Gen I Idle/air/vaccum system issues

[Chubbyfresh]

A few days ago after not driving my car for a week I started it up and noticed the idle was rough. RIght after start-up the engine reved up to 2500rpm and then slowly wound down to around 800, where it began to buck and die. I suspected that my MAF needed to be cleaned, so I set about that. After cleaning it with alchohol and resetting the comp. via 15 minute battery disconnect the engine ran much better (lots of carbon build up) - but still had the idle problem. I then noticed a rasping -- which I thought at the time sounded like the power steering pump was running dry - I checked this - but it was full - I concluded that the bearings were bad on the power steering pump - so I replaced it. Let me tell you that friction fitting for the pully is a terrible set up. After replacing and bleeding the system etc my power steering works wonderfully but there is still a rasp (sounds like lots of air being sucked in or blow out of something) It's coming from the drivers side of the car - seemingly around the brake booster. The idle is still rough and occasionally while driving if I take my foot off the gas the engine lags down. I suspect there is a vaccum leak or perhaps a cracked intake manifold - though I havn't spotted the leak yet - next step is to get some smoke in there and see if I can follow the trail. Any ideas about what this could be?

 

[monkeydude3]

Check your idle air control valve.... my dad's aerostar (4.0L OHV) did a similar thing and we cleaned that and it helped. One way to check for a vacuum LINE leak is to take carb cleaner and while it's running spray the crap out of it where you believe a leak could be, and anytime you get a noticable change in the rpm or smoothness as a result of the spray, that's a leak.
I have a 1994 XL 4.0L OHV that has been a PAIN IN THE ASS about idling and vacuum issues

 

[Chubbyfresh]

THanks for the help - I havn't had time to isolate the problem, but had an interesting development. After not driving the car for a few days (it's been cold as hell up here) I started it up and it still idled a little rough - but there was no noises to speak of. The air sucking noise came back after 10 minutes or so of driving though. Kind of bizzare since air doesn't freeze.

 

[410Fortune]

IAC valve as mentioned mopst likely.
This is assuming you checkd the vacuum hoses, they come loose or get brittle and crack. Make sure they are all hoooked up.

The next step would be to check for vacuum leaks around the lower intake manifold, there are many ways to do this.....usually if its leaking you will see a high idle, not low.