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

I forgot to send your pictures of manifold area close to the #3 or#4 Injectors - sending now.

Thanks so much for your reply!
I forgot to mention that this pickup truck is a 1996 SE Model - Changeover model built in 02/96 so many parts are different than models built prior and conforms to California, EPA and US emissions. Also, ECU does not throw any codes and there is no check engine light unless I unplug a MAF sensor, IACV, etc, and then it will come on and throw a code and or codes like P0100, 110,171,300,301,304,505. I clear the codes and they do not come back.
My code reader test of I/M Monitors as follows:
Misfire - okay Fuel sys - okay Catalyst Mon - INC, HTD Catalyst - N/A, Evap Sys Mon - INC, Sec Air Sys - N/A, A/c Ref Mon - N/A, OS Senor Mon -INC, EGR/VVT SYS Mon - INC.

Code reader during run monitoring shows OBD2 Sta = CA and VIN # states not available for this model along with the other readings.

Tests completed
1) Fuel Pressure (trying to maintain Idle due to surge, stumbling and trying to stall out) was at or a little above 34.
2) Few seconds after Ign off it read 43
3) Fuel Pressure Regulator Test - I was somewhat confused with instructions but using a hand pump type vacuum tool as I recall the fuel pressure did decrease as I pumped the tool as I was to keep it from stalling out. This old man may have to redo the test - need 4 hands on this issue -LOL.

Question 1) do you thing the IAC-AAC valve could be defective even though soaked and sprayed cleaned with carb/injector cleaner and then later with seafoam?
Question 2) ST FTRM Readings lock in at +25 at and above above 1,000 to 1,400 RPMs but come down below - could 02 sensors be defective even though I get readings
Question 3) The PCV was very hard to get to, but it did manage to remove and replace the valve (Had to remove tire, oil filter to get to it). IT did have fluid in the hose as I disconnected it but was not able to check the other end of the hose for cracks etc.
Question 4) Where do I hook a Vacuum gauge to the engine for this test?
Question 5) Could the Coil in the Distibutor be weak or bad distributor
Question 6) ECU Reset or replace as last resort

I will try to do a compression test in a couple of days and get back to you.
Thanks,
LWRoos

Tests completed
Fuel Pressure
1) Fuel Pressure (trying to maintain Idle due to surge, stumbling and trying to stall out) was at or a little above 34.
2) Few seconds after Ignition off it read 43.

Fuel Pressure Regulator
The fuel pressure did decrease as I pumped the Vacuum tool connected to the Regulator and engine vac plugged off.

Vacuum Test
Using a T connector, I connected the vacuum tested to line at base of throttle body area and disconnected the MAF sensor to maintain RPMs at about 1500 to 1600 instead of fighting to keep it from stalling out. Read at a steady 19.

Compression Test
CYL 1 = 155
CYL 2 = 150
CYL 3 =168
CYL 4 =109

Notes About Cylinder 4: My rental compression tester had a short extension and was very hard to connect so I don't know if it had a great seal but let's assume it did.
This truck is my nephew's. Don't know much about its history before he asked for help. When I was removing the Spark Plugs, I noticed #4 plug did not seem torque down as tight the others like too easy to break away as removing. I think this one and possibly the second one had been installed cross threaded before. While installing #4 plug it had sort of a wiggle to it at first and as all of the plugs it seemed like it took more than normal turning of plugs before they bottomed out. I was able to torque them all at specs 14 -20 lbs.

I will check to see if #4 loosens up after it is able to idle. Any suggestions? Should I use some bolt tight or the like if it is an issue.

OBD2 Readings
Disconnected the MAF sensor and took some readings as it idled smoothly in Park but at about 1,500 - 1,600 RPMs and in drive it will idle about 938 RPMs smoothly - when I drive it it spits, jerks etc, at about 2,500 RPMs.

MAF Disconnected P0100 and check engine light on readings all under stopped conditions.

