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Discussion Starter · #1 ·
Hi, i have a 1993 chevy s10 2.8. I just replaced the factory Tbi unit with a Holley 400cfm(2.8) unit and I noticed my rpms take longer to come down to 1000 after going up to 2000+ rpms. Does anyone know if this is normal or what I can do to fix it. Also my rpms go between 1000 to 800 up and down. I checked all my vacum lines and everything seemed to be ok. Could it be my fuel filter that is clogged? Thanks
 

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i think it's normal for an engine to have idle speed 'wave', though i'm not sure if it should be that much
 

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Discussion Starter · #3 · (Edited)
I changed the pcv valve, and the fuel filter and the problem still persists. I noticed that there is a heavy smell of gasoline coming out from the exhaust and around the engine bay. Could I be running rich? I tried adjusting the carb but it still dosnt improve. If I adjust the idle high it jumps from 800-1100rpms, and if I adjust it from low it jumps from 600-700rpms and back. In the morning when I start the truck it goes to 1100rpms. When I am driving the car on the street, when I change gears, the rpms dont seem to come down fast enough they kind of stay up there. I bought the carb off a guy that had it sitting in a box for 3 years. The guy I bought it off said that the original guy that bought it only put 500 miles on it. What could be my problem? Any suggestions are greatly appreciated.
 

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The Holley TBI is advertised as being for the '85 1/2 to '89 model years. The difference being the different TPS (IIRC). The connector is supposed to be different, is that connected correctly? I don't recall off hand if the voltage range is the same between the two TPSs, this could also cause problems.

Did you do the proper procedure for seating the idle solenoid, before setting the base idle? Did you thoroughly warm the engine before setting the base idle speed? Even mine varies quite a bit till the coolant temperature reaches approximately 200*, then it settles down to about 700-800 rpm (where I've adjusted my base idle speed to).

If the engine was thoroughly warmed up when you set the idle speed, then the other thing that could be bad is the idle control solenoid.
 

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Discussion Starter · #5 ·
Yes, I changed the tps plug in from my 1993 and bought a 1989 one so that it would plug right in. While adjusting the screw for the idle, im pretty sure it was warmed up because it was running for about 5 minutes. My rpms jump around from 800-1000 some times and it sounds like I have a cam or something. I tried adjusting the fuel regulator and it helped a, little turning it down. Right now the truck when it seems warmed up it stays at 1000rpm when idleing. When I tried adjusting it last time it would go from 800-700 and then drop below 700 and go back up to 1000. Im not sure if im running rich or something. The truck seems to jump sometimes while leaving a green light but when its going it dosnt sputter. When I change gears the rpms seem to stay up and im not sure if thats normal. They drop but slowly and sometimes they drop fast like my old carb.
 

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i saw what you did there!
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the IAC controls this idle return rate

it returns to idle at a rate determined by signal from the ECM

maybe it is sticking

or not set properly initially

it is supposed to b set a certain length initially or the ECM cant control it properly

if it still wont work right then its either faulty or the ECm cannot control that style IAC

you cna unplug it and run without it then the throttlw will return immediately like a carb engine

i return mine with it disconnected sometimes like when i am hauling a heavy load, so it will slow up quick

like i will be in the morning first thing
 
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