Idle Issue (1 Viewer)

[LFD2037]

I have an unusual idle issue. It's been an issue for 50K miles but has steadily gotten worse. Idles fine when in gear or AC idles up the engine a bit. Problem is in park it misses pretty bad, but only in park at idle. What would cause it to miss at idle in park/neutral but not miss at all when in gear or idled up when in park (775rpm+)? Thanks.

 

[Mighty690]

Any leak in the intake system, including the MAF, can mess with you like this.

 

[LFD2037]

I've searched visually and used starting fluid. Neither showed any leaks.

 

[Timpanogos Slim]

Possibly the idle air control solenoid - which isn't a solenoid at all but actually a stepper actuated plunger. Might need cleaning.

The FSM says to remove the throttle body from the intake manifold before removing the IAC and that will look like BS to you until you strip out the head of the bottom phillips screw. The angle is all wrong. The good news is that you don't really need to replace the tb gasket since it's a steel gasket between two milled faces. Even if it's damaged you can just coat it with spray-a-gasket silicone. Replace the phillips screws with socket head cap screws and you won't have to remove the tb again for this job.

The test procedure for the IAC in the FSM is sorta bull****. The four wires are not four different settings. Like i said - it's a stepper. A multi-coil motor that moves in steps. Really testing it requires a stepper controller - an electronic device that sends the right series of pulses to move the plunger in and out. one of these days I'll slap together an arduino sketch to test the IAC valve. Not that this will help most people.

Other than that, vacuum lines. 95-97 have about 7 feet of vacuum line vs. the 10 feet or so on a 93-94. A lot of it is tucked inside the bend of the intake manifold. It's super fun.