2001 Pathfinder - Engine won't idle; stutters at 1750 RPM when running

[228920Pathfinder]

My pathfinder had one of the common problems back in Feb 2015. The IACV shorted and in the process blew the ECU. This was to be the start of my troubles.

I did a lot of research on this site and was able to diagnose the problem from the engine code and the obvious magic smoke smell from the burned ECU. I set out to fix it all myself since it seemed doable at the time. I obtained a new IACV (Hitachi) and sent my ECU off to a rebuilder (after opening the case to confirm the blown chip). Once I got the new IACV and the rechipped ECU in hand I installed them expecting the vehicle to start and run normally. This didn't happen.

For some reason the vehicle wouldn't idle and I needed to get it back on the road quickly so I had it towed to a dealership in the town where it toasted its chip. They had the vehicle for 6 weeks and never got it running and idling. During this time I ordered another ECU from another rebuilder and had them (dealership) replace the OE ECU with the other rebuilt one to see if that would fix the issue. The replacement ECU came from an Infiniti and had the correct code for the vehicle. Anyway. That didn't work and they were not doing anything useful with it so I picked it up and took it home. At this time it would start and run but wouldn't idle so I had to drive all the way home (100+ miles) keeping a foot on the gas at all the intersections. Fun stuff.

When I got it home I checked the components and tried to use the Idle Relearn procedure documented here to restore all that functionality. I couldn't get the idle to relearn. The vehicle would run but not idle.

Since I also had a transmission code (Transmission Clutch Converter Solenoid related) and the transmission work was still under warranty at a local dealership I took it in to them to have them check the solenoid pack that they had replaced several months prior and also have them perform the idle relearn. Easy peasy. Well not quite.

They were also not able to make the vehicle idle with either ECU and in the process they replaced the MAF sensor and the Throttle Position Sensor. This all done over a period of about 8-12 weeks. They had it a long time and never got it figured out. They also didn't fix the transmission solenoid. When I finally decided they weren't going to fix the problem I drove it home, again doing the foot on the gas part all the way home (25+ miles).

I have multiple vehicles so this one became a lower priority project car while we shifted miles it would normally get to others after the Pathfinder went down.

I just got back into it after not looking at it for several months and this is where I am today: The vehicle will start and run as long as you keep a foot on the accelerator. It dies as soon as you let off the gas. It will hold any RPM steadily as long as you keep your pressure steady except that it stutters at 1750 RPM.

If I try to hold it at 1750 RPM the engine stutters to about 1550 RPM (just reading the tach on the dash for these numbers). It will flutter back and forth between 1750 and 1550 as long as you can hold your foot steady. All others RPMs run smoothly and hold a constant RPM. I have tried this from 4000 RPM down to 1000 RPM. This seems to be the only RPM where I get a stutter.

I used a multimeter to test the IACV off of the vehicle and found resistances varied from 22-23 ohm at about 85 degrees outside temp. I also tested the function of the Throttle Position Sensor with the multimeter and found continuity with throttle closed and loss of continuity with it open and the resistance across the pins was 489 ohms at throttle closed position and 4000 ohms with throttle fully open. These closely match the values given in the manual for these parts so I feel that they are (capable of) functioning correctly.

In the process of trying to bring this thing back to life I also replaced the PCV valve (who thought it was a good idea to put that thing where Nissan put it?) The original PCV valve was nearly completely gummed up. I also replaced all the small diameter vacuum lines and used starter fluid to confirm that there are no vacuum leaks after the lines were replaced (none before either) and the intake manifold gaskets were replaced. I replaced the fuel pressure regulator too.

The vehicle has new - fuel pressure regulator, vacuum lines, intake manifold gasket, throttle body gaskets, IACV, Throttle Position Sensor, MAF sensor, air filter, oil and oil filter, transmission fluid and transmission fluid gasket. It also has a new transmission valve body with new clutch converter solenoid pack. It has a rebuilt ECU with the work being done by a shop in North Texas. I can find the name of it if I need to. They guarantee their work and I have talked to the man who did the work several times and he sounds very knowledgeable and professional.