MIL Status ON = both in Park and Drive
Fuel Sys 1 = Closed then changes to open1 both in Park and Drive
Fuel Sys 2 = N/A both in Park and Drive
Cal Load % = 28.2 to 40.8 in Park and 42.0 in Drive
Coolant (F) = 185-189 in Park and 192-194 in Drive
ST FTRM 1% = 1.6 to 25.0 (mostly 25.0) in Park and 0 to 5.5 in Drive
LT FTRM 1% = 0 in Park and -2.3 in Drive
MAP (HG) = 8.0-8.3 in Park and 12.4-13.0 in Drive
Engine Speed = 1513-1638 in Park and 938-983 in Drive
IGN ADV = 15.0-16.0 in Park and 10.0 in Drive
Veh Speed = 0 for both
IAT (F) = 129-142 in Park and 136-140 in Drive
MAF (LB/M) =.03 in both Park and Drive
ABSLT TPS % = 0 in both Park and Drive
O2S11 (V) =.72-.93 in Park and.77-.94 in Drive
ST FTRM 11% = -7.8 to -25.0 (mostly 25.0 in Park and -5.5 to.83 in Drive
O2S21 (V) =.87-.94 in Park and.04 I Drive
OBD2 Stat = CA for both - I guess this means it is a California Emissions type Vehicle

Yesterday after my last message I decided to go ahead and install a new IACV-AAC in case the valve motor wasn't working. I disconnected the battery for a couple of hours before install.

It did not help much - little to none but it did try to idle a little longer at first - LOL.

Then I drove for about 25 miles - mixed city and highway driving - hoping the ECU would make adjustments to correct but to no avail.

The engine light did not come on but as I mentioned earlier it never does unless I unplug something.

This morning I remembered to check for codes and P0171 was stored and of course no engine check light so I do not understand why the engine light does not appear for this 1996 truck when a code is stored unless I unplug a sensor or something.

P0171 Freeze Frame Info I discovered this morning from my driving yesterday after installing the IACV:
Fuel Sys 1 = CLSD
Fuel Sys 2 = N/A
Calc Load % = 31.0
Coolant (F) = 187
ST FTRM 1% = 0
LT FTRM 1 % = 0
MAP (HG) = 16.2
ENG Speed = 2300
VEN Speed = 41

Thanks Kenny.
Regards Larry

Hi Kenny,

Thanks for your reply!

I will disconnect the O2 sensors Tomorrow and get back to you.

I forgot to mention while driving after installing the IACV I noticed the Temp Guage was not working on the instrument panel (only time it happened).

While inspecting under the hood over the last 3 weeks of messing with this truck I was unplugging different connections and checking for a good contact and I noticed probably a coolant sensor electrical connection at the sensor was loose on the sensor after unplugging it (you could actually swivel it some left to right).

So, I got out of the truck during the above test drive and checked the sensor and swiveled it a little left and the instrument panel gauge was working when I got back in the truck.

Would this coolant temperature sensor affect anything causing the PO171 code? The gauge has always worked as I keep a close eye on the gauges while working on a vehicle. This was the only time, and I figured while installing the IACV I must have rubbed against it causing it to lose connection - lol. It definitely needs to be replaced and put on my to do list.

Other than this the only noticeable items while inspecting the truck was a ground strap connected to the firewall was not connected to anything so I connected it to the head of the engine and the intake may be missing a bolt that I mentioned earlier.

I must mention that the truck was broken into, and the radio system was stolen. They cut the wires to the radio and cigarette lighter under the dash. Also, a variable on/off/dimmer dash light control switch was stolen or lost due to the theft. There are no vacuum lines as the heater and a/c controls above the radio area are electic controlled. My Nephew states the truck ran fine after the theft and this issue started much later.
Thanks,
Larry

Hi Kenny,

Clearing the codes using the scanner (I did not disconnect the battery) and unplug the o2 sensors Failed the test as the engine still will not idle. Pretty much the same once the rpm falls below 1000 - 1200 or so it starts stumbling, surging and quickly comes down and finally stalls out below 500 rpm.

I did get codes PO135 & PO141 then later code PO130 But not a code for 02 Sensor Circuit Malfunction (Bank 1 Sensor 2).

I even drove it after it reached 178 F temperature - mixed city and Highway then got more gas - lol - sure using gas pretty fast.

Check engine light came on after the 2nd or 3rd start cycle. Had to go to bathroom - LOL.

