here's a good one. haven't been able to figure out yet. right after start-up, the idles goes crazy. goes up and down and can't seem to stabilize. otherwise it runs good, good mileage, plenty power, tune-up up to date. it will do it for a while and it idles ok after i turn the a/c on or put it in gear. after normalizing the idle, if i give it gas and let go, it will rev and instead of dropping back to 800 rpm (or whatever it supposed to be) it will drop well below the idle speed and struggle to keep running. it will do it for a sec and then run ok.
in a few ocassion, it has stalled the motor after i put it in gear. it's a 93 xl with 90k. it's been in the family for a while and we've taken care of it. never been abused. any ideas?
C.D.
update..
it also had this "chirp chirp" noise coming from the distributor. i removed the dist. cap and sprayed wd-40 and it helped calming the noise. also removed the idle air control and sprayed it with carb cleaner inside. after doing these steps, it stills idles erratically after start up, but stabilizes a lot faster and if i give it gas, it comes back to idle with no problem!! improvement, but still not fixed.
any help appreciated.
thanks

 

Sounds like a vacuum hose has become disconnected or you have a vacuum leak from split hose, etc. Could also be dirty mass air flow sensor but from your descriptions it sounds more like a vacuum line problem. Check carefully for a loose or disconnected line.

 

checked all the vacuum lines. everything lookes good. tested the van with one of those hand held code readers and it came up with code 412 "cannot control rpm during testing". after the van has been driven and warmed up, the idle gets considerably better. paid 10 bucks for another code test and it showed that the ECT and ATC, both temperature related, -40 deg.
idle when cold is terrible. after warm-up idle still not smooth.
i need to get this van fixed in a hurry!! thanks..

 

ok it's fixed. replaced the Air Idle Control and it's idling like a champ.

 

"Air Idle Control"? Can you elaborate? I assume the ATC you refer to is actually the ACT(Air Charge Temp.)sensor. Please correct me if I'm wrong.

 

> "Air Idle Control"? Can you elaborate?

Controls the idle speed. Under PCM control. Fast idle when cold, speeds up idle slightly when the A/C compressor clutch engages, when the PS pressure rises in the rack (when you're turning fast at low speed), when you shift from P to D when cold it boosts the idle a bit.

ftp://asavage.fdns.net/Aerostar/TPS_01a_a.png

ftp://asavage.fdns.net/Aerostar/89-3.0l-before-valvejob_01_a_a.jpg

Regards,
Al S.

 

Thanks for the info.Great pics,most helpful.