need help fixing idle speed

[lawdoc]

I have a '88 5.0 HO Lx. It has developed a high idle, right at around 12-1300. but if i leave it idle for a while, at a stop light for instance 5-10 minutes the idle will fall and level at around 7-1000. What can cause this. I've checked my timing it is on the line and my vacuum is also steady and in range. The only thing i can think of is that maybe the spout chip is bad but i don't know how to check it. Also the maybe the tps but i cant remember how to check that either please help.

 

[tannerc91gt]

Clean the idle air control motor. 1000 is way high for idling they like the 650-800 range.
Push comes to shove, adjust the idle set screw to lower the idle

 

[HISSIN50]

Pull codes and look for a vac line that has cracked or come off. A small leak won't drop your manifold vac reading much but can affect the idle.

 

[njoliver]

Clean the idle air control motor. 1000 is way high for idling they like the 650-800 range.
Push comes to shove, adjust the idle set screw to lower the idle

if it was idling normal before you should not touch idle screw as this might just be covering up a problem. you should never have to adjust idle screw, unless you have adjusted it in the pass. clean and check IAC,

 

[Mopar1]

Pull codes and look for a vac line that has cracked or come off. A small leak won't drop your manifold vac reading much but can affect the idle.

Ditto. Mine would idle at 700 then shoot to 1200 or so after a few minutes, then back down to 700. Drove me nuts. Discover a split vac line in the upper intake. I couldnt even see it. I think it was starter fluid I used to find it. Frustrating as hell.

 

[Mustang5L5]

Pull the codes