Scanner reading as follows:
Freeze frame for PO130
Calc Load% = 52.9
Coolant (F) = 75
ST FTRM 1% = 0
LT FTRM 1% = 0
Map (HG) =17.7

After Engine warm up trying to idle it before and after driving it as follows:
MIL Status = ON
Fuel Sys 1 = open1
Fuel Sys 2 = N/A
Cal Load % = varies 38.8 - 41.2
Coolant (F) = got it up to 180
ST FTRM 1% = 0
LT FTRM 1% = 0
MAP (HG) = varies 22.7 +/-
Engine Speed = tried to hold at steady 1100 at idle after driving
IGN ADV = varies with rpm10 - 19
Veh Speed = 0
IAT (F) = varies 104-120 +/-
MAF (LB/M) =.1 - 2.0 +/-
ABSLT TPS % = varies with rpm 3.5 - 5.1+/-
O2S11 (V) =.3
ST FTRM 11% = 0
O2S21 (V) =.3
OBD2 Stat = CA for both - I guess this means it is a California Emissions type Vehicle

Do you think it could be the coil system built-in to the distributor? I did notice a member with a similar issue stating he and another member changed their distributor correcting their issue.

You mentioned ECT what is the definition, so I can look for the part to see if it is the one I was speaking of.

Thanks,
Larry

PS: This truck is driving this old man nuts - LOL!

Vacuum Test.
Using a T connector, I connected the vacuum tester to line at base of throttle body area and disconnected the MAF sensor to maintain RPMs at about 1,500 to 1,600 instead of fighting to keep it from stalling out. It read at a steady 19 as per one of my messages to you on 5/22. I must add to my earlier message that at the lower rpm the gauge was jumping all over the dial at lower rpm with the MAF connected. Maybe you could give me instructions on how and where to place the vacuum gauge if I did it wrong.
Sometimes I have sent you a couple of replies on the same day to try to give you additional info. Sorry if I am not communicating properly with you. Please review my messages as I also sent Fuel Pressure, fuel regulator and Compression test etc.
Thanks for your help!
Larry

Thanks for your reply! I will attempt this as soon as I can get some help and send you a video.
Larry

Hey Kenny,

Last weekend I installed my aftermarket IACV and both wires tips are the color of Red just prior to the pin connectors so thinking it didn't matter I hooked it up. Now I wonder and don't know if I screwed up in case one of them is supposed to be a hot wire and the other one a ground wire or link to the ECU. My old unit was the same way except the color was black on both tips. Neither units have any markings on the wires or pin connectors. Of course, it didn't fix this idle issue but if it is hooked up wrong maybe the IACV is not functional?

Please advise me if I should switch them at the connectors.
This weekend with some help I will get you the video of Vacuum Test a different RPMs.
Thanks,
Larry

My IACV wiring question was about hooking up both wires tips to the connector plug. I understand one should be power when IGN Key on and the other communicates with the ECU.

The new IACV I installed wires have red colored tips on both and my old IACV has Black colored tips on both wires. Neither have any kind of marks showing which is a positive or negative lead wire. So, I assumed it didn't matter and hooked it up. Now I am wondering if the valve is not working or working in reverse. I can't find any info on the internet nor from any sellers, so I thought I'd ask you.

This truck also has a Air Charge Temp Sensor (aka: Intake Air Temp, Air Cleaner Tempe) in the air filter compartment instead of being incorporated in the MAF sensor like newer autos. Claims are that both can cause stumble and surge and stalling. Very Confusing.

This issue is that the engine runs well at normal city and highway driving but at idle in any gear it stumbles and surges and quickly stalls out.

ST Fuel trim at +25 while driving but when at falling to idle fuel trims sometimes drop as low as +1.6 or so when it starts to stumble, surge and quickly stalls out.

I will send a video of the Vacuum gauge to you over the weekend.

Here's a pix of the IACV Valve.

No, the problem is when in Park, Neutral and in Gear it stumbles, surges and stalls.

The problem I am having is that the two wires on the Old and New IACV have no markings as to which go to power #2 pin or ECU Signa #4, so I do not know if it is hooked up backwards or if it even matters - LOL. None of the aftermarket sellers seem to provide this information on the wiring of the valve.
Larry