stumbling under load
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Fleet Mechanic
Joined: Aug 2002
Posts: 1,568
Likes: 33
From: Swansea SC
stumbling under load
Just replaced my IAC valve and throttle position sensor which helped the stumbling , now i am getting a high idle after the 2 min warm up idle . ideling around 1100 rpms . After changing the iac and tps , truck runs great, took it for a 10 miles drive all ok, when in gear idle normal, in neutral or park near 1100 rpm . Any suggestions???????? TR
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Did you clear codes from the ECM? (Disconnect the battery for about 10 minutes). With all that replaced, clearing the codes and taking the truck for about a 30-minute drive (Highways and surface streets) will allow the ECM to "relearn" parameters with the new components in place.
If that doesn't take the curb idle down under 1000 rpm, check for vacuum leaks.
If that doesn't take the curb idle down under 1000 rpm, check for vacuum leaks.
Thread Starter
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Fleet Mechanic
Joined: Aug 2002
Posts: 1,568
Likes: 33
From: Swansea SC
yes cleared codes , 33 , 31 and took for a 10 miles drive --stumbling is gone --strong smoothe take off even at 55 when pressing accelarator. Just must have to relear the idle will try (time permitting) THANKS Grey. TR -------Tried cleaning iac to no avail so i replaced iac and tps 
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
Actually its good that you replaced the IAC. Code 13 is indicative of either a poor connection or bad IAC. And Code 111 is the "All Clear"... clean bill of health for the EEC-IV system so you should be good to go.
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Fleet Mechanic
Joined: Aug 2002
Posts: 1,568
Likes: 33
From: Swansea SC
Yes Grey, i tried cleaning it, wrapped up soleniod etc abd same results , i had the original that was cleaned previously , same results after a drive so the new iac and tps fixed that problem .After a long drive yesterday it still seems to idle high 1000rpm sometimes 1200 .So now its time to find the vacuum leak. I tried unhooking the iac and idles same.Under previous posts (research)it said no change , vacuum leak---just a pita trying to find it ,truck has most original vacuum hoses-hard plastic and suggestions to what to spray or tips n trick are appreciated thanks TR For a while truck has leaked a combo oil and nanti freeze from the bell housing??? this indication is a leakywhat?now it just drips a small amount of oil
Lead Driver
Joined: Sep 2002
Posts: 9,182
Likes: 12
From: Gateway to the West
You say the idle remains unchanged even when disconnecting the brand new IAC?
Is there any chance the throttle plate stop screw has been messed with?
If not, then you are on the right track hunting down vacuum leaks.
Is there any chance the throttle plate stop screw has been messed with?
If not, then you are on the right track hunting down vacuum leaks.
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Fleet Mechanic
Joined: Aug 2002
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From: Swansea SC
No, the throttle body set screw has not been changed. i installed a 56mm bbk tb back in 04 .What do i spray to check for vacuum leaks some say carb cleaner ?
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From: Longview, TX
I would suggest about 25 feet of rubber vacuum hose. Some of the plastic lines on mine were in a split plastic harness near the firewall and difficult to test by spraying. Take a picture of the vacuum sticker under the hood and mark everything...hoses and print of sticker. If the plastic hoses are not leaking yet they are going to so just go ahead and replace them.
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Fleet Mechanic
Joined: Aug 2002
Posts: 1,568
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From: Swansea SC
Kem it was new back in 2004, i also have a edelbrock upper n lower and it is hard to check the plastic lines around the upper mani. I have tried all the lines(carb spray) upper n lower manifold---- temp fix i back off the screw one turn(counted the screw thread to return when i find the leak (if i do). Idle (cranking) 1400 two mins approx, then 1000-1100. Backing the screw idles 1250 two mins then 850-900rpms. Thanks TR
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I'm going to be like a broken record with this for the next few days, but change your MLPS if you haven't. My idle started getting really weird, 1200RPMs until I tapped the gas, then down to 900 or so, reved high in between shifts, etc. I thought it was normal (like the kickdown and on an old carbed vehicle). Changed my MLPS and now I get a 550 idle in park, 550 idle in drive (no high rev in between shifts). It revs high on first start, then drops almost immediately to 550 without having to tap my gas.