Some background info.
93 Toyo with 329Km.
Lasty summer before parking for winter i replaced Rad, coolant hoses and thermostat, distributor cap/rotor, plugs and wires and AFM sensor. In the fall the idle started surging 1500-1700rpm roughly. so i parked it for the winter.

I started working on it again with the warming weather.
I replaced the throttle body with a wrecker pulled unit. cleaned and replaced TB gasket. Coolant lines were not plugged but as i read on the forum that doesn't necessarily mean anything.
It starts cold very well. Idles at 1800-2000rpm with idle screw all the way in. after it runs for abit the idle drops to 1500rpm. (sometimes after its been ran and parked if you start it up it idles at 1000rpm but surges shortly after driving) Shortly after that the idle rpms start surging and when driving you can leave it in 2nd gear and it will just keep driving without your foot on the gas!! kinda scary in parking lots ;-)
with the new throttle body its seems alittle more responsive.

IDEAS:
I am going to test/measure the Cold start injector in the next few days.
Ive read that idle surges can be caused by a water pump/ timing belt issue aswell. (its on the list of things to do)
By installing a used throttle body and experiencing the same thing i dont think its the TPS sensor. My gas mileage also dropped off when this problems started last fall.
I discovered an exhaust leak between headers and pipe on the drivers side. the gasket is gone. could this lead to misinformation at the ECU/02 sensor?

i appreciate any feedback guys

 

Sounds like the iacv in the throttle body is stuck open. Are you sure the coolant lines aren't plugged? If the idle screw is all the way in, the motor should idle very low , if at all.... To test my theory, remove the intake hose and put a piece of electrical tape over the air bypass hole inside the throttle body. Be sure to clean it so tape will stick. Start the engine and u might need to back out the idle screw a few turns. If it no longer surges and has a problem with cold starts now you've found the problem. Keep us updated.

 

IACV ? what does that stand for

Interesting test with the tape over the bypass! i did that with the original throttle body in the fall after reading this forum. It didnt idle surge anymore but the truck ran really rich and had no power.if i recall correctly it did hesitate to start when starting cold. I have not tried it with the replacement throttle body yet.

" If it no longer surges and has a problem with cold starts now you've found the problem. Keep us updated."
The problem would be the throttle body coolant temp switch or cold start?

 

I ran air and cold water through the coolant lines on the replacement throttle body.

 

Iacv= idle air control valve

 

Is the coolant system full with no air in it? Are the lines plugged that come out of the motor going to the iacv?

 

Idle Air Control Valve, that is the sensor integrated with the coolant lines and the air bypass hole in the TB right? (the part that is no longer made and the reason i change the throttle body in the first place arghh)

Im not sure of the IACV coolant flow direction but I pulled the front one off. Brass barb fitting and the coolant was looking pretty dark in there considering i redid the cooling system last year (except the water pump). I took some wire and cleaned the pipe out. I turned the engine on and coolant started sputtering out the top. I didnt check the rear one. There is a cover plate for that sensor and was very tempted to remove the plate on my original TB to just investigate. My original TB was really gunked up.

THNX YotaWorx for the help!~ i really appreciate it.

 

Any update?

 

checked cold start injector. 3.6ohms: so its in spec. i sprayed carb cleaner and found no vacuum leaks.
I dont think there is any air in the coolant lines, i burped it when i installed the rad and hoses last year.
I noticed when im driving the truck and i pop it into neutral before coasting to a stop. the RPMs stay constant around 2k but if i hit the gas it will drop to 1200. sometimes when the idle is surging and i hit the gas it will sometimes stay high until i hit the gas again and the rpms will go down but then start surging again.

i guess i will have to pull off the coolant lines from behind the throttle body near the firewall to see if its clogged.

 

Did you adjust your TPS?

 

i did not adjust tps. goona do that this weekend and pull the rear TB coolant line off at the manifold. to check if its plugged.

 

Adjust your tps first.

 

Ok TPS is adjusted. used this link : http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
I checked the rear coolant line and it didnt appear to be blocked.
It idles alittle lower (cold start at 1800 and drops to 1500 when warmed. I adjusted the idle scew so its 1.5turns out from screwed all way in and it drives really nice. A slight improvement on throttle response. BUT, It stills does the hunting/surging when warmed. Dashpot? Try a different TB?

 

So the idle switch in the TPS is CLOSED with .020" in the stop, and OPEN with .030" in the stop?

 

yup, getting a low ohm reading when closed switch 0.5mm 0.02" and open circuit with 0.77mm 0.03"

 

Umm, closed switch @ .020, open circuit @ .030, this what you have?
If yes, block off the idle air port inside the throttle and see if the idle is stable.

 

blocking off bypass reduces my idle and no more idle surges. With the idle screw 1/2" turn out from all the way in my idle is just under 1K.
so i guess time to try another throttle body