Barry D

Brand new to site. Hello!

I need some help/advise. I have a 90 Toyota 4x4 Sr5 3.0 V6 manual trans truck. I am the original owner.... bought it new in 1990. Never, and I mean never a lick of problem in all those years. Now, I have that BS surging idle problem. I have read and read about the issue here and else where. Here is what I can tell you about the issue. Does not do it when it is first started. Driving it for a while and you come to a stop. It will randomly surge, meaning not at every stop. If you tap the accelerator it will stop. When it is not surging the idle seems high....maybe 1000-1100. Also, when you put the air on the idle will increase higher then it should, in my opinion. Had the a/c compressor replace and when I got it back the idle was higher then when I had the original compressor on the truck?

When I first noticed the problem I noted the coolant level in the reservoir was very low, bad daddy! I have filled it but it still is randomly surging when I come to a stop. I tested the break booster and it seems to be working properly and I can not find any vacuum leaks. I am thinking TPS because I can tap the throttle and it will stop the surging. There is no check engine light on and the truck runs good otherwise with good acceleration. Any body have any ideas that I can test?? Thanks.

350xrider

I'm experiencing the same issue. Once the engine is at operating temp, it idles at 800. However, when I drive and come to a stop it idles at 1,500 until I tap the throttle. I cleaned the K&N filter, Mass Air Flow sensor and throttle body. In addition to this surging idle issue there are times when the truck is very low on power and then all of a sudden surges with energy back to normal power. It reminds me of the power fluctuation when the A/C compressor engages but much worse. The distributer is new (about 10,000 miles) but I'm wondering if it could be incorreclty advancing the timing. Truck details: '94 3.0 5spd.

Barry D

thanks for the reply. I kinda sorta fixed the problem. It is still there just not as bad. I tuned down the idle. The TB is some how plugged w/ carbon and the air mix is off causing the truck to idle as if it has a vacume leak. The computer is shutting the gas off and you get the surge. I pulled the air screw out cleaned it and set the idle lower. When I cleaned the air screw it fit very loose and actually stated to turn itself clockwise as I dove it causing more issues. The air screw is part of the TB and you can not buy it. I ended up putting teflon tape on it and that solved the loose screw issue. I plan on running seafoam for several tanks of gas....have not done it yet... and see if that might clean the TB. I really do not want to take it off. Now when it surges, it is very low and I am living with it. The surging is not as frequent now as it was

Co_94_PU

iTrader: (-1)

Let's not confuse a sticky throttle with triggering a fuel cut off aka surging..

The throttle plate should have a crisp snap when released, like a mouse trap, otherwise it is binding somewhere. The first thing I would check is if you can lift the throttle pedal with your toe and it reduces idle. This would maybe be just a cable adjustment to put some slack in it.

While you are adjusting the cable disconnect the snap-arm to the throttle mechanism. Check for a crisp snap close, if it drags any it needs a good cleaning. If there is anything thick enough to chip or flake away you need to remove it for a good soak and cleaning I'm afraid. You can take the air hose off and verify the correct vacuum ports are showing on the front side of the plate, but probably over kill.

Now surging. The ECU will shut down if the engine rpm goes over 1800 while it is at an idle state(Idle contacts in TPS closed). It will switch back on when the rpm drops below the preset, its 12-1600 around there. So the rpms "surge" between these two rpms. It is always caused by a base idle being to high, and it triggers when you activate one of the idle ups, vacuum brake assist, power steering or AC idle ups. The easiest way to check this is to unplug the throttle sensor, by passing the idle contacts tricks the system, now press the brake pedal repeatedly and force the rpms up it should rev past 1800.

You get a good base idle by warming up the engine, jumping the diagnostic port, and then adjusting the idle screw to spec. Once you have base idle you should check the timing. They are interlinked so changing one effects the other and you may need to readjust them both, don't get to hung up on it being spot on and get stuck in a loop.

Now assuming you don't have any vacuum leaks you should have a cold idle of around 11-1200 that will drop to the 750-900 spec once warm. You will also have plenty of rpms to run the AC and brake while cornering.

Barry D

Thanks for the reply.

No, it is not a sticky throtle. There were no codes just a high idle. And yes you are correct after warm up if you turn the air on or press on the break it started the fn surging. I read for days, watched videos and ended up turning the idle down.... which seemed to help a lot but the problem still persists. Like I was saying after taking the idle screw out and cleaning it and spraying some carb cleaner in the hole the dam screw was really loose and started to close by itself when you dove the truck. I fixed that problem with teflon tape. I came to the conclusion that the tb is carboned up and needs to be taken off and cleaned good. BUT, since I am NOT Mr. goodwrench I am reluctant to do that. I was hoping to use some seafoam and run a few tanks of gas w/the additive and see if that help. I have not done that yet. I was wonder though if you took all the ducting off the tb and started the truck and then sprayed some seafoam or carb cleaner if that would work?

