I want to replace my spark plugs and adjust the engine timing, but the first step in my manual says to ensure that the idle speed is correct, and I can't seem to figure out how to adjust that. Correct idle speed is 700rpm, and the tach on my dashboard generally reads around 1,000. Sometimes the engine jumps a bit and it drops down to the proper speed for a while, but doesn't stay there (something I'm hoping will be fixed after spark plugs and re-timing).

There's a troubleshooting section that acts as sort of an index to the manual that says information about incorrect idling is in Chapter 1. Unfortunately, I've combed through that chapter twice now and didn't find a single section about adjusting the idle! Not sure if I'm just missing it or if that's a clerical error in the manual, but figured I'd post here to save some time and frustration.

Thanks!

 

There no real idle adjustment on the throttle body. The engine computer reacts to RPM and coolant temp then adjusts the IAC valve to allow more or less air to bypass the throttle plate.

Might read up on the internet about cleaning the IAC valve for a model 5AFE engine model. Try cleaning the IAC valve and throttle body.

There is a screw on the throttle body that adjusts the throttle stop position, don't adjust this as it is factory set!

If you look on the throttle body there is a dashpot connected to a vacuum hose. Make sure when the engine is running that the plunger on the dashpot is retracted and the throttle pulley tab is sitting on the screw above.

Check for vacuum hose leaks at the small hose on the throttle body, PCV valve system, power brake vacuum hoses, etc. A small leak can cause a higher RPM.

There is a coolant temp sensor on the cylinder head coolant output pipe that tells the computer the temp. If this fails the engine can have cold start idle problems, stalling, etc.

 

Thanks Joey! Would trying to adjust the timing still be beneficial to do now, or should that be put off until I can look into cleaning the IAC valve and get the idle speed back to normal?

 

The timing seldom needs adjusting unless the distributor location was moved.

Suggest to start with cleaning. Use a cleaner safe for plastics as the IAC valve is plastic, don't use brake cleaner. CRC brand makes spray cleaners.

Also heck for vacuum leaks and other issues discussed.

Then change the ign parts you mentioned.

Timing is perhaps the last thing to do as there is nothing to wear out in the ign system to make the timing go off.

If this engine is a V6 the model is a 1MZFE, not 5SFE.