1998 Rav4 ... Very low idle, intermittent stall

[HawkeyeScott]

Bought a 1998 Rav4 (auto, AWD, 2.0L, 105K miles) over the winter and with the weather breaking have started to do the typical new-to-me baselining. Pertinent to this post I've done plugs, wires, cleaned throttle body and idle air control valve, installed new fuel filter and run one can of Seafoam in the gas tank. The previous owner drove it as a back-up so it averaged about 1000 miles a year since 2018.

Issue: the car has a very low idle when stopped in drive. The idle seems to be slightly lower once the car has been driven awhile. I put the scan tool on it last weekend and warmed up it idles in the low 600s. My workaround has been to shift to N at stop light and the idle increases slightly - enough to avoid the low frequency vibration that shows up around 650 RPMs.

Besides the idle issue, It has also hiccupped under acceleration a few times and actually stalled under load on the highway last weekend. It immediately restarted. Fuel mileage is about 25 MPG commuting, so no complaints there. I have yet to see a check engine light.

Everything I am reading suggests these possibilities for essentially the same symptom: tired fuel pump, throttle position sensor, crank sensor, MAP sensor. I'm also wondering about aged vacuum lines.

Any suggestions on what to focus on next? Thanks a lot.

 

[rijndael]

The idle seems to be slightly lower once the car has been driven awhile.

Besides the idle issue, It has also hiccupped under acceleration a few times and actually stalled under load on the highway last weekend. It immediately restarted.

Do you have any misfires incrementing?

 

[HawkeyeScott]

Nope, no misfires.

 

[rijndael]

How are the fuel trims? LT and ST.

 

[Kira]

MAF...is it cleanable? Some appear to be sealed boxes while some are very open.
Also, some are both MAF and pycnometer (incoming air temperature) combination sensors.

Also, is a good dosing of Techron the same as Seafoam?
The PEA in Techron and other products is said to work on cleaning injector nozzles upon shutdown; so use it before a stint of local driving.

Can you measure fuel pressure at the rail? <goes to weak pump.

 

[Brian123]

Bought a 1998 Rav4 (auto, AWD, 2.0L, 105K miles) over the winter and with the weather breaking have started to do the typical new-to-me baselining. Pertinent to this post I've done plugs, wires, cleaned throttle body and idle air control valve, installed new fuel filter and run one can of Seafoam in the gas tank. The previous owner drove it as a back-up so it averaged about 1000 miles a year since 2018.

Issue: the car has a very low idle when stopped in drive. The idle seems to be slightly lower once the car has been driven awhile. I put the scan tool on it last weekend and warmed up it idles in the low 600s. My workaround has been to shift to N at stop light and the idle increases slightly - enough to avoid the low frequency vibration that shows up around 650 RPMs.

Besides the idle issue, It has also hiccupped under acceleration a few times and actually stalled under load on the highway last weekend. It immediately restarted. Fuel mileage is about 25 MPG commuting, so no complaints there. I have yet to see a check engine light.

Everything I am reading suggests these possibilities for essentially the same symptom: tired fuel pump, throttle position sensor, crank sensor, MAP sensor. I'm also wondering about aged vacuum lines.

Any suggestions on what to focus on next? Thanks a lot.

1) Get a new Idle Air Control Valve
2) Check the PCV

I kind of had a similar issue like what you were having years ago, I was having stalling issues, I cleaned the Idle Air Control Valve, and it was fine for a few days, then the issues started coming back. If you have a Mass Airflow Sensor, make sure you clean it off.

The stalling on the Highway would have me concerned.

The tired Fuel Pump is a thought, except I was always under the impression that a fuel pump either worked or it did not.

 

[Kira]

Wouldn't be unheard of to find an air filter box completely packed with nuts.

 

[97prizm]

Bought a 1998 Rav4 (auto, AWD, 2.0L, 105K miles) over the winter and with the weather breaking have started to do the typical new-to-me baselining. Pertinent to this post I've done plugs, wires, cleaned throttle body and idle air control valve, installed new fuel filter and run one can of Seafoam in the gas tank. The previous owner drove it as a back-up so it averaged about 1000 miles a year since 2018.

Issue: the car has a very low idle when stopped in drive. The idle seems to be slightly lower once the car has been driven awhile. I put the scan tool on it last weekend and warmed up it idles in the low 600s. My workaround has been to shift to N at stop light and the idle increases slightly - enough to avoid the low frequency vibration that shows up around 650 RPMs.

