The gaskets that could leak would be throttle body to plenum, upper plenum to lower plenum, lower plenum to intake manifold, manifold to heads. It's not possible to get spray cleaner down into some of those gasket areas. That's why I usually just do the pedal stomp method if it bogs or there's a hesitation it's usually because air fuel ratio is off and thus a vacuum leak. You could also try cleaning the MAF.

 

Honestly you don't even need to be driving the car to do this when it's parked just stomp the pedal to the floor and see if the engine RPMs fly immediately or if it kind of bogs for a second and then takes off.

 

Mines is worse.. I still have yet to figure out the issue only difference is I have extended crank times slow to start and rpms drop crazy low when fully warmed up. It did have cel lights but those are long gone and fixed. I recently purchased the vehicle and it wasn't doing this before it was after I cleaned the throttle body I made sure to life the plate too and clean everything.


https://m.youtube.com/watch?v=vs_u3O...ature=youtu.be

 

Did you do the idle air recalibration after you cleaned the TB? If not that's probably the issue.

 

I did this test recently along with going WOT and I did not have any hesitation, the RPMs went quickly. I am continued to be stumped by this issue. I have a bluetooth OBD scanner coming Saturday to check again for hidden/pending codes but I don't have anything on the dash.

If it isn't a vacuum leak, could it be something fuel related? It only happens when I take my foot off the gas, I can accelerate fine and from a straight line it is normal. This may be a stretch but back in October or November I had a rough starting issue. I replaced the battery but I didn't fix it until I ran Techron Fuel System Cleaner through the tank. The problem went away after that and the rpm drop was noticed roughly around the same time.

I know it's a stretch and could certainly be a coincidence, I tried running another bottle through a few weeks ago but it didn't help the rpm drop after letting off the throttle. I'd expect a CEL or larger issue with a fuel problem, do you have any other ideas? I'm expecting to find no codes when I scan on Saturday, but maybe I can try to check some sensors or other readings too. Let me know what you think, thanks again for all the help here. Weird one for sure.

 

Might be a lazy O2 sensor, a realtime scanner will confirm this. I prefer the BAFX OBD2 adapter and the Android app Torque Pro. You can select both those sensors and watch them on a graph in real time to see if the rpm bounce happens when the sensor swings wildly one way or the other.

You can also use that combination to troubleshoot possible fuel/vacuum issues by watching your short term fuel trim and long term fuel trim to see if it's having to add/subtract a lot of fuel. CEL won't turn on until it's like +/- 25% fuel I think.

 

The adapter came in today and I just plugged it in and went for a drive. I don't have any codes, it popped up with absolutely nothing. I was trying to watch the 02 sensors and fuel trims but they were constantly moving and I don't know exactly what I'm looking for.

After my drive I was watching the numbers at idle and my rpms would move between 700 to 712 back and forth at idle. It's such a small fluctuation that it doesn't move the needle enough to notice, not sure if that is normal. At idle after the drive my long term fuel % trim bank 1 was about 11.72% and long term fuel % trim bank 2 was 4.69%. The short term bank 1 would move around at idle but stay under like 6% and short term bank 2 would be around 4-5ish.

For 02 sensors at idle, they both had voltage but but only oxygen sensor 1 bank 1 and sensor 1 bank 2 would display a reading. Oxygen sensor 2 bank 1 and sensor 2 bank 2 would read NA % for short term fuel trim. I'm not sure if anything is out of the ordinary here, I can monitor when driving more if I know what to look for from this data. All of the tests it ran while driving came back complete and passed, and there were no codes. Thanks for the help Cleric.

 

The only ones you need to watch are the sensor 1 bank 1/2 data. That's your upstream air/fuel sensors that determine your fuel correction. The second set of sensors after the cats sensor2 is just for catalytic efficiency so it knows your cats are still working.

Basically what you want to do in Torque is go into GRAPHING, then "select X axis sensors" and chose the sensor1bank1, sensor1bank2, and engine rpm. Then try to get the rpm's to bounce and watch the O2 sensor data to see if it also has a change. You can log the data so you can just go out and replicate the issue then pull over and scroll back through the graph and find the dip in rpm and zoom in on just that part of the graph to see what the O2 sensors are doing.

