Need help! Engine bucking and jerking at certain RPMs

[PearlWhiteMR2]

Is your coolant low?

I believe this engine uses a wax pellet type IAC that opens and closes from the temperature of the flow of coolant. If coolant is low, the wax doesn't heat up and the idle stays high. If you have intermittent idle issues, it could be because the computer is sensing this and trying to compensate for it by lowering the RPM, and it can go back and forth.

Just an idea, based on a 3VZ-E at work that had a similar issue.

[jamminj]

@PearlWhiteMR2 - I dont think my coolant is low. I had my water pump replaced in February at a dealership so I'm sure they put in coolant when they replaced it.

So far, I've tried cleaning the throttle body and the ISC with some Seafoam Deep Creep. My idle has gone down a bit and I dont have the throttle sticking issue anymore. However, when I did the cleaning, I noticed under my car on the floor, that there was some blackish liquid that accumulated (looked like the carbon and oil residue liquid that was on my hand in the previous test). Is that normal? I made sure that very little dropped on the floor when I was cleaning the throttle body...

Also, I was able to find an ignition coil and igniter to see if those are the issues with the bucking..
I tried the ignition coil and it still occurs.
Gonna try the igniter tonight.

[jamminj]

Replaced the igniter. Still occurs.
So far I've changed most of the ignition system.
Igniter, ignition coil, dizzy cap, rotor, spark plug wires, spark plugs.

I've also tried seeing if there were any diagnostic codes but didn't get anything...

Gonna try testing intake air temperature and coolant temperature sensors today...
Any other things I can do?

[camshaft]

So the High RPM is no longer present ?
The car now idles at ?

I'm unclear where this was coming from?

that there was some blackish liquid that accumulated (looked like the carbon and oil residue liquid that was on my hand in the previous test

Other items can be TPS but then your bucking jerking would be at the same throttle angle.

[jamminj]

High RPM is no longer present. Currently idling at 1200 RPM which was what it was running at before these issues.

Something that I noticed on the highway, at 3500 RPM on 5th gear when the car is totally warm, I get the same bucking. But only at that RPM... Does that narrow the problem down?

[jamminj]

Just to update this thread...

It turns out my water temperature sensor leads were corroded. When we took it off, the thing snapped in two...
So I replaced the sensor and after a couple of days, the car ran perfectly.
I also took out the EGR valve and cleaned the crazy amount of carbon that was built up inside.

Now my idle is now at 900 RPM and runs really smooth.

Thanks for everyone's help!

[Saiko]

grats! That sensor breaks really easily, I've had two break on me in the past. The BCMR2 group is small but is an extremely nice crowd that helps out as if it were their own.

[dh4ever]

thats the same problem I had. but mine just cracked enough to limit the signal sending it funny messages. not enough to throw a code but enough to make it modify its settings to where there is drivability issues.