idle issues

[Exporunner]

I have a 94 expo automatic. When I start the truck up the rpms are around 1200 then fall down to 750ish like its suppose to. When I rev the truck up it takes a while for the rpms to drop. So if I rev up to 3 grand it slowly falls to about 1200 then holds there for about 5 seconds then slowly drops to 750 again. Almost like a vacuum leak but all the lines are good. What could be causing this? Any help would be appreciated.

 

[wood1]

You could try cleaning the IAC valve on the side of the throttle body. Q tips and some rubber safe solvent... it's easy to do and free.

 

[Exporunner]

Okay I'll try that. I've cleaned the maf the trottle body and checked all vacuum lines and ran sea foam through it .

 

[wood1]

Let me know how it works out

 

[Exporunner]

The iac is that cylinder thing on the drivers of the tb right?

 

[mikewild]

yes

 

[wood1]

X2, sorry was out for a while. Two bolts, it has two holes, gasket is reusable.

 

[Exporunner]

X2, sorry was out for a while. Two bolts, it has two holes, gasket is reusable.

okay I'll try that after work today. Worked 14 hours yesterday and was in no mood to do anything

 

[jd4242]

if that dont work check the fuel pressure regulator line for gas in it and lower manifold bolts

 

[nexis]

sounds like a IAC, cracked hose, or bad intake gasket set. cracked hose can be a real PITA to find, one trick ive found works amazing, is grab a propane torch, turn the gas on low, but dont light it. move it over and around your hoses with the motor running. if/when you find the leak, the engine will sound different, and may rev up some.

 

[Delta_1980]

I had some problems with my idle, turned out to be the vacuum hose going to the charcoal canister. The rubber 90 failed. and was drawing air.

 

[Delta_1980]

I had some problems with my idle, turned out to be the vacuum hose going to the charcoal canister. The rubber 90 failed. and was drawing air. it had tiny pin holes in it.

I don't know how I posted this twice, oops.

 

[Exporunner]

Okay I'll check that. I remounted the charcoal canister on the core support and had to add a longer hose after the 90 degree so ill make sure it's all tight and not leaking.

 

[Exporunner]

cleaned out the iac, it wasn't very dirty and the idle hasn't changed. But when I just unplug the iac the idle is normal. On top for this when I'm driving and hard in the throttle the truck will hit a rev limiter around 3800 and won't shift unless I come off the throttle. I replaced the crank shaft position sensor because that's what fixed my s10 from the same problems but no difference. Anyone every experience anything like this?

 

[raiper]

sounds like the problem i had with my truck. Idle would bounce and engine would run crappy and had power issues. When i d/c the IAC it ran perfectly fine, well better than it did with the IAC connected. Replaced IAC after multiple cleanings failed and well its fixed now. so if u got a buddy with another x that runs fine, plop his IAC on urs to make sure its the problem, but my money is on IAC

 

[Exporunner]

I got a friend who works at O'Reilly so I can just try parts and if they don't work I just return them. I'll try getting a new iac today. Did you truck not rev all the way up in all the gears? I haven't tried driving it with the iac unplugged yet.

 

[raiper]

ya im gonna say it did kill the revs and powerband in all gears. i still vote to just swap it out and see. my idle was weird like yours and my exhaust smelt a lil funny as well. cleared right up after i switched

 

[Exporunner]

Cool I got an iac and I will throw it in tomorrow and let you all know. I need to get this this ready for the short course track tomorrow.

 

[Exporunner]

Iac didn't work. Could the ecu be fried somehow for these two things to be happening?

 

[jd4242]

Yep.