You can also go into "test results" then click the 3dot menu at the top right and pick "O2 data" to watch individual O2 sensors at idle to verify they cycle properly. The same 3dot menu will let you select either O2 sensor so you can look at them one at a time. There is also "test status view".

 

Also, when logging data you can save it as a .CSV file (spreadsheet data) then upload it into a spreadsheet plotter like the free web-based one at csvplot.com and then use a computer to look through the data. Usually easier than trying to do it all on your phone but with the inconvenience of needing a PC.

 

So I just went for a drive and collected some data that I included in the CSV file below. I have an iphone so I used the OBD fusion app which is rated highly, I could not find the torque one. I tried watching the rpms with the sensor 1 bank 1/2 02 sensors but the app's sensor readings were not immediate so it was difficult. If this data is not good or useful then I can try to find an app to graph it or see if I can try again with this one.

I assumed you were talking about the O2 voltage for sensor 1 banks 1 and 2 and I noticed that bank 1 would be around 0.3 V and bank 2 was around 0.6 V. In the data there are a few points where bank 1 hit 0.8 and bank 2 hit 1.275 while I was on the highway. I'm not sure if these are for the A/F ratio or not, I'm having a hard time interpreting the data. I can't find anything to point me towards a problem because I'm not familiar with any readings or where they should be.

I included rpms, speed, MAF rate, STFT and LTFT in the CSV file I attached. If it's too messy or does not help please let me know and I will try again with some other sensors or readings. I tried to make the file more clear and neat on my PC to be able to read it better. Thanks so much for the help, I'm not getting any codes but I'm not sure if these readings will tell you anything about a potential vacuum leak or problem. If you have the time to check it out I would really appreciate it, I can definitely try again if this isn't the right data.

 

So I just paid an extra $10 on the obd fusion app to read advanced codes for 2006 Infiniti. The general OBD2 and ECM scans came up empty. However, when scanning the AT I got a pending code P1815 MMODE Switch. When I scanned the ABS I got confirmed C1109 but it didn't come up for the general OBD codes and I do not have any warnings on my dash. Could either of these connect to the rpm jump I am seeing? I'm not familiar with either code or what they mean. As a side note, I have a newer battery that was reading 12.5V on the app. I put screenshots of them below, weird to me that it says confirmed but I have no issues with ABS or CELs.

edit: just unplugged battery and wiped down connectors and got a reading of 13.5 V on average with the car on. Also went for a drive and used MM mode and it worked fine, shifted gears up and down.

edit 2: cleared both codes yesterday and after a drive, neither of them returned. Went for drive this morning, and afterwards the P1815 MMode Switch was pending again on the scanner. I have had some slight issues with manual mode in the past but it works so I think it's just that little switch in the shifter assembly getting stuck when going up/down once in a while. I don't see how that would cause my RPM drop in Drive though, let me know what you think here. Thanks

 

Just looked around the hoses and I'm hearing some hissing from the PCV valve area. Is this supposed to hiss or could this be a vacuum leak? It's not extremely loud but I definitely hear a hissing noise when I'm close to it.

 

They hiss a little just due to the velocity of the air travelling through it, if you suspect a vacuum leak though spray a little throttle body cleaner at all the fittings on the hose and see if your idle drops.

 

Replaced the PCV valve and the hose that connects to it, hissing seems to have gone down a bit. The old PCV barely rattles when I shake it and seems pretty blocked up but the old hose doesn't have any apparent cracks.

Just went for a drive afterwards and I'm still getting the rpm surges when letting off the gas. I did the idle relearn just in case there was a vacuum leak, it's so hard to tell whether it works or not. Too bad I don't have an android for the NDSII app. Even if the relearn didn't take the first time, I'm guessing the rpm problem would've been a little better after the fix. I can try the relearn again tomorrow but since my idle is solid I don't even know if it's a vacuum leak anymore.

 

Got a vacuum gauge and just checked it at idle and it was in the solid green area at like 21 hg. The gauge wasn't moving at all and I used the check valve on front of the plenum. I'm guessing that this would mean I don't have a vacuum leak.

At idle I was getting like 15% ish for my LTFT bank 1, so I'm wondering if I'm running lean and somehow it has something to do with my rpms jumping. Bank 2 for LTFT sit at like 6-7%. It seems like something is causing me to run lean on bank 1 but not enough to throw a CEL. Let me know what you think. Thanks Cleric.