My engine stalls at low rpm - idle

Hello,

This definitely sounds a fuel system problem. I have included in the diagrams below a step by step troubleshooting guide for tracking down fuel system problems. Please go through it and let us know what you find out.

Thanks,
Alex
2CarPros

Thanks, i will try this tomorrow and get back to you. I am pretty sure the fuel pump is good. The truck will idle for hours with no problems. It is when it is shifted into drive or reverse and i hit the pedal that it gives me problems. I am hoping it is just a leaking injector.

Hello again,

I have a question for you. Is your Malfunction Indicator Lamp(MIL) or "Check Engine" light on?

Thanks,
Alex
2CarPros

It was, but the only codes it gave were for a MAF. Knock sensor vow volts. MAF is brand new. Just changed. And i am doing the spark plugs. Fuel pressure regulator and thermostat this weekend. That is when i am going to check the fuel rail and injectors. I know the MAF will cause sputtering if bad, but can a knock sensor do the same?

Hello,

Usually a knock sensor is used by the Power-train Control Module (PCM) a.k.a. "computer" to detect engine detonation, or "knock". This is very bad for an engine and comes about when your air fuel charge spontaneously combust without the spark plug igniting it. This can happen for a few reasons, but we will save that for another day. This ignition event happens when the piston is still traveling upwards on it's compression stroke and it literally slaps the piston, creating a loud noise that sounds like a knock. The knock sensor alerts the PCM of knock and the PCM will retard the ignition timing, thus pulling the cylinder away from detonation. This, probably is not causing your vehicles issues. The Mass Air Flow (MAF) Sensor on the other hand could cause all of your vehicle's problems. It measures all the air that engine is ingesting and along with the Intake Air Temperature (IAT) Sensor and provides this information to the PCM. The PCM uses this information to know how much fuel to add to the air for it's base line air;fuel ratio. What was the exact Direct Trouble Code (DTC) or "code" please? We can go from there.

Thanks,
Alex
2CarPros

Sorry i was at work earlier. The codes it gave were. P0102 (maf) u1301 data link hugh voltage bus shorted to battery. P0108 (map sensor) p0131 heated o2. And p0128 thermostat. I just bought both upstream o2. New thermostat. new spark plugs. I just changed the mass air and fuel filter. And cleaned the throttle body.

Hello again,

No problem about work. Okay let's take a look and see what we got going here. ok, I have included in the diagrams below a step by step troubleshooting diagnostic guide from the vehicles manufacture for DTC P0102. Please go through it and let me know what you find out. I have the same thing for all the other DTC's on your list, but I don't want to overwhelm you. We will go one at a time. Let us know what you find out.

Thanks,
Alex
2CarPros

Okay. So i changed spark plugs. Wires. Seems to be running better. Just when i turn the wheel to the left truck completely shuts off. Could this have been the problem in the first place?

Hello again,

Okay. I have included the diagnostics for the next code, which I believe to be the problem, DTC U1301. Please go through it and let me know what you find out.

Thanks,
Alex
2CarPros

Hey Guys, love the website. I have a 2003 CHevy Tahoe 5.3 Z Flex Fuel. Troube began with a CEL/SES light. Few days later Tahoe started idling rough, varying idle speed, and on cold start may die if left idling during warm up. On a cold start, I also notice occasional knock in the engine, and if I slightly rev engine or place in drive before waiting for engine to warm up, it is VERY apparent. At first, it would idle better after warm up, but now it idles rough regardless, however, the knock does go away after it is warmed up. Only codes it spit out are P0174, and P0171 bank 1 and 2 lean. I cleaned the MAF sensor, and didn't notice a significant change at all. Should I go after new MAF, new O2 sensors??? Thanks for your help.

Shayne J. Benoit
Spring Cityl, Tennessee

Start by checking for vacuum leaks that would allow extra air into the intake system (thus a lean mixture) Also, I would check the ambient temp sensor. If it is telling the computer it is warmer than it actually is, that will cause a lean mixture too. Usually when an O2 sensor or MAF is bad, they set their own code.

Let me know what you find.
Joe

Joe,

Any more specifics on the ambient temp sensor as far as location on viehicle. There is one in grill, but I think it feeds the rear view mirror thermometer.

[quote:1e138592e1="TnCajunNuke"]Joe,

Any more specifics on the ambient temp sensor as far as location on viehicle. There is one in grill, but I think it feeds the rear view mirror thermometer.[/quote:1e138592e1]

Could the ambient temp sensor also be called the Air Change Temperature Sensor?

See if this helps and let me know.

