For about 4 months my 98 Maxima AT has had a rough idle. The RPMs drop down to about 500 then ping back up to 700. This only happens when the engine is completely warmed up and the brakes are applied. If I switch into Neutral or Park the RPMs jump up to a steady 800.
A few weeks ago I was stuck in bumper to bumper traffic. Without applying the brakes nor gas I was slowly cruising along at about 8mph. While cruising along the engine ran smooth with no pinging. I first thought the brake booster must be affecting the air intake. I tested the booster check valve and found it was allowing vacuum both ways. After replacing that valve the RPMs increased slightly but the pinging still occurrs while idling.

I've cleaned, tested, and replaced a numerous amount of other parts:

1. Disassembled and cleaned the TB, IACV, and EGR giude tube.
2. Inserted NGK platnium plugs.
3. Cleaned and tested the MAF, ECTS, and camshaft pos sensor.
4. Tested the fuel injectors. They all measured at 10.4 ohms.
5. Cleaned the springs within the coils and where they mount on the power transistors. Disconnecting the coils or injectors while the engine is running makes the pinging worse.
6. Cleaned the engine grounds and inserted 4 new ones with 4 AWG wire.
7. Tested for vacuum leaks with a smoke machine.
8. Replaced the front oxygen sensor.
9 Replaced the TPS. I tried repostioning this sensor to adjust the air/ fuel ratio. With a leaner or thicker mixture the pinging got worse so i got it back to 500 ohms with the engine warmed up and the plate closed.
10. Repostioned the throttle plate with the positioning screw. This will evenly effect the air/ fuel ratio.
11. Did the idle relearn procedure.
12. Adjusted the IACV screw.
13. Replaced the fuel and air filters.
14. Replaced the PCV valve.
15. Cleaned and tested the ERG and EGRC solenoids.

Since this doesn't happen in nuetral or when the car is slowly moving with no pedals applied then I presume that it's either the torque converter or the CKP sensor.

I'm going to test both CKP sensors tomorrow. How can I test the torque converter to see if it's operating correctly?

 

Seems that you've not tested the most common cause of loaded idle misfires, the ignition coils.

The torque converter is an extremely unlikely culprit.

 

Between pins 1 & 2 of all the ignition coils I got around 1.4k ohms. On page EC-335 of the FSM it says anything other than 0 ohms is passable? I also tested the ignition coil harness connectors. I got 12V and ground continuity on all connectors. With the engine running I disconnected the ignition coils seperately and the engine knocked around bad each time.

I got no pinging when I was cruising along without the brake or gas pedals applied. I heard this is called Running Idle. If the coils were bad wouldn't they also cause pinging while at Running Idle?

The only time I got misfire codes is when I disconnected the coils or injectors. I also got codes when I adjusted the TPS or throttle plate positions. With the TPS back to the orginal 500 ohm closed-plate reading no codes will appear but I'll still get pinging while idling. The engine only pings when I'm idling with the brakes applied. I heard this is called Minimum Idle.

 

On page EC-335 of the FSM it states that anything other than 0 ohms between pins 1 & 2 of the igntion coils is passable:

__|__
(3|2|1)


In the chilton manual is states you should read 0.8 ohms between pins 1 & 2:

__|__
(1|2|3)

The ignition coil pins are labelled backwards between the FSM and Chiltons manual.

Please tell me how I should label the pins and what resistance reading I should get?

 

I'd like to know what procedure you used to set the default throttle stop? There is a correct way to set that up along with the IACV. Also there is no Idle Relearn on a 4th gen. FWIW - A misfire shouldn't be caused by either of the two.
A clogged injector will not show up on an OHM meter. Can you pinpoint which cylinder is causing the misfire or is it a multi cylinder misfire?

 

Before I touched the IACV screw, the throtle plate screw or the TPS I got no misfire readings. I only got pinging while idling. With the idle RPM reading so low I fisrt tried adjusting the IACV screw to allow more air intake. The idle RPM would increase but the pinging would still occur. I then tried adjusting the throtlle screw to allow more air/ fuel intake. Before I touched the throttle screw for the first time I marked where the nut is located on the bolt. The RPM would increase but the pinging would still ocurr. I then tried repositioning the new TPS. With the plate fully closed I got 500 ohms. I positioned the TPS to 600 ohms. With this thicker air/ fuel mixture I heard the step motor within the IACV squeaking for the first time. This would cause pinging while in neutral and gave me a P0301 code. I swapped coils 1 & 3 but I still got P0301. I then positioned the TPS to get 400 ohms with the plate fully closed. With this leaner air/ fuel mixture the IACV step motor would no longer squeak but I still got a P0301 code. I presume this is caused by the ECM injecting more fuel to adjust the air/ fuel ratio. The only time I got a P0300 code is when I disconnected the coils with the engine running.
With the TPS and throttle plate screw back to its orignal settings I no longer get any misfire codes but the engine still pings while idling.
To set the idle I disconnect the TPS connector with the car running in neutral and I adjust the IACV screw to get around 750 RPM.
For the first 12 years I've mostly used 89 octane fuel but I'd pour chevron fuel injector cleaner or sea foam in my tank once every 3 to 4 months. For the past 3 months I've used only 93 octane fuel but the pinging still occurs. Since swapping coils made no difference in the P0301 code could it be that fuel injector 1 is clogged?

 

Air/Fuel is controlled by the o2 sensors. Your theory on adjusting the a/f by adjusting the throttle stop or IACV is incorrect.

I think you need to define what you call PINGING?

 

To set the default throttle stop:

Engine completely up to operating temp, no accessories on, no CEL.
Turn off engine and disconnect the TPS.
(this will make the IACV inactive for the next step)
Restart the engine and set the idle speed to ~550 RPM's - This should NOT set a CEL.
Turn off engine and reconnect TPS.

