Engine will not idle, it stumbles and surges and quickly stalls

Hi Kenny,

I switched the wires on the IACV and installed a new fuel pressure regulator but no difference at idle but seemed a little crisper on Highway driving.

So far from my research through internet articles and videos I began chasing parts which is not good due to very limited funds.

I have new parts in this order such as: New Air Filter, New PCV, New MAF, Ran it out of gas on purpose for fresh fuel due to it setting for a few months because my nephew had no money for repairs, New Fuel Filter, New IACV-AAC, New Distributor at a smoking deal, New Air Cleaner Temp Sensor ( aka Air Charge Temp/Intake Air Temp Sensor - LOL) and lastly New Fuel Pressure Regulator.

I had Midas Muffler check the Catalytic Converter, is okay.

I had it checked by an auto service company (my grandson in law father used to own the business and trained the current owner who has owned it 30 years +/- after grandson father passed on) to diagnosis it. They were extremely busy and had it on two occasions for 2 days and then 3 days over the last 3 weeks. He didn't charge me anything - he even installed the new Distributor and the ACT sensor for me but could not figure it out.

Although I think it probably needs a smoke test and a backflow test as I believe they only checked the vacuum on the EGR valve and didn't pull it for testing and checking to see if it is clogged?

I don't know what's left other than EGR full check out, O2 Sensors (but we disconnected, and it would not idle), MAP, Multifunction TPS, Throttle Body, Weak Fuel Pump at idle? (We tested the pressure at higher rpm - MAF disconnected, is okay), and all the other electrical controlled vacuum switching solenoid valves - swirl control valves - purge valves - one-way valves- etc, smog pump, ECU, etc.

Vacuum Tests Videos - one with MAF disconnected to warm engine up - read 19.5 - Then 2 videos trying to assist it from stalling out. Then 2 videos starting - not assisting idle. One after new fuel pressure regulator and driving 25 miles +/-. One next morning with cold start. 2 Pictures - vacuum Routing and engine/Catalyst info.

Hopefully, these videos will assist in Diagnosis - See Attached.

Hi Kenny!

Thanks so much for your assistance.

So, as I understand with the engine trying to idle but surging, stumbling and quick stalling out the vac test points an internal engine vac leak. Therefore, to a valve job due to bad valve guides and or valves not seating properly. Is that correct?

What threw me off is the engine seems to run normal at higher idle rpm and while driving at city and highway speeds but just won't idle at a stop without assistances due surging, stumbling and quick stalling. I cannot hold a steady idle rpm pressing the accelerator pedal below 1,000 -1,400 RPMs in or out of gear, LOL.

Also, the vacuum test with the MAF disconnected the engine seems normal and smooth but creates idle at around 1575 in Park and 938 in Drive the reading hold pretty steady at 19 -19.5.

Could a weak fuel pump also cause a similar issue? As I remember we had to try to maintain/assist idle when we did the test and do not remember disconnecting the MAF sensor to maintain speed.

Grasping at straws now -LOL.

So many Sensors, Regulators, Coils, etc, etc, point to this or similar issue.

I am sorry I didn't take the vacuum test properly the first time along with the fuel pressure and compression test. I can also see the importance of videos sent to you.

I did learn how to take videos on my phone - AirDrop them to my email - follow the link to AirDrop site - download to my computer and upload to you among all the other things I am learning from you.

Thanks so much!

Looking forward to hearing back from you.

Hi, this is my second reply today so please review the one above this one.

Looking through my replies I noticed that I did not explain things very well at times - sorry.

The videos I sent of the vacuum test were done with the MAF connected except the first one I had the MAF disconnected so I could warm up the engine and the Vac reading was pretty steady at 19.5. I did not do a vacuum reading in Drive at idle while the MAF was disconnected - should have - but we know the idle RPMs hold steady at around 938 RPMs.
All other tests have the MAF connected.

The engine runs fine and seems smooth to me at city and highway speeds but when it is time to stop at a red light in or out of gear is when it will not settle into normal Idle rpm and starts to quickly stumble, surge and stall out.

ST FTRM readings confuse the issue for me because with the MAF Disconnected they are as much as - 25 and with the MAF Connected they are mostly +25 - LOL

Cylinder 4 Compression reading I got by cranking the engine at least 10 revs were 40 + lbs less than the others. The service shop readings were 30 + lbs less on #4. I think I cranked more revolutions than he did - LOL!
Thanks,
Larry

Hi Kenny,

Aside from the low compression issue I think my idle issue may be related to the MAF sensor.

I drove the truck to a Nissan dealership for a free inspection as they were not very busy after the Memorial Day Holiday and would look at it right away.

I drove it there with the MAF disconnected just so it would idle at a stop. Within 30 minutes I was told my MAF was bad, and they would have to order the venturi as the MAF is built into it from the factory and the computer doesn't like the aftermarket MAF units. Parts suppliers use the Venturi Part number to market a new MAF - LOL.

So, I drove probably 10 t0 15 miles and a couple of hours later I decided I would return the Replacement MAF (this one was the 2nd new replacement I tried) and I would put the old one back in until I could order a different and more expensive Nissan/Hitachi MAF.

When I took it out of the Venturi the MAF had a liquid substance on it - clear maybe a little brown color to it and putting my pinky finger into the ventrui mounting hole the liquid was the same feel and look. Can't tell if it's oily or coolant type of fluid.

Even from me driving about 5 to 7 miles back home and letting it set for a couple of hours I would think that if the tech sprayed the MAF sensor thru the port atop of the ventrui it would have dried by then.

I put the original MAF back on and started the truck and it idled for about 25 minutes in Park and In Drive/Reverse. Idle would fluctuate at times. I drove it and it tried to stall a couple times at stop lights.

What do you think about the liquid on the MAF. I am wondering if it is a Venturi or complete Throttle Body or bad gasket between them.

Regards,
Larry