Click here for idle-stalling issues

[Johnnyiroc]

The IAC valve is usually the root of cold start problems, and idling problems. Either the car starts then wont idle, or it wont start without foot on the throttle. But car runs fine with foot on the gas. These are 2 classic symptoms of IAC failure. May not set a code. basically this thing controls the air with the throttle closed allowing the engine to get the right airflow to idle. Most failures are when the weather is cold. But not always. Here is what it looks like.
96+ is a 15 minute job, the 92-95 well maybe an hour if you are in-experienced. The cost is usually 50-70 bucks for the part. Lots of people find sucess with Napa for this part, but any identical one should be great.

[DuceAnAHalf]

mine took about an hour on my 97. the two screws that hold it were really tight dure to teh beginning of galvanic corrosion. I could not even use a stubby screwdriver on it. I had to use a #3 Phillips bit and a 1/4" wrench to break it loose. the two bolts are 10-24 x (i think) 1.5"

I was going to replace these with Socket head cap screws, so i could use a allen key if it ever failed again, but i never bought any. a little anti-seizr during re-installiation will make any future remaval much easier

[Johnnyiroc]

Good point, I think never seize and maybe hardened -grade 10.9 metric replacement bolts are the way to go.

[DuceAnAHalf]

Good point, I think never seize and maybe hardened -grade 10.9 metric replacement bolts are the way to go.

the bolts are standard thread. 10-24. thats a #10 screw not 10 mm

[Johnnyiroc]

Never noticed! It must be the only standard non metric thing on the damn car then.

[DuceAnAHalf]

im pretty sure it is standard thread. I found 2 screws that would work but they were too short.

anyways, check the threads before you go screwing it into the throttle body. I dont want someone to come here bitching because they ran the wrong bolt into their throttle body and stripped the threads out.

[93 Marquis]

Never forget to start with the easy things before throwing parts at the problem. Vacuum leaks, cracked EGR supply tubes, and loose air intake components will cause similar problems. A vacuum leak with drive a mass air car crazy.

The '91-'95 4.6 engines have a few more issues than the '96-up models, but the basics apply to all:

1. Prone to cracking the vacuum connectors on the PCV supply line that runs behind the heads. This will give you a miss and poor gas mileage without throwing a code. ('91-'95 specifically)

2. EGR supply tube from the passenger side exhaust manifold to the EGR valve is known to crack. This will cause pronounced cold start issues. (Rough idle, stumble, stall) It's not an easy part to see, but it can play hell with how your car runs. (Mainly '91-'95, but I have seen this on the newer '96-up cars as well)

3. Clogging EGR passages between the upper and lower intake. This will turn on the CEL and give you one or more emissions codes. Cleaning the passages will improve idle and MPG. ('91-'95 models, '96-up uses a redesigned EGR sysem.)

4. Loose or cracked intake (zip) tubes and crankcase vent tubes. (All years)

Ray