Hey I got a 1991 Camaro 5.0 TBI I just replaced the motor with the same 5.0 re-man engine. Everything has been peachey until recently, The motor wants to idle dip from 700 rpm's to 500 rpms back and forth when cold, and occasionaly when warm. It also, after driving it wants to hang at 1500rpm for at least 10-15 seconds before dropping back down to standard idling rpm at 700. It smells like it is running very rich. Everything has been replaced on the motor (egr, map, ignition, everything sensor wise) the only thing that hasnt been replaced is the TBI itself. I also am not sure if the tbi gasket has been replaced. I am running a Vacuum gauge off the tbi and it holds a steady 20cfm vacuum, but when dips it goes to 16cfm-22cfm. it isnt a drastic idle roam but if you listen you can hear it. any idea's what might be causing this problem?

 

You may want to:
(1)Check the Idle Air Control valve.
(2)Check that the throttle valve closes down to the same spot at all times.
(3)Make sure the throttle linkage is not sticking.
(4)Giggle the throttle valve shaft when the vacuum drops as the throttle valve may not be closing fully, or the IAC going strange.
By the way, I never heard of vacuum being measured in cfm, CFM is measure of volume, vacuum is measured in units of pressure, like PSI, or inches of mercury, or BAR, etc..

 

yes sorry its measured in inches. I was thinking of air conditioning units :P I spoke with my father, a long time mechanic and the one who helped install the motor, and said everything has been replaced except for the TBI unit itself, so im going to try replacing the two injectors itself. Where is the IAC located? and my throttle is very hard to depress it has a very rough initial push when accelerating, is their a throttle cable on these units, and where would i find a suitable replacement. Ive looked on rockauto.com but couldnt find a replacement part for the throttle cable.

 

The IAC valve is screwed into the side of the TBI assembly.

 

its not the injectors so dont look into getting them. at least clean out the iac, or replace it, its only about $25. pick up a manual while your at it, it will make it much easier to replace. also, wiggle the throttle shaft to see if there is any play in it. chances are the bushings are worn out causing the butterfly to hang up at different spots. also check and reset the tps while youre at it

 

I will try that. I noticed something else that may help narrow down the culprit. When running in lower gears( 1st and 2nd) and running at an rpm higher then 2,000 if you hold the gas peddle steady you can notice an increase and decrease in throttle, its very slight and if you werent looking for it you wouldnt notice it. any idea what may be causing that. I am going to try and reset the tps and check the IAC, I already had a chiltons but i thinking im going to get a haynes too

 

check tps with multi meter follow hayne or chiltons specs on how many volts it should have at idle postion and wot i believe it like .05 and 1.2 at WOT

 

before i replace anything this weekend, i just want to reconfirm with you guys....im going to replace the IAC and if that doesnt work im going to overhaul the TBI itself as it hasnt been done in 130k, i had it inspected and indeed the spray pattern on the injectors is off and the left one leaks a little or thats what i was told by my dad the one who installed the motor. I have HEAVY!!! smell of excessive richness burnoff from the exhaust, wether at idle or going down the road. I smell like a weedeater 24/7. just want to make sure its not something else causing the issue before i go into overhauling the TBI or replacing sensors.

 

That wouldn't be because of the IAC, since the engine isn't idling while it's doing that.
I would start with rebuilding the TBI first before investing in a new IAC.

 

SOLVED! You wont believe this I can't either.....it was the vacuum line going from the TBI to the PCV....it had a dry rot crack in it so it was leaking air the whole time. It solved the running rich and idle issues. Runs like a raped ape now! Still going to overhaul the TBI as the spray pattern is a little off and i think it is leaking out of the left injector