Corolla intermittent loss of engine power

[TechTim]

I have a 1990 Corolla, 1.6 liter, 5 speed, 190K miles, regular maintenance including timing belt replacements. Runs top notch most of the time, but I have a very sporadic intermittent loss of almost all engine power, but you can keep driving and it goes away after a few minutes. This only happens a couple times a year, but when it does it's nasty. It has done this for the 5 years and 45K miles that I have owned this car, but it has recently gotten worse.

It happened again last night while my son was driving home from work. The problem starts without warning. He had to pull over. The engine will start and rev rough, but even letting the clutch out in neutral is enough to stall the engine. He had it towed home, but later in the evening it was running fine again.

I have replaced the fuel filter, plugs/wires/cap/rotor, air filter. Battery/alternator are newer. The only consistent condition that he and I have been able to notice is that this seems to only happen when it is a little cold out (about 40 degress last night) and after it's been running for a little while.

Appreciate any feedback. I'm thinking maybe O2 sensor next. Also a trip to Autozone to get the computer read.

Tim

[TekPhobia]

Intermittent problems have to be the hardest thing to diagnose.

My immediate thought is that it's running REALLY rich. It's doubtful the O2 sensor would cause this; wouldn't cause it to go so rich that it barely runs.

The easiest way to pull codes is to short Te and E1 on the diagnostic connector (attached to driver's side fender, labels are under the cap). The codes will blink out a digit at a time separated by a pause. So, a code 12 would be *blink*....*pause*.....*blink*blink*.

So, we've got a few possibilities: MAP sensor, THW (water temp sensor), TPS and the cold-start circuit.

The TPS on that motor is just a simple switch for WOT and idle. If it sticks on idle, then you'll get very little to no power. But...shouldn't stall the motor upon letting the clutch out in neutral.

A Hayne's manual should tell you how to test THW and the MAP sensor.

The cold start injector is controlled by a thermostatic switch. If that fails for some reason the CSI is stuck on...instant rich.

I'd try and get my hands on a service manual and go through the troubleshooting steps.

Also, let us know what codes you pull...


-Tim

[Pineapple]

Bad wire, lose connection, bad coil, fuel pump, fuel filter, injector. Bad O2 won't shut the car down. Check for broken ground wire.

[TechTim]

Thanks for the quick feedback everyone.

Turns out that I likely have a bad MAP sensor according to the computer code (31). Kinda pricey replacement part, and needs to be ordered. Can't find anyone in the Raleigh NC area with it in stock. $160 at Autozone for a Wells brand.

Before my son orders this (it's his car), he is going to do some resistance/voltage checks. BTW, it is no longer intermittent. I told him that's a good thing, now we will know for sure when it's fixed.

[automatic]

I would try and find a low-budget wrecker and source the part used instead. I would almost always have a used oem part than a new off-brand part.
Old cars will eat you alive if you go new on everything.

[Deep]

Originally Posted by TechTim

Thanks for the quick feedback everyone.

Turns out that I likely have a bad MAP sensor according to the computer code (31). Kinda pricey replacement part, and needs to be ordered. Can't find anyone in the Raleigh NC area with it in stock. $160 at Autozone for a Wells brand.

Before my son orders this (it's his car), he is going to do some resistance/voltage checks. BTW, it is no longer intermittent. I told him that's a good thing, now we will know for sure when it's fixed.

Before you go out and drop 160 on one, check the vacuum hose that runs to it for cracks or kinks, I'm pretty sure its firewall mounted on the 4AFE.

[TekPhobia]

Let me know if you can't find one. I have a MAP sensor from my 4AFE that's just kickin around doing nothing...


-Tim