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my girlfriend's 87 5.0 idles crappy. when it starts up it idles normal around 1,000ish but every few seconds it'll drop down to around 500 rpm. it'll keep doing this mostly when its cold but can do it after its been running awhile too. also, if you shift it into gear, when it hits the low point of the idle, it dies.

I've read up on it and see probably vacuum trouble, MAP, MAF, EGR or something of that nature. the car however, is in texas and i'm not but will be there for the weekend shortly so i won't have long to look at it...just wandering if anyone knew of a good step-by-step fault isolation procedure to take that would help to narrow down whats wrong.

Also, does autozone have a vaccuum tester or not? I appreciate your responses. Oh yeah, also, its a convertible and the driverside window squeals loudly when you put it up and sits at an angle going up or down unless you manually shift the window position--power windows too. Thanks.
 

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I ussually find vaccuum leaks by spraying throttle body cleaner around the engine compartment while the engine is running. If you hit the vac leak with the cleaner the idle will change. I found many leaks this way. Also clean out the throttle bypass valve, they get dirty and cause a wacky idle. Check the distributor cap terminals,wires etc. Purchase code scanner they are cheap, you can diagnose electronic componet failures. Good luck!
 

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It might just need a tuneup. Wouldn't hurt to pull off the battery cables and clean the connections, too. I think the 'zone sells a cheap vacuum tester, but you can just inspect the lines - especially the emissions stuff behind the pass. side shock tower. Also, see if you can get ahold of a gauge, and check that fuel pressure, you want 39-40 lbs. idleing with the vacuum line off of the regulator.
The window needs two new "window guide bushings" - the ones which ride up and down the post inside the door. I got mine from: www.50resto.com
 
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