Another hanging rpm thread

squeak93

15 Year Member
Jun 2, 2005
2,141
323
164
Joplin, Missouri
So my dumb ass had the bright idea to polish my plenum and throttle body. They both had a TON of oil, carbon and other chit in them from 100K+ miles. So I got it all cleaned up and done, carbon removed and everything clean.... Now the chitty part.....

My rpms don't drop while under a load. The car idles fine (oddly enough with or with the iac plugged in, so I think thats my issue). I can blip the throttle while in the garage and it goes up and down just like its supposed to. Idles 750 or so. Perfect right? I thought so. But when I take it out for a spin its goes crazy. As soon as you put a load to it the rpms stay for at least 15-20 seconds. If I shift at 3500, they stay there till I either engage the next gear or wait long enough for them to come back down. But like I said, this only happnes under a load. The throttle is not sticking, no vac leaks, I replaced gaskets..... I'm lost.

I am going to try another iac tomorrow but if that doesn't fix it I am f-ed.

Anyone have anyother suggestions. I can say that I cleaned a TON of carbon build up on the tb and a chit ton of oil build up out of the plenum. That being said there is no "loose" junk to get anything stuck. The throttle blade works flawlessly, linkage is all good. No reason it should be doing this now as it worked just fine before.


I have read may threads on this and can't find a definitive answer... I read where others have made a restrictor plate (see here http://forums.stangnet.com/541046-fix-your-slow-dropping-hanging-rpms.html) but that was for 1500 or so hanging rpms, with that work it mine is haning up so high?

My only real guess is that the iac is weak and hanging open or opening too far once the blade snaps shut. Since it is only activated when the tps reads its "low" volt setting I am assuming that the load/air needs of the engine are making the iac let much more air in that is needed. Does this sound logical? :shrug:


Oh and its late and I am not proof reading this ******......
 
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Might want to get some electronics safe throttle body cleaner, or even electrical contact cleaner and spray out the IAC valve. Possible you got some gunk still in there. It's only two bolts, and the gasket is re-useable as long as it doesn't break.

Worth a shot. Cleaning mine has helped.
 
You may want to check on this?

If your iac checks out ok, you may want to check on your PCV valve. My son had a 95 Neon that had the same problem. The rpm would hang and would take a few seconds to drop back down. It turned out to be a bad PCV valve. It actually caused a vacuum leak. The crank case vacuum is what made the rpm hang. Some of that stuff you used may have gotten into the PCV valve and caused it to freeze in the open position. Just something to think about. Good luck, Tommy.
 
I checked the valve the other day, it seems to open and close then u apply suction or blow into it. Other than a nasty taste it left in my mouth it seemed to be working good. I also applied pressue/suction to all the hoses and rubber fittings along all the lines. I have put quite a few miles on the car now and the computer has been through enough drive cycles that it should of relearned how to idle now. If anything the actual idle is getting worse and slowly starting to surge. I would suspect that my culprit is the iac. I'm going to try that after work tonight and see.
 
you most likely also removed the special grease that you aren't supposed to touch on the TB butterfly, I don't know where you will find replacement stuff though
 
Well, I got the hanging idle fixed. I put a new iac on and I can actually hear this one (its used but seems to work). My idle comes down to about 1500, stays there for about 5-10 seconds then only goes to 1k. My t/b screw is backed off all the way and it still is that high. With the iac unplugged the car barely idles but jumps to 1k with it pluged in. I do now have a restrictor on the iac lines, a 1/2 threaded brass pipe cap with a 9/32 or so hole drilled in it. I think I'll try another plug with a smaller hole to try to limit the amount of air the iac sucks in.

That being said, at least I can drive the car now.. :D