Symptoms:

If I start the car when cold, it starts and runs fine.
If I shut it off and restart it right away, it runs fine.
If I shut it off after getting it hot, then wait 10-30 minutes, it will start fine, backup, go into gear and sit there just like normal. When you start to load it, it coughs and sputters. Like someone choked off the air. Blipping the throttle has no effect, so I don't think it is the TPS. It appears to be time dependent. It will carry on for 30-45 seconds, then gradually clear up. Sometimes it will totally stall out. But restart right back up in neutral, you can rev it up fine, but if you put it in gear and start to go, it will die again and sputter. Then clear up and run fine, like I said, 20-45 seconds later.

I'm baffled. It throws no trouble codes (assuming all codes would trigger the SES light).

I have replaced the fuel filter, covered the computer to keep it from getting wet from the rain channel dumping on it from the windshield (what a dumb f'in design). I am putting plugs and wires on it this weekend, but I doubt that is it. If it were things like that, it would do it all the time and not clear up and run fine. This seems like something computer/software related. In the first few minutes on a warmed up car on restart, what is the computer doing? Is it in closed loop, testing stuff? Then switches to open loop right away because its already warm?

I also replaced the Idle Air Control Valve ($75!). I was convinced this was the problem, but nope.

If it were the MAF, then it would do it all the time right? Coils acting funny when they are hot? O2 sensor? What should be my next step (other than plugs and wires this weekend)? I hate to take it to the dealer, they are going to rape me and I am the type that doesn't like anyone monkeying with my car, yet I don't want to get killed in the car when it stalls. It is predictable though. Always on restart after its been hot and sat. Once it clears up, your fine.

Any help greatly appreciated and thanks in advance. Help!

 

Anyone think it might be fuel pump?

 

I would definatley do a fuel pressure/volume test.

 

Turns out it was the passenger O2 sensor. Just thought this might help someone chasing a similar problem in the future. Weird how it would only do it when hot after sitting for 10-20 minutes, then only do it for 30 seconds then be fine.

 

Ok, I'm bummed. I thought I had found the problem since it finally stalled one day and threw a code. I went down to Autozone and they read the trouble code and said it was passenger O2 high value. So I put a new O2 in that side and it ran fine for 2 days. Today I drove it to the store, parked, came out, backed up, and then it stalled again. Only does it when hot, and sits for 15-30 minutes. In the morning, when its cold, it runs fine. After it cleans itself out, it will run fine when hot.

To date I have replaced:

plugs, wires, fuel filter, pass O2 (do the driver also since it has 50k on it?). I had a fuel pressure gauge on the fuel rail and ran the gauge up onto the hood. I warmed the car up, turned it off,let it sit for 20 mins, then took it out and bam, it stalled. The pressure never fluctuated though. I don't think it is fuel pressure related. Could it be the computer? TPS? If its TPS, why wouldn't it do it all the time?

What's my next move? I hate to take it to the dealer, they will rape me.

Jason

 

I think a scan tool or atap would be very benifical to you, find someone local who can help ya out, other wise your just throwing parts at a problem.

 

The code scanner that Autozone ran said it was the passenger O2. Could it have been wrong? What sensors does it look at when its in cold startup and switches to warm mode?

Anyone in the York, PA area want to help me out with a scan tool? Thanks

 

Might want to replace both of them. Even though you threw a code for one side doesn't mean that the other is bad. Believe me I have been through numerous o2 sensors so far and each time I have to replace both of them.

 

SCAN TOOL!!!!!!!!!!! Throwing parts randomly is not the way fix a problem its a way to blow money.
"Is it in closed loop, testing stuff? Then switches to open loop right away because its already warm?"

Cold engines start in open loop, and once warm if every thing is within specs it will enter closed loop.

OPEN LOOP - the A/F ratio is controlled to provide the best driveability and minimal emissions under the following conditions:
A. Start-up - richer mixture
B. Cold engine operation - richer mixture
C. Acceleration - richer mixture
D. WOT - richer mixture
E. Deceleration - leaner mixture or complete fuel cut-off (EFI)
F. Idle > some engines
G. Heavy engine load - determined from TPS & MAP or MAF

CLOSED LOOP - the A/F ratio is maintained at an average of 14.7 : 1. This ratio allows for the best catalytic converter operation and the least amount of tailpipe emissions during the following conditions:
A. Idle - EFI and some carbureted engines
B. Steady cruise

TYPICAL PCM FUEL CONTROL MODES
Closed loop can only be attained when the engine has reached a minimum temperature (120oF - 160oF), the O2S is hot and operating and the open loop timer has expired (time depends on start-up temp.).
During extended light load cruise conditions the PCM may enter a
semi-closed loop mode and command an A/F ratio of 16 :1 or leaner to improve fuel economy.