I would like to solve the idle problem and this stutter problem so I can get this thing in for the clutch solenoid problem and make it pass inspection. It ran great right until the engine died when the IACV failed.

Sorry for the long post. Felt like a little history might help.

[rgk]

When you replaced the IACV, did you also replace the IACV gasket?

The ECU rebuilder I used stated that both the IACV and the TPS need to be replaced before re-installing the repaired ECU. I wonder if it wasn't your TPS that fried the computer.

Maybe take another look at the ECU?

[228920Pathfinder]

Thanks for the reply!
I actually had to buy two IACV to get the right one for the fix. The ECU fix required a Hitachi IACV be installed to match the OE unit. I had purchased a BDM(?) brand from OReillys before I read about that part of the deal. The OReilly IACV came with a gasket. Unfortunately when I got the new Hitachi IACV there was no gasket so I ordered it through the dealership where the vehicle was being "repaired". Used the VIN to place the order but the parts lady still got the wrong one (needed the 2001.5 type gasket but she ordered the 2001.0 gasket). Anyway, $4 later I had a new gasket and they ate the other one since it was their order mistake.

Basically, I used the instructions from a lot of posts on this forum to go about trying to get this running and so far I can make it run but not idle and it has that flutter at 1750 RPM.

I did replace the TPS along with the IACV when I installed the rebuilt ECU. I have tried more times than I can count to do the relearn procedure but the engine needs to be able to idle to complete that and mine doesn't idle. I have also done the TPS relearn with the pedal push and the key-on key-off part. This is really aggravating.

I am considering popping the case on the rebuilt ECU open to see what I find. It voids the warranty on the work done but the thing hasn't worked since so I don't think it matters now. I found a link in someone else's post to the chips and have that saved. I tried to find one of those chips before I sent it off but had no luck. Don't know how I messed that part up. Anyway, a few minutes with a solder iron may allow me to replace the chip myself. I'll do that if I need to.

Want to get this thing running. It was always the most dependable vehicle and nearly maintenance free. Ridiculous how one design decision renders a vehicle useless if you don't catch it in time.

I managed to get the vehicle to start and idle the last time I messed with it by using a spacer under the throttle at the throttle stop screw. I found by trial and lots of error that a .032 spacer (the thickness of a small ziptie as it turns out) would allow the vehicle to start and stay running at about 900 RPM. Unfortunately even doing that I couldn't get the idle relearn to complete. This method effectively opens the throttle a very small amount off of the closed position.

I have cleaned the MAF sensor (before I replaced it); and cleaned the throttle body and one of these days I'll stumble on the perfect fix.

[228920Pathfinder]

I am able to idle the engine now. I was messing around with it just working through various RPMs to see if I could find any other RPM where the idle fluttered. I was able to get the vehicle to idle as low as 250 RPM by carefully varying pressure on the accelerator pedal. After I did this I was reading thru the manual reviewing the idle relearn and discovered my foot was completely off the pedal and the vehicle was still running.

It turns out that if I very slowly let off the pedal after I start the vehicle (by giving it some gas as I turn the key) it will idle at 412-425 RPM with timing shown at 15 deg according to my Actron scantool.

I haven't been able to complete the relearn because part of it involves removing the brown connector while the vehicle idles (at 700-800 RPM I presume) and I can't get it to just idle at that speed unless I have a foot on the pedal and I'm not Rubber-band Man so my arms can't reach the connector anyway. LOL.

I suspect I may be close to solving this part of it. I just need to double-check the clearance on the TPS with open and closed throttle to make sure it is correct in range. I already know that the resistance on it and the IACV are good.

I also wound through a bunch of old photos and found a couple of the IACV connector that I took at disassembly last year. One of the pins appears to have some deformation/melting in the plastic around the slot. I don't know whether this happened when the ECU blew or whether one of the dealer techs used a blunt pin to try to test the circuit. I am planning to check this a little more thoroughly to be sure a good connection is made between the connector and the pins on the IACV so the ECU gets all the info it needs.

