'94 Chevy 5.7L idle way too low...


prginocx
04-03-2005, 11:17 AM
This truck is a 4X4, AT 4spd, 5.7L V8 with TBI. About 100k miles. Haven't owned it very long and I did do the tune up when I bought it (Plugs, Air filter, Tranny fluid/filter, Oil & filter, New Batt, Flush coolant) I did spray some TBI (NAPA) cleaner stuff into the intake, and it did clean off some of the varnish.
Cold start idle is up and warms up truck fine. After engine is fully warmed up when you stop at a light the idle goes way down, almost dies. around 2-300 rpm by the tach.
When you are waiting at a light if you shift into Park/Neutral, the idle goes back up to about 600rpm runs fine. Shifting into Reverse/D, 2 or 1 idle goes down the same way, almost dies.

When you let off the brake to start moving, difficult to rev up smoothly, chugs a little before it will start revving up....

What tells the computer to compensate for the tranny load while waiting at a light ?

jveik
04-03-2005, 11:38 AM
umm, well i have the same problem with my 73 cheyenne 350 which as you know is the 5.7 liter. if its cold outside it runs like a top on the fast idle but when i get that fast idle cam shut off on the carburetor it sputters a lot and dies in gear. it also will sputter and backfire at a stopsign when i go to start moving again. after its completely warmed up it runs like a top again. for my instance i think its my choke on the carburetor turning off too soon or something like that. since you have TBI i dunno what exactly that entails since it obviously doesnt have a choke. but maybe some sensor that enriches the fuel mixture when the block is still cold is not working right or something is wrong with ur tbi unit. thats the only thing i can see. could maybe ignition timing have something to do with it, or is it also completely computer controlled and unchangeable?

bigdaddy1832
04-03-2005, 03:09 PM
For the TBI it uses a ECT (engine coolant temperature) sensor and a TPS (throttle position sensor). Other things that may cause idle problems are EGR valve not working right, vacum leak,air filter clogged are just some of the things you should check.

J-Ri
04-03-2005, 10:58 PM
If you have access to a scantool, check to see what the computer is seeing for the engine temp. When the computer is in open loop, it doesn't use the ECT sensor as an input.

If you don't have access to a scan tool, I'd just replace the ECT sensor. That is most likely the problem.

amac209
04-03-2005, 11:43 PM
i would look at the idle air control motor. sometimes the passages get plugged up with carbon or the motor gets stuck.

antonio demarco
02-13-2007, 10:44 PM
what was the out come. what did u end up doing

abaird
02-13-2007, 11:17 PM
Not to be nitpicky or rude, but in open loop the ECT is a very important input for fuel delivery. The O2 sensors are ignored in open loop.

edbrycem
02-15-2007, 12:34 PM
I can't think of what its called, but the vaccuum from the throttlebody to the pcv might be plugged, I had it 2x's on 2 diff. trucks. It tends to plug up in the t.b. where the hose goes on, lacking ventilation from the crankcase. It takes a second to check and a moment to clean out if it is. When mine was plugged I just used a drill bit to clean it out. (I held the bit and pushed it in and out, not in a drill). It fit perfect in the little port and it worked, If someone walked in while reading this outloud, it really wouldn't sound good.LOL

Scrapper
02-15-2007, 12:58 PM
iac or tps...anyway sounds like to me..

dhicksaw
01-24-2009, 06:21 AM
This truck is a 4X4, AT 4spd, 5.7L V8 with TBI. About 100k miles. Haven't owned it very long and I did do the tune up when I bought it (Plugs, Air filter, Tranny fluid/filter, Oil & filter, New Batt, Flush coolant) I did spray some TBI (NAPA) cleaner stuff into the intake, and it did clean off some of the varnish.
Cold start idle is up and warms up truck fine. After engine is fully warmed up when you stop at a light the idle goes way down, almost dies. around 2-300 rpm by the tach.
When you are waiting at a light if you shift into Park/Neutral, the idle goes back up to about 600rpm runs fine. Shifting into Reverse/D, 2 or 1 idle goes down the same way, almost dies.

When you let off the brake to start moving, difficult to rev up smoothly, chugs a little before it will start revving up....

What tells the computer to compensate for the tranny load while waiting at a light ?
I have the same problem I put a new ect,tps,pcv valve and I still have a low idle so low in any gear besides p or n that if i press the brake and turn the wheel it will die.

david crouch
03-03-2009, 06:57 PM
I have the same idle issues with my 1994 Blazer while its under a load.:banghead:
IAC, TPS, PCV, EGR, ECT replaced.
If I have any luck I will post it.
If anyone can help; please do so, really like the truck.

David

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