1999 2.7l stalls when slightly warm

My '99 Tacoma stalls when slightly warm. Manual tranny, 4wd, Xtra cab, 2.7 l 4 cylinder engine. It starts OK when cold, and it runs OK when fully warmed up (idle is a little rough). The RPM's dip a bit when I decelerate, but normally this does not lead to a stall. Only when the engine is slightly warm does it stall when I come to a stop.

When I try to restart it after it stalls, it is difficult to start, and judging by the smell, I believe it is very rich at this point. It is similar to a carbureted car with the choke on.

The catalytic converter was stolen about 4 years ago, and replaced with a relatively cheap one. Not sure if this would have anything to do with it.

There are no engine modifications. Not much has been replaced on this truck. Mainly I just change the oil and filters (air and oil) and tires when they wear out. Fuel filter is too hard to reach, so I haven't changed it. Mileage is around 180k (going from memory). I bought it new.

I am thinking, maybe it could be some kind of temperature sensor? How does the ECU know when the car is warmed up? Does it use the coolant temperature?

I don't know if the RPM's dipping is the same problem, or a separate one. If you know what might cause that, I would appreciate feedback on that, too. But the stall is my biggest concern right now.

Thanks for reading.
--McKenzie

 

Have you checked to see if the ecu is throwing any codes?

 

The check engine light is not on. I was assuming that the check engine light would be on if their were codes. Maye that is a bad assumption? What is the easiest way to check for codes?

--McKenzie

 

Usually it'll throw a CEL. But might as well get it checked. Any local auto parts store should be able to scan it for free (ie: advance auto)

 

Have you checked the valve clearance? May be to tight, and causing compression loss after warming up.

 

With a multi-meter, check the resistance of all the temp sensors, to see if they are within spec. On my truck, one of the temp sensors is the intake air sensor, which is built in to the MAF sensor, so I'm not certain is a resistance check of that would be valid.

 

Many problems like this are due to dirty, sticky, slow, or faulty Idle Air Control (IAC) valves. I had all kinds of weird stalling and hot start problems and a rich smell like you describe. Basically it controls the amount of airflow into the mix (around the throttle plate) to add extra air when the motor is cold. I cleaned the filthy IAC valve and it made it better, but it still stalled sometimes. I replaced the IAC valve, and it hasn't stalled since.

 

Thanks, all. I will look into air intake sensor (or air intake / MAF sensor), and idle air control valve first. If googling does not shed light on how to find them, I will be back and post follow-up. I also have a mechanic who will probably connect the scanner for free, so I will try that. The truck is getting old but I have no plans to sell it, so I am not opposed to replacing stuff on it. I think checking the valve clearance would be more of a last resort type of thing. And the truck runs OK when it is fully warmed up. There is a mid-range temperature, not cold but not fully warmed up where it behaves funny.

 

I'd check the codes as stated. Did this start suddenly ??? Then I'd Change gas stations, try a higher grade and you might consider that if it throws no codes Cleaning of the MAP sensor and possible the injectors - but at my last self fix. Then I'd see what it would cost for a diag / quote at the Dealer.

Although it "possibly" could be the valves, I'd think that if that was it, and the engine runs OK cold - I'd think it would be worse when warm ...??