Besides the idle issue, It has also hiccupped under acceleration a few times and actually stalled under load on the highway last weekend. It immediately restarted. Fuel mileage is about 25 MPG commuting, so no complaints there. I have yet to see a check engine light.

Everything I am reading suggests these possibilities for essentially the same symptom: tired fuel pump, throttle position sensor, crank sensor, MAP sensor. I'm also wondering about aged vacuum lines.

Any suggestions on what to focus on next? Thanks a lot.

Not sure if it pertains to your vehicle but maybe the idle air control valve is bad? What about the shift solenoid?

 

[D60]

Nope, no misfires.

Based on absence of codes, or counts?

 

[carviewsonic]

I would clean the MAF sensor first, since only a can of MAF cleaner and ten minutes is needed. I just cleaned our K24 Accord's with 185,000 kms, and it idles a bit smoother now and feels more responsive to light throttle.

 

[D60]

I would clean the MAF sensor first, since only a can of MAF cleaner and ten minutes is needed. I just cleaned our K24 Accord's with 185,000 kms, and it idles a bit smoother and feels more responsive.

What I'm finding is that '98 is SD

But would be worth looking at live data for the MAP. I'd be curious about reading KOEO, at idle and at higher RPM

Also might be worth unplugging the MAP if it seems suspect and seeing how a drive goes.

But I also agree I'd like to see fuel trims. If it's dumping or pulling a bunch of fuel that gives a general direction

 

[iCurious]

This vehicle does not utilizes a MAF sensor, but instead a MAP.

Very possible the IACV is no good. Common problem on these Toyotas.

 

[D60]

This vehicle does not utilizes a MAF sensor, but instead a MAP.

Very possible the IACV is no good. Common problem on these Toyotas.

Would an IAC cause stalling on highway under load as reported by OP?

However, he could be facing two problems

 

[burbguy82]

My first thought is throttle body issue, or torque convertor issue, as the idle jumps back up in neutral. I am not a professional. How is the fluid level and condition? Cheap to check.

 

[iCurious]

Would an IAC cause stalling on highway under load as reported by OP?

However, he could be facing two problems

I missed that. This vehicle I believe has a distributor, I would look into that also.

 

[HawkeyeScott]

Update:

I had bought a cheap TYC fuel pump via Amazon ($22) and installed today. Figured it was worth it to diagnose and, if it was the pump, I'd have a backup once I get a permanent Denso. (The pump is accessible from the top and only takes about 30 minutes to change out.)

Once I had it buttoned back up and reconnected the battery, it fired right up and ran great. Even idled high, but I remembered the Toyota battery/throttle re-learn process takes about 5 minutes.

Decided to go for a drive. Ran really nicely for about 10 minutes. Idled at 9K RPMs at several stop signs. Thought I had it licked! Then, at a red light with a prolonged wait, the RPMs just kept dipping until they were back down to the low 600s, just like before.

So, it doesn't seem like it's a fuel issue, at least from the pump up past the filter.

Air filter box is spotless. PCV was replaced right when I got it. (Sorry, forgot to list that.) ATF was pretty good when I got it and I did one drain and fill a couple of weeks ago. Level is good.

I'll keep digging based on some of the questions and ideas above. Thanks again for the input so far. Much appreciated.

 

[D60]

Decided to go for a drive. Ran really nicely for about 10 minutes. Idled at 9K RPMs at several stop signs. Thought I had it licked! Then, at a red light with a prolonged wait, the RPMs just kept dipping until they were back down to the low 600s, just like before.

I hope not What's redline on these little things, Mr Days of Thunder?

 

[HawkeyeScott]

I hope not What's redline on these little things, Mr Days of Thunder?

Haha. Yeah, she would have been about 3k north of the redline at 9k.

I’ll blame the gas fumes for that one!

 

[Tkonrr]

Try giving the throttle body a good thorough cleaning. Too much crud around the plate will block off airflow at idle. Run a good fuel system cleaner like B12 Chemtool or one with a good amount of PEA to clear out your injectors. Lastly, check for vacuum leaks, a common problem with older cars.

 

[D60]

Vac leaks might cause problem(s) but typically speed density is very forgiving of vacuum leaks.