i recently blew a bypass hose on my 93 toyota pickup an lost most of the coolant, had to remove the battery to get to the hose to be replaced! after fixing the hose problem and replacing the coolant and hooking the battery back up now i have an idle surge problem? not sure if i have air trapped in the system or something else is wrong any help would be much appreciated on this issue!

 

Does the surge happen as soon as you start the truck or only after it warms up? If it happens right away, it is most likely an air pocket in the idle air control valve.

If it happens after the truck warms up, then you may have a bigger issue if that temp gauge starts rising into the red...

 

It starts surging in idle after about 2 to 3 minutes into running, The temp gauge goes to about half way then stops never gets to the red in this time frame. Temp normally stays less than a quarter at idle when I drive it stays at a quarter or less.

 

Does the idle surging only occur, once it's warmed up some, when the brakes are applied, or all the time? If this is the case, the idle is set too high. Also, if there's air trapped in the Aux Air Valve, it could cause this problem by allowing too much air into the intake manifold.

Did you "burp" the coolant system when you got done with replacing the coolant? You can do it fairly easily by: Park the truck nose high. Either on ramps under the front tires, or just on a hill. When it's good and cold. Then ensure the radiator and recovery tank are properly filled. Put the radiator cap on, but loosely. Only to the first notch, not down tight. Start the truck, and let it run for 20-30 min. Let it good an warm. Watch the temp gauge to be certain the thermostat opens correctly.
Let it cool down again, and check the radiator and recovery tank again, ensuring both are properly filled. When you run it like this, all the air should go to the highest point in the system. With the truck nose high, that's the radiator cap. It will bubble out into the recovery tank, and thence overboard. This may leave the radiator and/or recovery tank low on coolant, because as the system cools down, it will draw coolant from the recovery tank back into the radiator. If the recovery tank runs low enough, it will allow air to be drawn into the radiator. Just add the 50/50 mix to them to the proper levels. Fill for the radiator is up to the bottom of the filler neck, up to the Full-Cold line in the recovery tank. If you have any doubts, burp the system 2 or 3 times. Won't hurt anything. might actually help.

Does this help at all?
Pat☺

 

Yup. That's what's happening with our first gen.

 

Generally, usually, normally, most often (getting the idea?), that's caused by nothing more than the idle being set too high.
Toyota figured there was no reason to have the engine spun up when you're slowing down. IE: The brakes are on, and the TPS is closed (idle switch closed).
SO, they built a feature into the ECU that cuts the injectors off if the engine RPM is above about 1100 or so when the brakes are applied. Once the RPM gets down to the "normal" idle range, the ECU allows the injectors to function again. If the idle speed is set too high, this circuit will cut the injectors, the engine RPMs drop down, the ECU allows the injectors to function, so the engine RPM comes up, the ECU cuts off the injectors, rinse, repeat.

Double check the engine RPM at idle, warmed up, TPS aligned correctly. If it's above about 800-900, adjust it down until it IS. Make sure the idle switch in the TPS is adjusted correctly, and that the idle adjust screw's o-ring is in good shape.

Hope that helps...
Pat☺

 

Low coolant can cause idle surge. If it happens when the brakes are applied, then that's because of high idle, and the fuel cut RPM is doing what it's supposed to do. Make sure you have a good o-ring on the idle adjust screw. My 92 was doing it randomly for about a year when the brakes were applied. Replaced the idle air control valve, and that fixed the problem. Specs below for fuel cut RPM.


• The vehicle should be stopped.
• Accessories switched OFF.
2WD A/T (stop light switch ON) Fuel cut rpm: 1,300 rpm Fuel return rpm: 1,000 rpm
Others Fuel cut rpm: 1,900 rpm Fuel return rpm: 1,600 rpm

http://htftp.offroadsz.com/marinhake...45fuelcutr.pdf

 

Thanks gents.
Mrs. fish has errands to run this morning.
When she gets back and the truck's all warmed up I'll get in to it
and spray a little carb cleaner around while I'm at it and check for leaks.

 

Iacv?

