Surging idle 1999 yukon slt 5.7 having idle surges, high and low. i've relaced the IAC, cleaned the throttle body, replaced plugs and wires, the main engine computer was replaced 7 months ago but at crank idle drops then surges over 1000rpm then drops to normal. Is also surging up at times while driving. Help

No, remove and clean or replace the IAC valve...use trottle body cleaner or brake cleaner..IAC means Idle Air Control...cheers

There are two coolant lines that connect to this Honda IAC to help quiet the operation of the valve. The part number for a OBDI 1992-1995 Honda Civic Idle Air Controller is 36450-P28-A01. While the OBDII version of this valve is 36450-P2J-J01, and the two units are very similar in design and execution. The EACV or Electronic Air Control Valve is a big part of maintaining your Honda Civic idle. If you've checked your IAC and your Honda still suffers from a surging idle, check your FITV. This Honda Idle Air Controller or IAC is under the throttle body and incorporates into the throttle body passages o locate your Fast Idle Thermo Valve, remove the intake snorkel and locate the FITV beneath your throttle body opening. If your SOHC engine is still having problems, check our guides above on how to check your FITV as well as your IAC. To check this operation, remove your air intake pipe and use your fingers to plug the passages in the lower left hand corner of your throttle body opening. If your idle surge does not go away, unplug your Idle Air Control valve and if that stops your idle surge, your IACV must be replaced. Follow our instructions on how to replace your Honda Civic Idle Air Control Valve. Need to raise your Honda Civic idle or having problems maintaining idle? You can adjust the base idle by unscrewing or screwing in the Idle screw on your throttle body. This screw allows air to bleed into the passages on the backside of your throttle body, as shown above. To learn how to adjust Honda Civic idle speed, you will not need to remove anything. With a standard screwdriver, simply locate your throttle body and Idle screw.

Unfortunately many car manufacturers don't like it when people do it themselves, so they have a little b**by-trap they like to spring on you. If you replace the TPS, IAC, etc, the idle will many times no go back to normal and you will need to have the computer "relearn" so it can rest it back to normal! No real reason for them to design it this way, except of course to force you to go to the dealer to get it fixed! Nice little surprise they like to give their customers!

Did you change fuel and air filter,put fuel cleaner good one.

IAC sensor.

Have u checked the cadeletic converter. It can do funny things

There is a large vac line coming straight down from the throttle body that goes to the PCV system. See if it has a hole in it. It is likely sucking air.

Replace the Intake Air Temperature Sensor.
Depending on your size Engine (2.4L, 3.0L or 3.3L) It should be located where the Air Filter is. When you take the cover off, it wil be mounted into the cover. It has the only wires going to the cover.
This sends information to the Computer which adjust the air/fuel mixture - causing surges.
The 2nd recommednation: to remove, clean and check is the Idle Air Control (IAC) Valve and replace if necessary.

Let me know if this helped....

most likely idle air control sensor or low engine coolant I know sounds funny but IAC uses coolant to regulate idle. Idle air control valve or throttle body positioning sensor.

the throttle body used to get carboned up where the map senor passage is pull the vacuum hose off map and check vacuum if vacuum is not present remove throttle body nad clean passage