I have a fast idle when my 1990 AW4 with 256,XXX warms up. I've been reading most of the posts of fast idles and have cleaned the IAC (looks to have been replaced before) and throttle body after my tune up. I didn't remove the throttle body just sprayed inside it. Tune up consisted of cap, rotor, wires, plugs, and fuel filter. I have also checked the voltage of the TPS. It was at 4.67v input so I adjusted output to 3.88V. Checked all the vacum lines i could see and seem to be alright. When I pull the vacum line off the map sensor when it is at high idle it comes back down. Haven't checked for vacum leaks with some throttle body cleaner yet or checked the intake manifold bolts, but wanted to get some ideas on the map sensor first. It would be hard to hear If I have a audible vaccum leak because the power steering pump starts whinning when it gets warm as well!

I was getting crappy gas mileage as well, around 12.4mpg on 85 octane. Ran 87 in it this week and it seems to like it better im at 90 miles at just a smidge under 3/4's.

So could it be map sensor or should I keep looking elsewere for vaccum leaks, or egr valve, and replace the o2? The jeep passed emissions a couple of months ago with flying colors?

 

skud I'd like to more know about that map sensor as well, I hope someone can educate us!

 

For sure! I haven't checked the voltage on it yet but I would think that the idle would run higher after pulling the vaccum line to it. Instead it goes from the high idle to what seems like a normal idle to me. Don't have a tach on it.

 

i would put a vacuum guage on the intake and see what the vacuum is,should be about 15",when I unplug my map the engine wants to die,you may have a vacuum leak but not able to here it.

 

Testing your MAP sensor is easy enough - here is a link to a nice page with all the RENIX sensor diagnostics on it.

 

Well I finally got around to figuring out my fast idle prob. It was a combination of the Idle stepper motor and a intake vacuum leak. I started by plugging the IAC hole with my gloved hand and sure enough it wanted to die. Put it an IAC from the jy and with the same procedure it stayed running. Idle was still a tad high when warm and only after it was warmed up. So sprayed a little tb cleaner around the intake and right up front the idle came down when sprayed. Sure enough that front intake bolt was a lot looser than the rest. Tightened her down and seems to be idling normal now. Thanks to a little research and reading through the posts I fixed it without having to throw a bunch of expensive electrical components like map sensor, coolant temp sender and the such. I guess Ill know better tomorrow when I drive it but I know its gonna be good just by the way it was idling.

 

Re faster thanthemhow much faster can it really be?

 

Re faster thanthemhow much faster can it really be?

 

Re faster thanthemhow much faster can it really be?

 

Re faster thanthemhow much faster can it really be?