Weird idle/surge?

[RylerTust]

So my horunna is acting a little weird. It's more annoying than anything. Weird idle. It'll surge and drop. And hasn't idled right in the past few days. Normally when It warned up itd idle at 1500 rpm and when warmed up itd idle at 750.

Now it idles at ~1200 all the time. And ONLY when fully warmed up the idle will drop and raise over and over. Rev it and it'll go away for a second. Them come back. Only under idle. Under load and acceleration it's gravy. When I use the a/c it's worse. Normal fan and heater don't affect it. Any ideas?? This is pissing me off.

90t4r
Sr5
5speed
22r-e
236k miles
A/c
P/s
4x4

 

[ToyoTech]

start checking all your hoses for leaks. i been saying alot to check the idle screw o ring only because i have seen this cause idle issues. could be low on coolant or air in system.

 

[RylerTust]

start checking all your hoses for leaks. i been saying alot to check the idle screw o ring only because i have seen this cause idle issues. could be low on coolant or air in system.

I sprayed MAF sensor cleaner on all the vacuum lines. No change in idle. It got kinda bad on my way to work this morning. Still only on idle. But it was every time I idled now. Not as intermittent.

 

[RylerTust]

start checking all your hoses for leaks. i been saying alot to check the idle screw o ring only because i have seen this cause idle issues. could be low on coolant or air in system.

On break right now at work. Checked coolant. It was low. That can cause weird idle??

 

[92-SR5]

On break right now at work. Checked coolant. It was low. That can cause weird idle??

On these trucks it can.

 

[illzoni]

The ECU on the 4Runner will cut ignition if it senses braking while under acceleration. So, if it's idling too high and the ECU thinks it's accelerating, when you brake it will drop RPMs. Once the RPMs are lower, the ECU will release and idle will surge back to the previous level. Rinse. Repeat.

The easiest way to confirm this is to idle without applying brake. If it doesn't drop and surge, you've confirmed the ECU is cutting the ignition. Then you need to fix what's causing it to idle too high, but at least you'll know why it bounces.

HTH,
Jon

 

[fourwd1]

On break right now at work. Checked coolant. It was low. That can cause weird idle??

Yes. If the coolant level is low, the EFI coolant temp sensor may not always have physical contact with the coolant, and could send erratic signals to the ECM.

 

[Tinman1985]

Head gasket could be on its way. Same thing happened to a buddy on his 22re.

 

[RylerTust]

Head gasket could be on its way. Same thing happened to a buddy on his 22re.

Eh. Head was just replaced. About to fill it up on coolant. Hope this helps.

 

[Gerdo]

The ECU on the 4Runner will cut ignition if it senses braking while under acceleration. So, if it's idling too high and the ECU thinks it's accelerating, when you brake it will drop RPMs. Once the RPMs are lower, the ECU will release and idle will surge back to the previous level. Rinse. Repeat.

The easiest way to confirm this is to idle without applying brake. If it doesn't drop and surge, you've confirmed the ECU is cutting the ignition. Then you need to fix what's causing it to idle too high, but at least you'll know why it bounces.

HTH,
Jon

Interesting.
My 3rd gen does, and has been doing this for months now.
Something I noticed is the the butterfly/linkage on the throttle-body has some play in it. It feels like it catches open a touch. if I, by hand, move the linkage around, while the engine is running, the idle settles down.

 

[tor-redneck]

theres also a small coolant line to the right of the throttle body, hooks up down near the thermostat. mine did what your describing and after tryen every thing it turned out that little fitting the hose is hooked to was clogged. if i remember corectly you can unscrew it like a bolt and then clean it out. that fixed my issue.....

 

[RylerTust]

Fixed! Topped off coolant and adjusted idle to perfect. Timing is now perfect and loping stopped. I think it was too high of an idle after I cleaned my TB. I just got this thing a few months ago. po must have adjusted Idle and timing without cleaning out all of the tb first. Dono if it was the coolant or the idle adj but its good now. *knock on wood. Thanks for the help guys. My guess is it was the previous advice about the idle being high and the brake cutting ignition and causing the surge/lope. Thanks guys!

 

[RylerTust]

Fixed! Topped off coolant and adjusted idle to perfect. Timing is now perfect and loping stopped. I think it was too high of an idle after I cleaned my TB. I just got this thing a few months ago. po must have adjusted Idle and timing without cleaning out all of the tb first. Dono if it was the coolant or the idle adj but its good now. *knock on wood. Thanks for the help guys. My guess is it was the previous advice about the idle being high and the brake cutting ignition and causing the surge/lope. Thanks guys!

 

[fourwd1]

Glad you got it fixed :cheers:

It's nice when it's simple.

 

[mikebontoft]

yes low coolant will do that. same as my mazda of that era... if the coolant is low, it may not fully submerge the sensor tip.... which tricks the engine into "warmup mode" and idles higher. Now that it idles higher, coolant flow is greater and a constant submersion occurs and drops the idle down again.