I think at this point you should set the TPS correctly by following this procedure.
http://www.lyberty.com/car/Maxima_A3...NTB99-053b.pdf

Once that is done if your idle speed is incorrect, adjust it by means of the IACV.

I'm curious to what you define "pinging" as?

Engine knock and ping usually presents itself under a load, not at idle.

 

The air/ fuel ratio is measured by the O2 sensors. When the throttle plate is opened further with the adjustment screw the TPS and MAF sensors will both give a higher voltage reading. This will increase the idle RPM but the O2 sensor voltage readings remained the same. I verified this with the Nissan Datascan SW I used with my nissan consult interface.
When my friend opened the IACV screw further the RPM and MAF sensor voltages increased. The O2 sensors voltage increased for a miilisecond but then adjusted back to the original reading. Next time I use Datascan I'll check to see if the fuel injectors give a different timing while adjusting the IACV screw.
When I repositioned the TPS I didn't use datascan but only measured it's resistance.
With the engine rpms jumping while idling I used datascan. The MAF voltage and fuel injector timing would increase during a ping. The TPS voltage remained the same. Next time I test this I'll have to check the O2 voltage readings.
The pinging only ocurrs when I'm idling with the brakes applied and the engine is fully warmed up. The RPM drops to around 500 then jumps back a few hundred RPMs. This rpm rattling doesn't ocurr when idle running, but only when the brakes are applied.
Other 4th generation owners have had this problem. I've spent hours reading other posts regarding this matter. I started my own thread because I didn't want to open an old one:

http://forums.maxima.org/4th-generat...when-stop.html

It seems as though no one has found the answer as to why the RPMs rattle when idling at a stop.

 

When I disconnected the TPS I never restarted the engine so I might of screwed up there. Thanks for TPS adjustment procudure. I printed it and will try it in a few hours.

I recorrect what I stated earlier. I just read that forum again and he found the solution:

Hey!!!! The Other Day I Put In Nos Octane Booster (racing Formula For Offroad Use) And The Shaking Stopped After I Used Half A Tank Of Gas. I Guess One Of My Injectors Was Really Dirty Or Clogged. I Am Sooooo Happy.


I've used Chevron and Sea Foam plenty of times but I haven't tried Nos octane booster yet. I used 89 octane fuel the first 12 years so the fuel injectors are proabaly clogged. When I swapped coils 1 & 3 I still got P0301 so a clogged injectors could be the culprit.

The throttle plate screw and TPS position are back to their original settings so I'll try that TPS adjustment procedure along with the NOS octane booster.

 

Carbon build up in the combustion chambers was causing detonation.

A few other forums stated that using octane booster would stop the RPM rattling while idling. Our engines require high octane gas because of the high compression ratio. If the idle rpm rattles when using premium gas, then it's probably carbon build up somewhere if you're getting no codes. I already cleaned every air-intake chamber. I tested and cleaned the coils. I tested the injectors and cleaned them by adding techron and seafoam several times over the last 6 months.
I cleaned the air intake and combustion chambers a few months ago using seafoam as the cleaning agent. That made no difference because I flooded the engine with both air and seafoam with the engine idling. I did it last weekend at a much slower pace:

1. Get the engine fully warmed up.
2. With the engine shut off disconnect the brake booster hose. (This has to be done after the booster check valve. Any fluid will ruin the check valve.)
3. Insert a 2 foot hose with a smaller diameter into the brake booster hose. Temporarily block this hose with something.
4. Start the engine then open the throttle plate to get the engine running to at least 2000 rpm.
5. Open the connected hose and dip it into the seafoam for about 1 second. After withdrawing the hose wait about 5 seconds then dip it again. Keep the engine running at 2000 rpm while doing this.
6. After using up about 3/4 of the seafoam flood the engine with the rest of the bottle while slowly releasing the plate.
7. After letting it sit overnight take her for at least a 20 minute ride. If the chambers were heavily clogged with carbon it may take a few pedal pumps to get it started.
8. Doe the air intake cleaning again but this time use water instead of the cleaning agent. I refilled the seafoam can with distilled water.
9. Now take her for an Italian Tune-Up.

My brother is a trooper and got me a clear spot on the interstate. With the OverDrive off I drove at 90 to 100mph for at least 20 minutes. The engine went from 4500 to 5500 rpm.

It now idles smoothly at 600 rpm. I don't even need to apply the brakes when waiting at a light. Using 89 octane gas is what got these combustion chambers clogged with carbon. To keep them cleaner I'll use nothing but premium from now on.

 

Is your transmission slipping?

Btw, I did the revised TPS adjustment. Doing the thinner (.012 in)/thicker (.016 in) feeler gauge test on the warmed up throttle stop measurement, I had continuity on both, so I adjusted the TPS so the thicker didnt have continuity, and left the thinner with continuity, and now the tranny shifts smoother and more consistent.

 

The rpm wasn't jumping but varied along with the speed. I guess I worded that wrong
While adjusting that stopper screw it did temporarily roughen up the gear changes along with some misfire readings. I also have a feeler gauge so I should measure it while it's warmed up. It's running smooth now but it couldn't hurt to check it.

 

12 or 13 years of carbon buildup will definitely effect idle. I use fuel injector cleaner every 2 wks. Im jus **** like that.

What brand octane booster?

 

Nos octane booster immediately took away the rpm rattling. Getting that power on one gas tank only gave temporary relief. Doing the octane boost, the techron and seafoam injector cleanings, and the seafoam carbon combustion chamber cleaning fixed the rpm rattling.