Co_94_PU

iTrader: (-1)

love that idle screw, been fighting with mine sort of also and need to do something about it. Some have o-rings some have rubber caps, I think ours are held on good wishes.

I wouldn't want any of that chunky carbon going into the engine particularly at high speed. If I couldn't remove it I would wedge it open put a rag behind it to catch gunk and get to scrubbing and spraying. Really it's only critical the goo is off the shaft so it rotates free, and there isn't any chunky buildup that keeps the plate from closing. If someone tried to lubricate the external mechanism that's likely the problem and it just needs a really good degreaser.

I'm not recalling you engine or year, but. The crank case ventilation system has the two hoses to the valve cover, the forward most one is the fresh air line and gets plumbed to the throttle body ahead of the plate. This fresh air line is the source of some of the build up, the rest is EGR crud, or from the pcv side.

That hose is the same size roughly as the brake lines people like to run seafoam thru.

Co_94_PU

iTrader: (-1)

Sorry guess I got distracted and didn't answer the question.

Re sea foam in the fuel.

The fuel gets injected right near the valves, on the engine side of the throttle body, it's not going to clear up any hi upstream
​

Barry D

Thanks Again.

Crap, I was hoping to just dump something in the gas and it solve my problem....guess not. OH well. My Idle screw has hard plastic and not an o ring per se. If yours has the o ring I have a o ring set from harbor freight with the correct size. I could send you info on the particular set it was like 7 bucks for several hundred o rings One last thing... the idle screw on my tb is part of the tb and you can not buy it seperate....
my rig is a stock 2dr 90 v6 3.0 5speed 4x4 sr5, I did put wheels and tires on it and a rear sliding window . 142000 miles with zero problems, excluding the fn tb issue. It has the original breaks and the rubber band was changed 1x. I am the original owner... bought it new in 1990 for 14,700.00. love that truck

mct75

I read somewhere about a coolant temp sensor going out and triggering high idle randomly. Something to check!

Barry D

Thanks

I will ck it out. If a sensor goes out does it trigger a code?? This fn serging thing has not triggered any codes.... I do not know wtf the problem is. Only thing i can think of is carbon

DallasTX

I cannot comment about the coolant sensor triggering a code, but having just pulled my engine to replace the head gasket (1992 3.0) I can tell you the coolant sensors get quite brittle with age. The whole body of the sensor fell apart when i tried to remove the housing and I had to buy a new sensor and connector housing.

Co_94_PU

iTrader: (-1)

Just rereading the thread. I bet you can turn the base idle down a little farther. The MT spec is 750. After setting the base idle take it out of diagnostic mode and kick on the AC, it should add 200rpm if it goes higher the leak is in the idle up valve or they messed with it when you had the AC work done and it need readjusted.

Barry D

Thanks for the replys

I checked out the temp sensor and here is what i found

Symptoms of a Bad Coolant Temperature Sensor

If your vehicle starts to use a lot more gasoline than usual, or black smoke is starting to come from the exhaust pipe, these are indicators that the coolant temperature sensor in your vehicle could be defective, and needs to be replaced. If you start having trouble starting your vehicle after it has reached its normal operating temperature, this is usually a very good sign that you need to have the coolant temperature sensor checked. To confirm, you could run your vehicle through an emissions test. If everything else is in order, failure in this test should be because of a faulty coolant temperature sensor.Another telltale sign of your coolant temperature sensor not functioning properly is if your engine is overheating frequently. This can possibly happen when the coolant is leaking, causing the temperature sensor to behave erratically. In many vehicles, a faulty coolant temperature system will trigger a check engine light or service engine light on your car

My truck has none of the symtoms noted above.

I will look into the idle up issue and perhaps it may have some bearing on things. I will get back to you on that one

Barry D

The wonders of the internet

Three Methods:Identifying Issues with an Idle Control Valve
Checking to see if the Idle Control Valve is Functioning

Method 1 Look for a high engine idle. A common symptom of a faulty idle control valve can be a high idle. Start the engine and look at the tachometer on the dashboard. Most vehicle’s engines will idle at our below one thousand RPMs. If you are familiar with your engine’s normal idle, compare that to its current RPMs.[1]

• If the vehicle’s engine is idling well above 1,000 RPMs, it’s probably too high. OK, I have this one
• Vacuum leaks can also cause a high idle. Checked for leaks did not find any