I'll load some pics of some of this if anyone wants to see them.

[228920Pathfinder]

I have been running this thing for a while now today and I can add that it does idle but only at 375-400 RPM. This means that it won't start using only the key, you have to give it some gas to start it and ease off of the accelerator after it starts until it settles around 400 rpm.

I also checked for the surge fluttering at about 1750 rpm that I saw yesterday. That is now disappeared. It idles smoothly across (at least) the range from 250 rpm to 4000 rpm with only the slightest flutter noticed between 1800-1837 rpm (scan tool numbers there).

Things I did today include:
Get in vehicle with scowl on my face (nearly permanent by now.)
Crank it by giving it a bit of gas as I turned the key and holding the pedal to keep it running.
I held the pedal at about 1000 rpm until the temp gauge on the dash showed it was hot and then attempted the relearn knowing it would fail at the "arms too short" part because it wouldn't idle.
After the relearn failed I attempted the same thing several times because though I am not a smart man, I am persistent and undeterred by failure.
Bored of the repetitious failures and convinced that there might be something else to test I decided to attempt to replicate the idle flutter noticed yesterday at about 1750-1550 rpm. I increased speed to that range and couldn't duplicate it. This led me to test a wide range of engine rpms to determine whether it moved to a new range or was absent entirely.
I began testing at 4000 rpm and moving slowly thru the range decreasing as I went to see whether anything funny happened. Nothing amusing to report. The vehicle ran smoothly thru the whole range down to 250 rpm. To get that low I had to very gently ease off of the pedal so as not to kill the engine. That's when I discovered that the thing would idle. Once I got to 250 rpm it picked up and held speed slightly higher and the SES light came on.
Since I had a SES light and a scantool I checked the code and found a P0505 IACV code. The thing was running fine idling at 400 rpm at the time so I just messed with it a little while longer holding it at various speeds as before. I couldn't get anything bad to happen so I cleared the code with the scan tool and eased back on the pedal and let it idle.
I continued idling the vehicle for 30 minutes or more or maybe I have a short attention span. Anyway, I decided that part of the problem may be in the TPS setting so I got my feeler gauge to check that.
Using the feeler gauge and after slightly loosening the screws on the TPS I set the .002 shim in at the throttle stop and verified continuity. Then I set the .006 shim in and verified lack of continuity. It initially had continuity with the .006 shim but I carefully rotated the TPS until I lost it and then tightened the screws to hold that position.
With a very large smile on my face and the full foolish thought that I had solved this problem I got in the vehicle and hit the key to start it.

Reality bites sometimes and I probably still have the marks from it. Somewhere.
I couldn't get it started unless I hit the gas. Once it started though it idled just fine at about 387 rpm.
I decided to let it run for a bit so I did. While it was running I figured I might as well try to road test it.
I eased it into gear and headed off into the unknown hoping that it would run long enough to get me back home because it was almost time for school buses to be running and getting trapped behind one of those on a rural highway can be a pain when your vehicle has an issue that requires you to keep your foot on the gas.
What a pleasure! For the first time since that last time I was running down the highway at genuine highway speeds instead of simulating it in the driveway. I drove that thing almost crazy but really only about 13 miles along rural and in-town streets and roads and found that it didn't die at all even coming into traffic lights where I had to stop. Instead, it idled along at 375-387 rpm waiting patiently for the light to green up.
I pulled back into the driveway and headed for the working-on it spot where it sits to this day.

During the test drive I didn't get any SES lights (scan tool was connected during the drive). Everything seemed to operate normally, except the obvious idle problem and the inability to start without hitting the gas part.

I guess I'm at a loss as to what to do now. I can't do the relearn because I can't make it idle near the correct rpm and I can't start it unless I hit the pedal and hold it while slowly letting it idle down or the engine dies right off.

Any ideas?

[228920Pathfinder]

Made one more stab at this thing starting with a cold engine this time.

On cold start (key turn and give it the gas and hold as it starts then back off slowly till it idles) the idle speed was 362 rpm according to the scan tool. Cold engine. Could barely hear it running though the tach clearly showed ~300 rpm.