FYI, I discovered that the IAT (Intake Air Temperature) sensor I inquired about is integrated into the Mass Air Flow sensor on many Chevy's. The harness on the MAF has a Black and Tan wire that attaches to the IAT sensor. If this has failed, JET has a Intake Air Temperature Sensor Relocation Kit 61635 for 2003 Chevy Tahoe

equipped with a Mass Air Flow Sensor that has a Integral Intake Air Temperature Sensor. The Intake Air Temperature Sensor is a negative coefficient (NTC) thermistor that is used to sense air entering the engine. The computer utlizes the IAT to adjust the air/fuel ratio in accordance with air density. It's also used to modify spark advancement and acceleration enrichment. This kit allows the IAT to be relocated away from the hot engine compartment so the computer can get a more accurate reading of ambient air temperature thus improving performance.

My tahoe was parked for six weeks while out of town. When attempting to start it...it cranks and runs for a few seconds then stops. Battery is ok. Fuel filter was changed about three months ago. I have had no problems in the past with the car having any trouble starting on the first try. Some tell me it might be the fuel pump however fuel is present when checking the injector. Any ideas...

Test the fuel pressure confirm it whether its within specifications, then test the coolant temperature sensor and idle air control valve and throttle actuator control. This is common when you have a vacuum leak or the throttle bore needs to be serviced here are three guides to go over when fixing the problem.

https://www.2carpros.com/articles/throttle-actuator-service

and

https://www.2carpros.com/articles/stall-at-idle

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please run down these guides and report back.

ive changed my fuel pump and filter. when i crank truck it will crank and run for about a second and shuts off. i have not check engine light on. when it cranks it sounds normal, no jerking or spudering. doesnt sound like its misfiring.

You may have a short or some melted wires. Also you should check battery cables for clean metal to metal corrosion free fit.
I am giving you some diagnostic walk throughs to get you started and they are very helpful. Advance Auto or Auto Zone will test just about anything, pull codes for free and loan you test and specialty tools. Just use the links below;

https://www.2carpros.com/articles/engine-stalls

I dont have a check engine light on. Can i pull codes with out light on? My battery died and the truck sat for 3 weeks before i got a new one once i replaced it has not ran since. I had no problems before that. My battery went died because i left my lights on and it was an old battery. If wires were melted which ones or were should i start looking? Also someone told mee it could be my crankshaft position sensor. If so would check engine light come on? Or if distributor was bad?

You can have a trouble code without the "Check Engine Light" coming on.
You may not have melted wires but if you do you will be looking in the starting and charging circuit. I am attaching wiring diagrams.
It could be a bad position snesor. I believe that gets talked about in the diagnostic walk through.

When battery died, it is equivalent to disconnecting the power source and that would result in computer losing memory. This would result in idling and performance issues. Try feathering the gas pedal to see if the engine continues running.

Feathering the gas is not an option to keep it idling it won't stay run longer than a second. If I do pat the gas it shuts off quicker. When I pat the gas it will only crank and not run for a second.

That means it is not an idling issue.
More like an MAF problem.
Check to see if there are any trouble codes stored.

Just finished up an entire crankshaft swap on my vehicle listed above. Everything is connected in place and accounted for. Now when I go to start it up it shuts off after releasing the key once it fires up. It has spark. I hear the fuel line kicking on. And i have plenty of oil pressure. Yes, it has a full tank and all fluid levels are where they need to be. What else could I have overlooked?

Can you get a recording of what it sounds like when you are starting this? This could be a couple things so hearing it will help narrow this down.

Then we need to check for codes just to be sure we have none as that will cut down the diagnosing time.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Lastly even though we hear the pump, we need to check pressure while this is starting and then we will need to check to see if the injectors are cutting off by using a noid light.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

I attached all these guides that will help with figuring this out. Basically I thinking there is an issue with the crank sensor and the PCM is cutting the injectors off so we need to prove or disprove that.

Thanks

SUV listed above starts but stalls. any suggestions on what could be problem?

Hi,

Listening to how it is revving up and down, the first thing I suspect is a faulty idle air control valve (IAC). The IAC is what is responsible for maintaining idle speed.

Here are the directions for replacement. However, before getting a new one, remove the old one and make sure there isn't a carbon build up in the throttle body and on the pintle. Also, if you have someone turn the key from off to on, you should see the pintle move.

___________________________________

1997 Chevy Truck K Tahoe 4WD V8-5.7L VIN R
Idle Air Control (IAC) Valve Replacement
Vehicle Powertrain Management Fuel Delivery and Air Induction Idle Speed/Throttle Actuator - Electronic Service and Repair Procedures Idle Air Control (IAC) Valve Replacement
IDLE AIR CONTROL (IAC) VALVE REPLACEMENT
Throttle Position Sensor Electrical Connector

pic 1


pic 2


pic 3


pic 4



REMOVAL PROCEDURE
1. Remove the electrical connector from the Idle Air Control (IAC) valve
2. Remove the IAC valve attaching screws.

