98 RAV - What sensor is not working in open loop mode? No response to accelerator until car warms up

98 Rav4 (130,000 miles) starts fine, idles fine, runs fine for 30 seconds then the accelerator no longer has any effect. I can put the pedal to the floor, but there is no gas getting to the engine, it will idles but doesn’t go. Until it warms up to operating temperature and then it is just fine.

This gets worse the more times I stop for an hour then try to go again - it is better when it is starting from being completely cold.

The check engine light does not come on, two different mechanics have tested it - no codes are produced - the computer thinks everything is just fine. One of the mechanics called his buddies at a Toyota garage in California but none of the 12 mechanics there could figure it out.

I am located on the island of St John in the US Virgin Islands where we have very limited mechanical expertise so any help would be very much appreciated (who knows, maybe you would need to fly down to fix it in person!)

Geez, this sounds like a weird problem. First thing that comes to mind would be a throttle position sensor. I’ve run across some that haven’t set codes in earlier OBD vehicles.

Yes it is weird. According to TESTER’s answer from another question, there are 4 sensors involved:coolant temp sensor, the throttle position sensor, MAF sensor, and the crank position sensor. Each costs hundreds of dollars o replace. How can I test each one? Or is there a better way to approach this?

My guess is the temp sensor. If it’s defective and the ECU thinks the engine is already at operating temperature, it’ll fail to bypass the oxygen sensor loop and will fail to run the engine rich. A cold engine not running rich won’t be fed enough fuel to accelerate properly.

This can happen without trippping a code. The temp sensor is not compared to any other signal and the ECU may not have any way of determining that it’s defective.

The good news is that it’s easily tested. Any shop can check the temp sensors output against spec. Well, any shop except perhaps the Toyota garage in California.

The other sensors are possibilities also, and they as well can be checked, but my money is on the temp sensor. My second guess would be the TPS.

We had a 95 towncar that had the same issue after my brother melted the air temperature sensor with quickstart. we replaced it and it now runs fine.

I’m trying to figure out where the open loop reference came from since there is nothing to suggest an issue with it.

If you’re pushing on the gas and nothing is happening - i.e. it just sits and idles - then the only thing that could mean is that the throttle plate isn’t actually opening up when you step on the gas.

The thing that would make the most sense would be an issue with an electronic throttle control - but I didn’t think they were being put on Toyotas as early as 1998.

Thanks everyone.
I will test the temp sensor first and report back.
Cigroller- The throttle is mechanical in the 98.

Most often the term “open loop” is a reference to the O2 sensors…Though it could point to others…most commonly that terminology is associated with the O2 sensors… they are also directly related to the fueling of the engine. They work in conjunction with several other sensors to determine the correct amount of fuel to inject into the combustion chambers.

The most prominent sensor in my mind would be the MAF sensor…without it the car has no idea how much fuel to inject and will also create they symptoms you described. In your instance it would be GREATLY beneficial to have access to the same vehicle in known working order to swap the sensors over from one to another to see which one it is without a massive financial investment…the next best thing is to gather a bunch of sensors from a vehicle in a salvage yard.

The thing you need to keep in mind first and foremost is that you usually CANNOT return these sensors when you buy them…so you need to know what you are doing when diagnosing these types of issues.

I still lean heavily twd the MAF… but like the guys state it can be many others… In order I’d say MAF, then TPS, Cam or crank angle sensor…etc… VEry hard to diag this issue via the net…as you can pickup many clues when you are in front of the vehicle…very rapidly you can rule many out within seconds… Where are you located?


The problem with thinking its a sensor - such as the MAF - is that if the throttle plate opened and the PCM didn’t know that it did b/c it wasn’t getting the massive increase in airflow info from the MAF, this would constitute a massive vacuum leak that would easily stall the engine. Its the same with something like TPS problem. If you hit the throttle and the car just continues to idle as if nothing happened then the throttle plate has to be closed. If the throttle plate opened the engine would do something. It would at least stumble significantly if not stall out.

We need a better description of what the car actually does when you step on the gas pedal. Someone could also easily put it on a scantool and watch what all of the sensors are doing.

I may have confused the issue my mentioning the open loop mode. Since the problem occurs during the warm up phase, I presumed it had something to do with that sequence.

I am located in the US Virgin Islands, on the smallest island, St John. The island is only 13 miles long and very hilly. There is only one place where I can get into 4th gear, and then only for seconds. Don’t know if that could be a factor. The car has lived here since 2004 and for 40,000 miles with very few problems.

A mechanic has the car and will be running tests over the next day or so. I will keep you all posted.

Thanks very much.

So when you press on the throttle it continues to idle smoothly, or does it stumble and cough and try to rev up?