Idled it until it was nearly warm and then accelerated through a wide rpm range several times allowing it to settle at idle. With engine nearly at operating temp the idle speed was 400 rpm.

Accelerating like that set a code and the SES came on. P0505 Idle Control System Malfunction.

Definitely need to verify the connection from the IAC connector to the PCM/ECU at the one pin where the deformation is noted. If not there then maybe try to unplug IACV and see what codes I get.

...

[228920Pathfinder]

Went ahead and tested running it without the IACV connected.

To do this I cleared the P0505 code from the previous run.
With engine off I disconnected the IACV connector.

I started the engine (now warm ~170 deg) and it idled as "normal" at 400 rpm. Ran it for about 10 minutes with this disconnected looking for any new codes. There were no codes set during this run. I accelerated through idle to 5000 rpm several times settling it back into idle each time and still had no new codes set.

I killed the engine and reconnected the IACV.
Engine warm and I started the vehicle with IACV connected and settled into an idle, again at 400 rpm. I idled the vehicle for several minutes and walked thru a wide rpm range settling back to idle each time. After idling for a few minutes the SES light came on again with a P0505 code.

I'm gonna double-check the quality of the connection at the IACV connector in the morning on the one suspect pin and if I can document that it is good then I'll order a new IACV.

I suspect the connector right now since the IACV tested normal with the multimeter when I reassembled everything yesterday. ~22 ohms across each pin pair. (1-2, 2-3, 4-5, 5-6). That is within spec on all. I will also recheck this tomorrow.

Done for the day. Thanks for watching!

[rgk]

P0505 suggests that your ECU is bad. Open it and inspect the black plastic rectangular pieces that stick up. If they are melted or distorted, the board is damaged. Sorry to say so, but the shorted ECU probably fried your new IACV.

Read this: http://www.justanswer.com/nissan/7e5d2- ... error.html

For future reference, the idle relearn on a 2001 does not involve the gas pedal. Check out this link for the correct procedure: http://nissanhelp.com/diy/pathfinder/pr ... arning.php

[228920Pathfinder]

>P0505 suggests that your ECU is bad. Open it and inspect the black plastic rectangular pieces that stick up. If they are melted or distorted, the board is damaged. Sorry to say so, but the shorted ECU probably fried your new IACV.

Like this one - Burned IC on Pathfinder ECU

That's what my ECU looked like after the original problem. I had it rechipped. If I had been able to find a chip myself I would've done it myself and saved the money. I also bought another ECU from a different rebuilder when the dealership manager told me that my rebuilt one (with the new IACV) didn't fix the problem. They swapped the second ECU into the vehicle and still could not get the idle relearn to complete. This is with a new Hitachi IACV installed with the rebuilt ECUs.

I will be opening both of the ECUs that I have on hand tomorrow to inspect them for any problems. Since there has been no burned smell noticed with either of them in the vehicle I don't believe that I will find any problem with either ECU. I may be wrong. It wouldn't be the first time.

I actually read a LOT of posts just like the one you linked before I ever decided this was something I could do myself last February when this thing toasted itself. I had investigated the potential causes and costs to repair and spent a lot of time on these forums investigating. I also downloaded the complete service manual from here to guide what I was doing since I had been working from a Haynes type manual before. I've been back and forth through the whole thing and in the process have done pin-outs and functional tests on things I never wanted to touch. I might be a better man for it but I'm a bit disturbed that I've never had to do anything at this level to maintain my other vehicles.

At the time I had 3 VW diesels, a Passat with 59k miles, a Jetta wagon with 274k miles, and a Beetle with 193k miles. With the present TDI troubles we no longer have the Passat. I also had this Pathfinder that has 228k miles. In addition I have two old Broncos, a 92 with 280lk miles and a 75 with 300k+ miles. I've been around mechanical stuff for a long time and I get my money's worth from everything we buy. The only vehicles in that list that don't run and drive right now are the Pathfinder and the 75 Bronco which is waiting for a full rebuild.I also traded an F250 Crew diesel in on a 2002 Supercharged Xterra when it hit 200k miles and needed a second dual mass flywheel within only 50k miles. That was too much for me. I got rid of the Xterra when it had 12k miles because it only got 11 mpg with my foot in it on the highway. I traded it for the Jetta wagon. Good trade if you consider I went from 11 mpg to 44 mpg immediately.