CAUTION: If the IAC valve has been in service: DO NOT push or pull on the IAC valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also, DO NOT soak the IAC valve in any liquid cleaner or solvent, as damage may result.

3. Remove the IAC valve assembly.
4. Remove the O-ring.

CLEANING AND INSPECTION PROCEDURE
1. Clean the IAC valve O-ring sealing surface, pintle valve seat, and air passage.

^ Use the carburetor cleaner and a parts cleaning brush in order to remove carbon deposits. Follow instructions on the container.
^ Do not use a cleaner that contains methyl ethyl ketone, an extremely strong solvent and not necessary for this type of deposit.
^ Shiny spots on the pintle or seat are normal. They do not indicate misalignment or a bent pintle shaft.
^ If air passage has heavy deposits, remove the throttle body for complete cleaning.

2. Inspect the IAC valve O-ring for cuts, cracks, or distortion. Replace if damaged.

NOTE: If installing a new IAC valve, replace with an identical part. The IAC valve pintle shape and diameter are designed for the specific application.

3. Measure the distance A between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure in order to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

MEASUREMENT PROCEDURE

NOTE: If installing a new IAC valve, replace with an identical part. The AC valve pintle shape and diameter are designed for the specific application.

Measure the distance A between tip of IAC valve pintle and mounting flange. If greater than 28 mm, use finger pressure in order to slowly retract the pintle. The force required to retract the pintle of a new valve will not cause damage to the valve.

INSTALLATION PROCEDURE
2. Lubricate the IAC valve O-ring with clean engine oil.
2. Install the IAC valve assembly.
3. Install the attaching screws.

Tighten
^ Tighten the IAC valve attaching screws to 3.0 Nm (26 lb. in.).

4. Install the electrical connector.
5. Reset the IAC valve pintle position.

5.1.Turn the ignition switch to the ON position for 5 seconds.
5.2.Turn the ignition switch to the OFF position for 10 seconds.
5.3.Start the engine.
5.4.Check for the proper idle operation.

___________________

Let me know if this helps.

Joe

5.7 TBI, engine timing at 2 degress BTDC with brown wire disconnected.
Noid lights indicate the injectors are firing during start up. After the engine starts the engine stalls, the noid lights stop flashing, the injectors stop spraying.
12 volts at the injectors.
Fuel pressure good.
Fuses good.
Relays good.
ICM good (tested with appropriate test equipment)
Ignition pick up coil tested good.
Oil pressure sending unit good.
Continuity from both injectors to ECM/PCM harness connector, positive.
Continuity from ECM/PCM ground wires (pins A and B) at harness positive.
Continuity from ICM connector to ECM/PCM wiring harness connector positive.
Replaced ECM/PCM with identical unit as per Vin#.
Removed and replaced, IPC, ICV, IAT, TPS, MAP, Fuel Pressure Regulator and ignition switch at steering column/key in sensor checked to be in working condition.
Engine grounds to chassis and body checked to be good at multiple places.

The connector at the ICM has a red/blk wire that reads 1+ volts with digital meter key on, zero key off. I can not find a reference for this wire it is listed as Ground Circuit for ECM/PCM at the connector and as Ignition Control Module REF Low at the red ECM/PCM connector per available sources.
The engine starts on the first revolution and will run as long as fuel is dribbled into the TB. I am missing something but I don't know what it is.
At this point I am rechecking all the checks I have made and replacing parts I have already replaced.
I do not have a shop manual for this vehicle other than Haines or Chilton's which address basics and not in depth issues.
Any help or advice would be appreciated.

Zero Replies LOL I understand that.
Today the engine starts and shuts off just like it has done every day. The noid lights go out and the engine shuts off, the engine will run with fuel dribbled into the TBI the noid lights do not flash.

Sorry for the delay. When you updated the post it moves it back to the bottom of the list which is ordered oldest to newest so we were working on the older ones first.

Just so I understand, the engine starts and stalls immediately?

If this is the case the the injectors are being shut off as a way to cut the engine off.

The fact that you have 1 volt on the ground wire (lo reference) for the distributor could be an issue. I attached the info below on this wire. It is terminal A and is used to make sure there is there is a good ground.

Let's measure resistance on that wire from end to end with it unhooked from the distributor and ECM. It should be less then a half ohm.

Let's start with this and then we can start working through this. Clearly we just need to find why the ECM is shutting the engine down as it appears you have replaced everything involved so the ECM is getting a faulty signal somewhere to shut it down.

Have you checked for codes?

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method