Engine stalling at startup

Hello out there,

Can anyone give me some reasons why the engine is stalling on startup. All of a sudden started to happen. No events that might be the cause. One day it was fine the next it's stalling out. Has been running fine since I bought it when I joined this Web Site. Cranks up fine , take my foot from the gas pedal and it drops off to 0 , engine conks out. I CAN keep it running by pumping the pedal. I thought it was because it was cold , but today it did not matter. Conks out hot or cold. Although never consistant. Sometimes it stays running the next deceleration and it conks out. Very puzzling. Anyway, would appreciate any ideas or directions.

Lou

 

What if any codes have you pulled ??

Always the first step.

Could be a few things without pulling codes it would just guessing.

 

MAF sensor maybe, try cleaning it recently or replaced? Check fuel pressure too, might have a fuel pump issue or clogged fuel filter

 

Does it idle rough when you are on the pedal?

 

MAF is also my guess. I'd check that connection and make sure it's seated properly. If not pull it and clean it with some electronic cleaner.

 

Engine runs smooth. No misfiring at any speed. Mass Airflow Sensor. I already replaced that a few months ago. Fuel pressure. Yes, how to check that ? Let me research the how to's. And what about the throttle position sensor.

What regulates the engine speed ? The engine should be slightly high on startup and then slow down as the engine warms up. Then there's the engine speed change when you turn on the A/C,

None of this takes place. Engine stays at same RPM as soon as I start it when I warm it up and nothing I do changes that idle speed.

 

Sticking/bad idle air control valve and/or dirty throttle body would be my first suspects based on your description of symptoms.
Get you some carburetor or throttle body cleaner and clean the throttle body and idle air control valve.

 

If it runs fine and just won't idle, it's likely the idle control valve IMO. My truck intermittently does the same thing and usually it frees up either with a hard rev or from the vibration of driving.

 

IAC. Clean it.

 

Also check your Coolant temp sensor

Any issues with the IAC every time that tripped A PO505 code on the ones I experienced.

 

I think it would only trip a code (mine doesn't) if there was a problem that the ECU could detect like an open circuit or short in the IAC wiring. The valve doesn't have any position feedback AFAIK so the ECU can't know if it's sticking or not.

 

Mine were tripped by the change in idle speed!

From what was normal

 

Idle speed codes take awhile before they will set, some vehicles will never set them. I've seen quite a few older Honda and Toyota cars come in with low idle/stalling problems, not one of them had an idle code. Quick cleaning of the throttle body and idle air control valve and they were good to go.

 

Hi,

Thanks for all the great responses. I cleaned the IAC a month or so after I bought the car because get this, I thought it was idling too high. Cleaned the throttle body. Could it be the Fuel Pump Regulator. Like I said, it sometimes acts up and other times it stalls out. I'm leaning towards something mechanical with a moving part that is sometimes in the correct position and then sometimes its not. Which would be that sliding plate in the IAC.

Lou

 

I do need to admit most all these issues were working out the bugs in 3.4 swaps. That had been given up on seen to have problems unable to be fixed.

I will agree I know I have seen strange things like anything electronic things can be within plus or minus 10% and still be considered within spec.

It is a given some will respond different.

 

Update as of today. This morning I changed out the ERG valve. The big disk with all the hoses attached iun the back. Cleaned some corrosion from the positive battery terminal. Cleaned the diodes in the MAF sensor. Now it seems to be idling at a steady 1000 when the engine is hot. Have to wait till morning to see if it stalls on start up. This is something I can live with. Stalling out after warm up is unacceptable. I did find a small nut and screw at the bottom of the throttle cable and put a business card in the gap and it did speed up the idle. That screw looks as if it was glued in place. There's some yellow residue all around it. I'm not messing with it for the time being but as far as a quick fix that looks to be an option. BTW , I did an OBD scan and no faults or anything else popped up. I did remove the negative terminal after I pulled the MAF since that causes a check engine light. I'll let you know how it goes. Persnickity cars but when their running right their great.

 

It's still idling too high; should be about 750rpm at operating temp.

The throttle body stop screw has paint on it to be tamper-evident and probably doesn't need adjustment anyway. The butterfly should be open only just enough to keep it from sticking shut. Idle speed is controlled entirely by the idle valve. It sounds like you have air getting in either through a vacuum leak or the IAC isn't closing enough.

 

I'll keep checking for vacuum leaks. I'll add some cleaner to the fuel and see if that does anything. At this point 1000 works for me. 750 is perfect. it was around 1200 before I started trying to get the RPMs down some.

The MAF sensor plays a big roll since the engine shuts down as soon as its disconnected. Makes me wonder if I have the correct sensor since it's such a critical part. Sensor could be reading and sending incorrect data. I'm tempted to put the old one back in and see what it does. Easy trade out.

These sorts of thinks take a lot of trial and error. Even when you have a fault. Fault codes as far as I can tell are pretty general. Like air fuel ,or misfire on 3. Sorta helps but there's no real specifics. In other words thanks for telling me what I already knew.

I am not pulling that IAC again. That thing was spotless when I put it all back together. At least not until everything easier is first resorted to.

 

Did you install an aftermarket MAF sensor? aftermarket sensors and Toyotas don't mix well, that's one area where sticking to OEM/Denso is pretty much the only way to go.

if it is OEM it might still be worth swapping the old one back in just to see what happens.

 

The latest update is that I started the engine and it seems to be okay for right now. Cranks up and runs at around 550 when cold then goes up to around 750 when it gets hot. Did not change out the MAF. I'll see how it goes for a while before I try anything else. Seems like the old saying if it ain't broke don't fix it might be applicable right now. Thanks for all the great feedback !!