 

Idle Air Control Valve

 

It's running like a new car now. Thank You

 

Ive been looking up Idle surge issue for two weeks now and have tried everything mentioned on forums. How can I tell if my IAC is bad? When the truck is cold no surge only happens when warmed up and brakes are applied.
I know the issue has to do with RPMS being set to high, my idle set screw it all the way down and still have a high idle. A week ago I was able to adjust the idle set screw until the surge went away when brakes were applied but a week later problem came back.

- no vacuum leaks
- clean out IAC and throttle body
- replaced idle set screw O-ring
- check the IAC coolant lines for blockage.
- new radiator
- burped all air out of coolant system

 

When the truck coolant is fully warmed up, IE: the thermostat is opened, the IACV should be completely closed. Allowing no air through it and up into the throttle body. You could, for a quicky check-out, pull it's large air line off he throttle body, blocking both sides. The end of the hose, and the hole it feds into. This should tell you real quick if the IACV isn't closing all the way. If your idle drops down, it's not closing all the way, and allowing unaccounted for air into the throttle body. The ECM is expecting X amount of air, determined by the position of the afm vane. If the system is getting a lot more air than the ECM is expecting, as determined by the values the O2 sensor is sending the ECM, it will get confused. If the IACV isn't closing all the way, there's the source of the extra air.
Alternatively, you could just compress the hose with long-nose vice grips, and see if there's any change in the engine behaviour.

Also, you want to be certain that the throttle control valve, the large butterfly valve behind the TPS, is closing all the way when there's no pressure on the throttle pedal. They can get sticky as crud builds up on them over time. Some carb cleaner on the bearings on both sides of the butterfly, then a small shot of WD-40 can do wonders. IF it's sticky. When the cable is relaxed, you shouldn't be able to push the butterfly further closed.

Also, ensure the Idle contacts of the TPS close properly, thus letting the ECM know the engine should be at idle. If they aren't, you will have these troubles. The FSM will tell you which two contacts on the TPS plug are the Idle Switch contacts.

Another thing to check is the "Dash Pot". The small device on the throttle, where the throttle cable connects to the throttle body. It's essentially an open ended air valve, that allows the throttle to open as rapidly as desired, but the closing is delayed a few seconds. This keeps the throttle from slamming shut when the throttle is suddenly released, like during shifting gears, and so forth. if it gets sticky, it may not be allowing the throttle to close completely.

Does all my babbling help at all?
Pat☺

 

This weekend I resolved my issue with surging Idle after warm up. I replaced my idle control valve with a brand new one while throttle body was off I cleaned up the excessive carbon buildup on the throttle body and intake but I think the main issue was caused from a clogged IAC hose from thermostat housing to IAC. Now new cleaning of all the coolant lines, new coolant and new IAC the truck idle is back to normal and no more random temperature changes while driving on the freeway.

 

I need to tackle this, it’s been so long since I did all of the above but maybe I missed something. Mine has the surge but only when brakes are applied while warming up. I’m just used to it at this point but reading this thread kicked my OCD back in gear

 

This guy's video does a really good job explaining the idle control. Maybe it can help you out.

 

Ive been chasing this IDLE surging for a while since November 2021. When summer comes I adjusted my idle screw for the surge goes away. When winter comes I Have to re-Adjust my idle screw for the surge to go away. I have finally permanently solved the surging issue. I
recently replaced my throttle position sensor and adjusted it properly using LCE adjustment procedures. the truck has never ran or idle so smooth since Ive own it. Hope this helps someone else with the same problem.

things I originally replaced chasing the problem
- Idler air valve X 2
- all vacuum lines
- idle screw O-Ring
- VSV sensors
- all new heater and radiator hoses
- new radiator
​​​​​​- flushed and burped coolant more than once
- new radiator cap
- throttle body gaskets

 

The LCE procedure differs from the FSM? If so, can you copy & paste the LCE procedure? Thanks

 

https://lcengineering.com/part-1061042-1061043-1061044-1061045-1061046-1063034-1061039-throttle-position-adjustment-procedure/