I have a 1990 4-Runner that I changed the spark plugs, spark plug wires, distibutor cap, and rotor. Can someone tell me how to adjust the idle speed on the motor?? I can't find an idling screw!! Right now it idles between 300 to 500 RPM-idles rough.

It must have a problem. The idle speed is set by the computer. Check the codes by jumping terminals Te1 to E1 with a paper clip, etc. The check engine light will flash codes. If you have a repair manual it will tell you what they mean.

See:
http://www.troublecodes.net/Toyota/

Hey can someone out there help me find where I need the stick the paper clip to jump TE1 and E1 so I can find out what the problem is?? I took the lower plastic dash piece off. I'm looking for the TDCL. Is it by the fuse box??

I am receiving a code 12 for knock control sensor signal and code 51 for switch signal. Can someone tell me where the parts are on this truck so I can either go buy them a dealer or find at junk yard! Need immediate help

You are looking at OBDII codes. Your truck is OBDI compliant. Sorry, my link above is for OBDII codes. My mistake.

I read Code 12 as "No rpm signal to ECM"

This is Crankshaft Position Sensor or distributor or their respective electrical circuits.

I read code 51 as No Throttle Position Sensor signal, gear selector signal or A/C signal to ECM.

This could be A/C switch or circuit, A/C amplifier, Neutral/start switch, or Throttle Position Sensor or circuits.

Code 12 has been fixed, but I am still struggling with Code 51. When the car is idling, the RPM goes between 300 to 500 RPM. Is the Throttle Plate sensor the problem?? If so, where is it located?? How do you also test the A/C amplifier as well?? Thanks, need help! Darn 4-runner dies with I am at a signal light waiting for it to change.

The throttle position sensor is located on the throttle body at the end of the throttle shaft and has a four-conductor connector attached to it.

Top to bottom with the sensor to the left of the connector, the terminals are designated:

VC
VTA
IDL
E2

The resistance between these terminals is dependent on the throttle position. A feeler gauge is placed between the lever and the stop screw (external to the sensor) and the following resistances should be found:

Clearance Terminals Resistance
0 mm VTA - E2 0.47 - 6.1 kOhms
0.50 mm IDL - E2 2.3 kOhms or less
0.77 mm IDL - E2 Infinity
Throttle full open VTA - E2 3.1 - 12.1 kOhms
Always VC - E2 3.9 - 9.0 kOhms
==============================
If you have a 3-conductor TPS, with the TPS to the right of the connector, the pins are designated:

E2
VC
VTA

the resistances are:
Fully Closed throttle valve VTA - E2 0.2 - 5.7 kOhms
Fully Open throttle valve VTA - E2 2.0 - 10.2 kOhms
Always VC - E2 2.5 - 5.9 kOhms

If out of spec, replace the TPS.

The only information I can find on the A/C amplifier is that if everything else works fine, try replacing it. I can't find any test for that unit.

Would this cause the idle to fluctuate?? Also, where is the A/C amplifier located and what is the TPS?? Hate to act stupid, but this is my first time working on the vehicle!! Please advise and are their any pictures of these items????

A/C Amplifier is behind the dash where all the A/C stuff is (sort of a box). I think it is only a circuit board. I don't see how this could affect your idle speed. That's why I didn't put much effort into figuring out anything about it.

The TPS tells the ECM what you are doing with the gas pedal and adjusts the fuel delivery. This is most likely your problem. Get a digital multimeter somewhere and check the resistances in the previous post. Alternatively, check the price and just buy one if it is cheap enough.

Results from test. VTA - E2 zero. IDL - E2 needle did not move on Ohm meter at 0.50 mm. Same results for IDL - E2 at 0.77 mm. I assume TPS is DOA and affecting idle speed??

If my specs are correct, and I understand what your meter is telling you, then that is true. My specs were from a generic 3.0L TPS unit. I am assuming your TPS unit is the same. Make sure your terminal assignments are correct. That is the obvious way to screw this up.
When you say the needle didn't move, is that high resistance or low resistance?

You had the 4-terminal TPS sensor?

I think it is a pretty safe bet, but there are no sure things...

Brian, fantastic diagnosis!! The TPS was defective so when I checked when I did the OBD test, everything checked out O.K. The check engine light flashed on and off every 1/2 seconds. I HAVE ONE ONLY QUESTION....WHAT MIGHT CAUSE THE ENGINE TO JUST BARELY HESITATE AFTER I AM AT A STOP LIGHT AND STEP ON THE GAS??? PLEASE ADVISE!!

Your engine isn't going to run the way it did when it was new. The valve clearances have changed, the cams lobes are worn so you don't get as much valve lift as you used to etc. You can try cleaning your injectors with a can of Chevron Techron addditive in your gas tank. You can also clean your throttle body. See:

http://www.4x4wire.com/toyota/maintenance/30_V6/throttle_body/

This damn Toyota 4-Runner is still giving me fits!! When the vehicle is idling and I step on the gas it's still missing. When I step on the brakes and step on the gas pedal, the vehicle misses and when I step on the gas full throttle, the CHECK engine light omes on. When I turn off the vehicle and start the engine, the CHECK engine light goes out. It feels like the vehicle is running on only 3 or 4 cylinder!! Can someone please help advise with some other advise??

Check for new codes