>the idle relearn on a 2001 does not involve the gas pedal

I have to disagree here because you have to have the vehicle idling while you pull the brown connector from the TPS. My vehicle wouldn't idle until today without someone having a foot on it so it was not a one man job to do the relearn. Even today part of the reason that the relearn won't complete is due to the fact that the vehicle idles so low that when you make it to the part where you have to rev the engine several times to make sure it idles okay the engine will die effectively terminating the process before it is complete. Every step requiring the engine to be started also requires a foot on the gas in my vehicle right now.

I totally agree that most of that relearn is just key on key off and the ECU harvesting voltage values from sensors to serve as reference values. It also does require the user to hit the gas though to verify the correct rpm and to use the gas pedal to maintain engine rpm while it warms up if it won't idle on its own like mine.

The last dealer tech struggled with this relearn using the Consult system and never got it to idle correctly. At various times he had it idling ~1500 rpm but not lower without getting it to relearn or he had it failing to idle at all and unable to relearn using both ECUs and new IAC, MAF, TPS.

Neither tech ever checked the PCV valve which must work normally for this to complete. I replaced that myself after I retrieved it from the last dealership finding that the original one was probably never replaced in 228k miles. It was nearly completely blocked.

I will check the ECUs that I have tomorrow to make sure that they are good. I will also check the pin in the IAC harness since it is not in the best shape as I tried to describe earlier. If this connection is not good then it doesn't matter whether the ECU or the IAC or the TPS works right, nothing good will happen. It may actually produce a short between a good IAC and a good ECU if the connection is intermittent.

This is my IACV connector - Damaged IAC connector on Pathfinder

I really appreciate that you've taken the time to review my posts. Thanks!

[228920Pathfinder]

I'll post pics of my ECUs when I crack them open tomorrow in case anyone is interested.

[rgk]

Your idle shouldn't be so far off prior to the relearn that you have to press the gas pedal. Either your IACV is shot, or your throttle body is damaged. Also, the code tells me your ECU is shot. You will likely have to replace all three again (IACV, TPS, ECU). Check the TB for proper alignment and operation while you are at it.

[228920Pathfinder]

I really appreciate that the message doesn't change. I've got some rain falling out here right now so I may not get on this today but I will definitely have your advice in mind as I proceed since I know you've been there with the same problems I've got now.

A question about throttle body damage - how do I spot that? I installed it with a new gasket between the throttle body and the intake and made sure all intake parts are installed and secure. Is there a way that it can be misaligned? I've never seen any of that mentioned anywhere.

Also on the throttle body - I cleaned it using CRC throttle body cleaner while it was out of the vehicle if I remember right and may also have run some cleaner through it while it was running after reinstalling.

There is also the likelihood that one or more of the techs who worked on the vehicle at the two dealerships cleaned or messed with (cleaned) the throttle body or other parts without mentioning it. The last tech told me part of the delay in getting my vehicle fixed was in waiting for a similar vehicle to come in for service so he could swap "known good" parts onto mine to help troubleshoot the problem. Pretty funny since he actually owns a 2001 Pathfinder himself and when I originally took mine in for service at that dealership he half-heartedly offered to buy mine since mine was in much better condition and better maintained (his description).

I had considered that something bad may have happened to it while cleaning it but don't have a good idea about how to determine whether it is damaged. What can you add?

Another question - If I pin-test all the components (IACV, TPS, ECU) and they pin-out good based on ranges/values documented in the manuals then I have no reason to replace those parts, true?

Thanks pardner!

[rgk]

The best way to test the TB is to get a used one and put it in.

Don't bother with pin testing. You won't be able to recreate live conditions. Check your ECU and go from there.