1. Shut down - system voltage below 9v or engine speed less than 200rpm. In this mode the computer does not control anything.
2. Start-up Enrichment - provides a rich fuel mixture for a short time after any engine start. The length of time depends on coolant temperature.
3. Open loop - During engine warm-up the fuel mixture control is based on inputs from all sensors except the O2 sensor. The length of time open loop lasts depends on coolant temp., O2 sensor temp. and the open loop timer. Open loop occurs at every start-up.
4. Closed loop - After the timer has expired and the engine and O2 sensor have warmed up, the ECM uses O2 sensor input to fine tune fuel control. The system remains in closed loop until a change in load occurs or the O2 sensor cools off. If a change in load occurs the ECM adjusts fuel delivery accordingly, ignoring the O2 input. The O2 input is only used during idle and cruise conditions.
5. Enrichment or WOT - If the throttle is opened to near WOT the ECM controls fuel delivery at full rich.
6. Cranking - throttle less than 80% open.
A/F ratio 1.5:1 at -33oF, 14.7:1 at 202oF (EFI)
7. Clear Flood - throttle more than 80%,
A/F ratio 20:1or leaner. (EFI)
8. Battery voltage correction - if battery voltage gets too low the ECM will increase injector pulse width to make up for slower injector and fuel pump.
9. Fuel cut-off - key off, no rpm signal to PCM. (EFI)
10. Limp-in - uses back-up program stored in a RAM to keep the engine running in the case of an ECM failure.

FMEM - Failure Mode Effects Management - the PCM substitutes a working value if a sensor fails. (FORD)
Most EFI systems have similar strategies.

 

I'm really tight and I don't know any shops in the area that can do a scan. The autozone scanner found no other codes. Does that mean the O2 maybe didn't need replaced?

From what you wrote, it appears my car is staying in closed loop. When I go to put a load on it, it should switch, but for some reason it isn't. Seems like coolant temp is a recurring theme in the equation. Replace that next? Is that the sensor that is near plug #1? If that sensor was give false readings or none at all, would it throw a code? Is there a way to test the water temp sensor? I assume you have to drain the entire system to change that.

Anyway to check to see if its the maf? Will the car run without the maf hooked up? Would that be a good test?

Thanks for your help, I will be printing that out and keeping it. Do you have a list of all the sensors, they're ranges, and what mode they are being used?

 

"I'm really tight and I don't know any shops in the area that can do a scan. The autozone scanner found no other codes. Does that mean the O2 maybe didn't need replaced?"

I understand this, but if you buy parts you dont need, you could have used that money on the scan.

"From what you wrote, it appears my car is staying in closed loop. When I go to put a load on it, it should switch, but for some reason it isn't. Seems like coolant temp is a recurring theme in the equation. Replace that next? Is that the sensor that is near plug #1? If that sensor was give false readings or none at all, would it throw a code? Is there a way to test the water temp sensor? I assume you have to drain the entire system to change that."

If you have a multi meter, you can test any sensor on the car, even a cheap one (digital) can be had for about 10$ and will do what you need it to.
To test a coolant temp sensor, get the car to operationg temp and shut if off, un plug the sensor and use you multimeter on the ohms setting.
degrees k ohms
-40 100.7
40 7.5
100 1.8
210 185

You can also verify that the sensor voltage is between 4 volts (very cold) to around .5 volt when the engine is fully warmed up. Room temperature will usually produce 2 to 3 volts (approximately 1/2 of the reference voltage)

It could throw a code it might not.
No you dont have to drain the system, just chage it real quick on a cold
motor.

"Anyway to check to see if its the maf? Will the car run without the maf hooked up? Would that be a good test?"

Engine will not run with the maf un hooked.

Thanks for your help, I will be printing that out and keeping it. Do you have a list of all the sensors, they're ranges, and what mode they are being used?

Yes but not here Ill post it later.

 

I ran a bunch of diagnostics on the car and we didn't find anything out of range. Everything looked good and ofcourse I couldn't get the car to stall when we were watching it. Grr! Could have been because the temperature was pretty warm here in PA this weekend. I have no idea what's wrong. We thought maybe it was the EGR valve sticking, but I'm not sure. I swapped in a stock maf and it still does it. So its not:

fuel pump
maf
plugs
wires
fuel filter
tps
water temp looked ok
map looked good
o2's looked good
timing was fine
short and long term trim looked normal

what's left?