Just posted this for another user, but a bad crankshaft position sensor caused this problem for me. I replaced the fuel filter and the MAF and neither thing solved it. No codes, no nothing. Got it towed to a shop and they figured out it was the crankshaft position sensor.

 

Thank you Shrout, I’ll consider that as a next step. It is a bit pricey so i’d want to rule out more stuff first.

I am getting LTFT at +5 to +8 while cruising, and dropping to negative when i accelerate. Does this sound too lean overall?

I also have seen one time that the MAF reading just stuck and didn’t change when i floored it. This must be where my bog
is coming from.