Minor fluctuations to RPMS while idling. Is this normal? Tune up? please help

[jasindude1]

I have a 94 4Runner its new to me, 241K on the clock, the air filter has been replaced the oil just changed by PO. I noticed while in line for at a drive-thru that about every 45 seconds there is a slight fluctuation in the idle, by looking at the gauge, i have the idle set at 750 (per tach), it will drop to as low as 500rpms and then go back to 750. The AC was on so i thought it was that, but when the AC was off it would do the same thing but wound drop as much. is this a normal thing? or should i be looking at other things? I figured it was too like clockwork to be fuel, maybe spark? Timing? Or maybe clogged injectors? The truck runs fine, never feels like its gonna die, just a little shaky when it drops RPMs, but then evens out. I wanted to get suggestions before just throwing parts at it. My idle is set at 750, is that too low? any suggestions would be greatly appreciated, I am about 5300 feet above sea level and i only put the cheapest fuel as this is my around town vehicle. Thanks in advance!

 

[jross20]

Mine has very small "jumps" up and down but maybe like less than 25 rpm I guess. I think that is normal.

Dropping to 500 doesn't sound right to me... Have you cleaned the mass airflow sensor? What kind of fuel economy do you get? Has it changed over time?

 

[jasindude1]

The RPM fluctuation was just an estimate when looking at the tach, I haven’t done anything to the 4Runner since I got it. I will look at the MAF this evening, I put some seafoam in the tank today on the way to work to see if it was just a clogged up injector, havent noticed anything tho but only drove like 15 miles.

 

[thennen]

Are you running the A/C? Or perhaps defog/defrost is on and the A/C compressor is cycling? If so, it's supposed to idle up when the compressor kicks in. Not sure what Gen3s have, but my 1988 had an "Idle-up VSV" or Vacuum Switching Valve. Its job is to bring engine speed up a little at idle to prevent stalls when the A/C clutch energizes and provide enough RPMs to the compressor. That failed once and caused similar symptoms.

 

[Pyral]

Mine idles around 1000, and it will drop to 900 when the AC turns on. This is a 3RZ. The year you gave makes it a 2nd gen, those came with 2 engines in the US: 3vz V6 and 22RE l4.

Have you checked the air filter. If its super dirty it could be restricting air.

 

[gamefreakgc]

First thing that should be asked, is it just the gauge moving or do you hear the engine dropping to a lower RPM and then raising back up to a faster one?

The 3VZ-E and 22-RE engines operate on the OBD-I system which behaves much differently than the 'newer' OBD-II. There is very little data you can view beyond reading voltages on a multimeter. Since there's basically no data we can look at, I would suggest a full tune-up and replace any maintenance item than has not been done. Pull the plugs, pull the wires and the cap and rotor off the distributor. Looks new and sound? Keep it. Test the components you can with a multi-meter or ohm-meter using the resistance setting. Anything out of line? Replace it. See if that clears it up. Definitely sounds like a misfire.

 

[nissanh]

TPS is the culprit. My 92 corolla did it too! Get an OEM Throttle Position Sensor.

 

[jasindude1]

The air filter is new, the gauge moves and u can feel the car shake, I think it’s only when the compressor cycles tho. My idle is set at 750, is that factory? The gauge shows a drop to the line below that’s then kicks back up. It has kinda evened out a bit, I’m thinking there prob was a clogged injector, I’m now at about half a tank and it seems to be a little smoother and not dipping that low just a little bit but not enough to “shake” the truck like before. I’m gonna run another fuel treatment after this one and make sure they are clean. I’m gonna check the TPS tho, bc I still get minor fluctuations when the AC isn’t on a well but they are really minor don’t even notice it unless I’m idling for long periods of time.

 

[HiLife]

Try cleaning your throttle body bore. Pay attention to the area were the throttle body butterfly seats against the throttle body. Make sure that area is free from carbon and oil that's blocking the gap inbetween the throttle body and butterfly.
Pull the ecu fuse, or disconnect the battery for a minute to reset the computer and force the ecu to learn how to idle again.

 

[spartacus]

The air filter is new, the gauge moves and u can feel the car shake, I think it’s only when the compressor cycles tho. My idle is set at 750, is that factory? The gauge shows a drop to the line below that’s then kicks back up. It has kinda evened out a bit, I’m thinking there prob was a clogged injector, I’m now at about half a tank and it seems to be a little smoother and not dipping that low just a little bit but not enough to “shake” the truck like before. I’m gonna run another fuel treatment after this one and make sure they are clean. I’m gonna check the TPS tho, bc I still get minor fluctuations when the AC isn’t on a well but they are really minor don’t even notice it unless I’m idling for long periods of time.

Cleaning the maf or replacing an old maf with a denso unit wouldn't hurt. Throw in a a new pcv valve while you are at it.

 

[Endlessblockades]

Cleaning the maf or replacing an old maf with a denso unit wouldn't hurt. Throw in a a new pcv valve while you are at it.

My 2nd Gen didn't have a traditional MAF sensor. The OP is in the wrong forum unless he made a typo

 

[spartacus]

My 2nd Gen didn't have a traditional MAF sensor. The OP is in the wrong forum unless he made a typo

Thanks, yeah my suggestion is for 3rd gens.